Okay, this isn't a new topic. But per Turbine Doc's request, I'm reposting my question about the Optic Bump....

When you advance the injection timing (bump the optic sensor), does it increase the duration of the fuel delivery or simply change the moment of fuel delivery?

This is a mod that is described as no cost. I'm assuming that means aside from the upper intake gasket....is silicone suitable in place of a proper gasket?

Only in a pinch.

As much as I've scanned my truck, I'd say the bump does exactly as tex describes in the original posting about this. It recalibrates fuel delivery toward the advanced side of the camring.
My top output increased from 61.5mm3 to 64.5mm3 but I get 64mm3 at 75% throttle instead of 61mm3 at 99% throttle.

Basicly what it does is advance your Start Of Injection (advanced timing) and keep the same End of Injection. Overall duration is increased, in the neighborhood of 4% @ Full Load. The earlier SOI helps, gets the fire burning in the combustion chamber a little earlier.

longer duration....more power....more fire....how much do the egt's go up when you bump the sensor?

Go down, you mean.

QMs right, it can actually lower EGTs.
Its completely recoverable, and safe I assure you.

How does the optic bump compare to advancing the injection pump? I am assuming that advancing the pump changes the timing throughout the range of RPM and throttle position/fuel demand.

Okay, this isn't a new topic. But per Turbine Doc's request, I'm reposting my question about the Optic Bump....
Thanks for this; there is a method to my madness.

QMs right, it can actually lower EGTs.
Its completely recoverable, and safe I assure you.
so we recomend this mod without boost and pyrometer gauges?

How does the optic bump compare to advancing the injection pump? I am assuming that advancing the pump changes the timing throughout the range of RPM and throttle position/fuel demand.
If we were talking about a purely mechanical system, 93-previous, then yes, advancing the pump's static timing will advance timing across the board.
DS pumps however are electronically controlled advance, PCM moves advance measured against the crank sensor. So changing static timing will only change your TDC Offset.
Optic bump will advance SOI timing across the board and increase fuel delivery at the same time.

I say try it, take note where the sensor is when you start, and you can even scribe marks on the optic with a screw driver to keep track of different settings until your satisfied.

so we recomend this mod without boost and pyrometer gauges?
Personally no IMO as per my recommendation in FAQ for more power http://dieselplace.com/forum/showthread.php?t=1078, NOTHING should be done that either alters fuel or boost delivery should be made without assist of gages, but TDG is confident in this, and PCM is still in the picture with full factory protection levels still (no chip or reflash yet right???), so it's probably as safe as TDG says it is.

Gages should be high on your priority list though, of must have equipment; EGT and boost at minimum, as many as you can afford after that, but hey thats my opinion.

How does the optic bump compare to advancing the injection pump? I am assuming that advancing the pump changes the timing throughout the range of RPM and throttle position/fuel demand.
IIRC been a while since I looked it over myself in FAQs TDG covered this in the IP how does it work thread. http://dieselplace.com/forum/showthread.php?t=10790

I agree with TD too, although I am confident this is a completely safe mod, gauges are essential not only for performance monitoring and tuning, but for diagnostic purposes as well.

Thanks for this; there is a method to my madness.You're admitting to madness?????:eek: :cool2:

You care to share ????

Oh no! Don't provoke him! He is gonna be sittin' in the corner drooling and giggling maniacally!!! http://www.dieselplace.com/forum/images/smilies/biggrin.gif

You're admitting to madness?????:eek: :cool2:

You care to share ????
This is what I sent to NVMNTLION wehen he asked similar question in PM earlier

So long as I can get my Meds, I can control myself from my fits of laughter outbursts http://www.dieselplace.com/forum/images/smilies/biggrin.gif , I run into my buddy Renfield & Dr. Jekyl (he-he/he-he) ever now and again. OOps time for some meds.<!-- / message --><!-- sig -->

Did my optic bump today. Piece of cake and I must admit...I am impressed, throttle responce is better, seemed to inhance power all across the RPM's excpecially my low end take off. Puffs black smoke at take off now but doesnt bother me.

You guys might also be interested to know I recorded my timing on my MT2500 scanner and before my timing was 14.5 degrees @ 55 mph and after I had 15.1 @55mph. Is this where I should be? I only bumped it once about 1mm or so and fired it up and it idled smoothly so I left it. Also, I dont understand how significant or "real World" this is but my Engine torque (according on the scanner) peaked at around 318ft/lb and after the bump I recorded a 336ft/lb at about the same RPM's.
Does anyone have more knowledge about the snap-on scanners ability to read engine output torque? How accurate is it? Is it actually my engines torque output at the flywheel or? If it is, how,what,when, does the ECM or whatever calculate it?

The ECM calculates inertial forces each time a cylinder fires to determine the next fuel pulse. I guess the mt-2500 can interprit this.

MT 2500 & T2 dispalys PCM calculated Tq & Hp, not a real number of actual rear wheel numbers, rpm-ambient conditions-boost-fuel delivery request and other data go into the calc, do things that PCM doesnt monitor(IC/Hi-pop/PMD resistor/opened exhaust & intake etc.) for more power and PCM is blind to those augments.

the black smoke is then unburned fuel. So if you increase your boost after the bump, you should see even more power gains? Does anybody have Kennedy's boost controler combined with the optic bump? If so......what's it like:D ?

Methodical Madness -

If an interesting\essential thread maintains direction in it's original topic, it is easy to 'search', and can become a FAQ.

If a thread branches out into several - interesting, or not - topical directions, it becomes difficult to define as a FAQ, and may simply be lost.

So, if you get a request to break off and start a new topic\thread, it becomes simple for newbies - or oldbies - to locate a subject by 'search'.

And, you may go down in forum history with your very own FAQ reference topic.:cool:

Me, I post for the humor - the proffered tidbits of factual data are, simply, filler............;)

Did my optic bump today. Piece of cake and I must admit...I am impressed, throttle responce is better, seemed to inhance power all across the RPM's excpecially my low end take off...

I dont understand how significant or "real World" this is but my Engine torque (according on the scanner) peaked at around 318ft/lb and after the bump I recorded a 336ft/lb at about the same RPM's.
Another satisfied customer ;)
I'm not sure as to the real world value of those outputs either, but I'm impressed you actually, although not scientifically, noted an increase in TQ output.

So far I like it. I should've done it sooner. I would have never known about it if I had'nt found this sight and been searching past threads. Then Ya'll started talkin about it again and I could'nt stand it any longer...had to do it. Glad I did.

I wish I understood the parimeters of the scanner info a little more. The more time I spend with the scanner the more I seem to learn.
I know those torque number increases I was seeing at peak arent actual expecially since I was watching the scanner and the road at same time, but what I did notice right away on the scanner is that at idle before the bump I had 9 ft/lb and after the optic bump it read just 4 ft/lb at idle. At first I was pissed when I saw that, but after my test drive I figured I gained it back at a different RPM because I undoubtedly felt an improvement.

Plus I cheated and practiced first on a core pump I have off a 95 TD. I didnt want to tell Ya'll that because I felt dumb after seeing how easy it was to do.):h

BornReady6.5
I think you just advanced the learning curve. :D

You know what they say....Theres no such thing as a dumb question.......I just seem to keep answering my own all the time! ):h

Did you happen to notice a difference in Fuel Quantity @ Low Idle? Stock should be 9~10, and 'bumped' it should be slightly lower.

the black smoke is then unburned fuel. So if you increase your boost after the bump, you should see even more power gains? Does anybody have Kennedy's boost controler combined with the optic bump? If so......what's it like:D ?boost controller, boost fooler, 3bar map, the result is the same, more air and fuel make the engine run.

You can extrapolate how far you're bumped by fuel output at idle. I'm at 5mm engine warm.

No, I didnt pay attention. After the bump my fuel rate is 6.7 to 7.0 @ cold idle. After the cold/high idle went down it seemed to steady at 6.4 (mm3).

QM just explained why I asked, at warm idle it gives an accurate display of just how far you've 'bumped' the optic, and how much more you could get away with.
You can go until it reads in the 4-5mm area, but if you go further than that, it will act funny and you will be able to hear the engine searching to maintain L.I. speed.

Dang! So you think I'm a little high. I figured I would be because my truck was cold. Let me go get a sodypop and get another reading while its warm. I dont think I bumped her to far cuz she runs great, but heck,I dunno. I let you know in a few min. Thanks texas

Ya, I'm about 6.3mm3 after the engines been warmed up at idle. Now that I am clear on where I need to be, excpecially with the help of the scanner, I think I will turn her back a hair and get her around 5 mm3. Thanks for straightening me out guys. I really appreciate it.

No no, the further you bump the sensor the LOWER the LI fuel reading will be. Moving the optic too far, will give you too low a delivery quantity at idle...

Let me try and explain what it is were looking at here OK ;)
Regaurdless of whatever the scanner says, your engine takes a specific fixed fuel delivery rate to maintain L.I. speed @ a specific speed/ engine temp/ load (A/C etc.). Agreed?

Now, when you change the optic sensor setting, this L.I. reading will vary according to the scan tool, BECAUSE the PCM is programmed to coordinate a specific pulse width to a specific delivery rate from the pump BASED ON STOCK CALIBRATION of the pump. When you change the position of the optic sensor, you change the calibration, in this case, your making it so the pump delivers MORE FUEL than it was originally calibrated to.

The PCM has now way of knowing what you did, but now it shows to be delivering less fuel but the pump is really putting out the exact same quantity as before, based on our previously established fixed fuel rate for fixed speed/conditions. We can take advantage of this to determine approx how far the sensor has been moved.

Clear as mud now? ;)

Ok I'm a little confused. I thought around 5mm3 was optimum and I am above that. You dont think I should move it a hair back to the drivers side and use the scanner to get her on 5mm3?
Also, as long as we are kinda talking about timing, let me know if my settings are where they should be.
TDC offset is -3.7
Actual timing is 15.6 @ idle.

I was searching past forums to see if I could get a idea where TDC offset should be and I couldnt find anything. The reason is because while on my test drive a few min. ago I noticed my TDC offset was -3.7. Does the bump change that or no? If I remember right, thats what is was before I did the bump. Is that where its supposed to be? Shouldnt my 97 ECM do it automatically or should I reset it? Hopefully I'm not annoying you to much...I know these topics are probably worn out. Thanks.

If you move the sensor 'back' in the direction where it was then you will get a higher L.I. fuel quantity reading like you had before, you have a little room to go further (towards pass side) if you like.

Yes it does change TDC Offset, moving the optic to the pass side has the same effect as moving the pump to driverside, advancing your static timing. What your actually doing is changing the relative position of the optic sensor to the camring. You should move the pump to the pass side (retard) to achieve TDC Offset -1.5 ~ -1.9.

Don't get too caught up on DES timing readings, this will change constantly with engine demands, load, temp, APP pos, etc. All you really care about is that ACT timing follows DES timing closely. DES just means what the PCM calculates the pump timing should be, thus DESired timing. ACTual timing is where the pump ACTually is, you just want it to be doing what its told.

O.K. texas I think I am finally seeing the light. With your help and also finding Doc's thread about timing and I am beginning to understand.
I will leave the optic alone and turn the IP towards the passenger side to try to achieve -1.5 to -1.9. right?

Right, get it in that range and you should notice more improvement still ;)

Sorry texas....the ole lady was yellin at me and we were late for a b-day party.

I will turn the IP tomarrow and let ya know what happens. Thanks alot...I really do appreciate it.

About 2.5mm to the driverside should do it.

2.5mm is for an un-bumped, stock pump at oem factory setting, QM.

The result is +5deg, for +8.5deg total at idle, which usually results in -1.5deg TDCO.

PCM controls idle by comparing inertial variances between inj events - called Cylinder Balance.
PCM does not know the 'bump' has been done, but the 'bump' increases fuel across the entire rpm range, idle to 4000rpm

Engine tries to idle faster from 'bumped' fuel increase, so PCM reduces fuel to maintain correct idle speed - scanner indicates that reduced fuel correction.

Cylinder Balance is only at idle, so once off-idle, the fuel increase is effective - hopefully, the PCM is not smart enough to remember that you 'fooled' it.

MT2500 indicates ~5.5deg TDCO for actual -1.5deg TDCO, but DES\ACT timing usually indicates +8.5deg at 690rpm at 180deg ECT.

Um..Let me see. So far I got a IP bump to the passenger side and Qm says drivers side, and from what I think I translate from gmctd is that I'm in spec.

I havent bumped it yet, but I'm fixin to after work. Anyone wanna tell me EXCACTLY what to do now?

Um..Let me see. So far I got a IP bump to the passenger side and Qm says drivers side, and from what I think I translate from gmctd is that I'm in spec.

I havent bumped it yet, but I'm fixin to after work. Anyone wanna tell me EXCACTLY what to do now?
The optic bump is pass side and the pump is rotated driverside, use gmctd's number's for the mt-2500 and set act time to 8.5 *.

B4 you do anything, let the engine warmup above 180eg - then check idle rpm at ~690, DES\ACT for ???, and TDCO value for ???.

Any scanner readings taken below 180-190deg ECT will be unreliable, particularly below 70deg ambient, because idle rpm effects advance and fuel rate.

Then, post idle rpm, fuel rate, DES|ACT, and TDCO as seen on your MT-2500.

TDG can then tell you which way to jump the pump, for the bump............

Sounds good. Thanks guys. will do after work . Thanks for all the help.

Whats that? pump jump bump dump? LOL
The further advanced the pump is, the LOWER (more negative) the TDC Offset.
Since he is already at -3.7, he's too far advanced, and needs to retard the pump to the pass side. After you move the pump, just try, for our purposes here on the site, and warm the vehicle up, take it for a drive, restart it a couple times and see if it won't relearn a new Offset on its own.
Ignore DES/ACT timing readouts.

How many times or how long does it take for the computer to relearn the timing? And can I turn the pump slightly while its running? Or does it need to be off.?

Truck off. It's a pita but you'll get it in a few tries.
Do the ENgine HOT! key on APP to floor for 1 min. Key off 1 min restart manual TDC relearn.

Okey dokey...keep ya'll posted. Thanks.

Truck off. It's a pita but you'll get it in a few tries.
Do the ENgine HOT! key on APP to floor for 1 min. Key off 1 min restart manual TDC relearn.

TDG - re-read my post on MT-2500 TDCO vs actual TDCO, as read with TECH-II

I see what your referring to now...
The 'Time Set' Function correct? This is a tool to approximate TDC Offset. What this does is put the pump at full retard and compare it in real time to the crank sensor. Expected value is approx 3.5deg. 3 will give you a ~0 TDC Offset, 4 will give you ~-1. 3.5 is used because its middle of the GM spec -0.25 to -0.75.

Didnt get a chance to do my timing....had to work late and also have a terrible dust storm here...will try tomarrow.

O.K, Tried to do my timing last night and ended up giving up because I need to make a special wrench or something and I ran outa time.

Anyone got a idea on how to remove the 3 Ip nuts without disasembling half the flippin engine?

Also, just to recap, here are my timing specs after the optic bump. Can someone interpret them and see if I still need to adjust the IP?

DES Timing- 15.5
ACT Timing- 15.4
Fuel rate- 7.4 mm3
DES Idle- 638
Current DTC- 0
TDC Offset- -3.7
These #'s were taken at operating temp.
IF you guys think Im ok. then I wont mess with it. If you think I can benefit some more and enhance my optical bump...then I will do it.
I think I may be a little off because My engine seems a little loud and clacky. In fact, it hurts my ears when I fire her up cold.

I use a 15mm self-ratcheting. the actual IP tool is an offset 15mm.
you're a degree and a half too far on tdcoffset. You're looking for ~1.94-1.50*btdc.

I use a 15mm self-ratcheting. the actual IP tool is an offset 15mm.
you're a degree and a half too far on tdcoffset. You're looking for ~1.94-
1.50*btdc.
I think you are going to need the special tool the self-ratchet normally won't work on dual thermostat HO pump equipped trucks, I tried several different and finally broke down and bought the right tools, don't forget IP turn tool as well.

I think you are going to need the special tool the self-ratchet normally won't work on dual thermostat HO pump equipped trucks, I tried several different and finally broke down and bought the right tools, don't forget IP turn tool as well.
Ya, I already tried the gear wrench before QM suggested it, and I still couldnt reach them. I think I am just going to buy the tools. Any suggestions on where to get them? What are yours? You got a part #? Thanks.

Yea Part numbers would be nice?

I had more trouble with the '96 style than '94 no doubt, I moved the a/c compressor, lines attached. Haven't jumped into the newerstyle yet.

http://www.etoolcart.com/index.asp?PageAction=VIEWPROD&ProdID=6666

If anyone has a source that is cheaper...let me know cuz I'm ordering it tomarow.

+15deg DES\ACT at 630rpm is scary - we got +7.5deg on TD's MT-2500, where the TECH-II read +7.5deg, down around 600rpm.

MT-2500 read -5.5deg TDCO, where Tech-II read -1.95deg TDCO.

I do not think the OS bump could cause that +12deg increase over stock +3.5deg DES\ACT.

TD's low idle is caused by the hi-pop\hi-flow injectors - my truck idles at 690rpm with standard injectors

What would you suggest? Should I reset my offset? Are you saying the MT 2500 is not reliable?

Yes, reset it. you're too advanced.

Your timing figures are very strange, where the only change is 'the bump'.

I see +8.5deg at idle, and +12.5deg at ~2200rpm\60mph

I've been wanting to do some b4\after testing, but it is very difficult on my truck, compared to yours, where most procedures can be accomplished by standing in those holes in the Diesel front bumper.

Guess I'll just have to bite the bullet, here, shortly and :grd:

Funny thing is, my truck was wrecked slightly in the front, so I have a gasser front bumper on mine. I wish I had those holes to stand in. :lol:


Your timing figures are very strange, where the only change is 'the bump'.

I see +8.5deg at idle, and +12.5deg at ~2200rpm\60mph

I've been wanting to do some b4\after testing, but it is very difficult on my truck, compared to yours, where most procedures can be accomplished by standing in those holes in the Diesel front bumper.

Guess I'll just have to bite the bullet, here, shortly and :grd:

Yes, reset it. you're too advanced.
Don't change it yet not too far advanced, MT2500 displays different value than T2 , I'm in Boston I will be home this weekend & I can give you a good MT2500 number, I ran with -4.3 on MT2500 for 2 years before figuring it out, -4.3 MT2500 is about a -.75 on a T2 so you are in ball park for factory TDC offset. PM me and we can share phone numbers so you can call me.

Once again, you guys are mixing up two different things. PLEASE LISTEN TO WHAT I AM SAYING AND IT WILL MAKE THINGS A LOT CLEARER FOR EVERYONE!!!!!

A 4.3 degree reading on the TIME SET command means your pump is about .8 deg more advanced than the desired 3.5, which will give you about ~-.75 TDC Offset.

TDG let me handle this one direct via PM, I know EXACTLY of what I speak on this one, GMCTD, Billman & myself figured this out earlier last summer. MT2500 displays both time set and TDC offset, but the value on MT2500 IS different from what is displayed on a T2. trust me I'm not confused at all here, I described it in the OBDII time set in FAQs as well.

To be really C-L-E-A-R on this - MT-2500 displays TOP DEAD CENTER OFFSET TDCO as -5.5deg, when TECH-II displays TDCO as between -1.5deg to -1.95deg.on the same engine, a few short minutes later (long enough to switch scanners).

When TDCO is very plainly stated, it would seem to take a quantum leap to interpret that as TIME SET - IMO...........

Other than that seemingly insignificant detail, yes, you are correct in your stated TDCO resulting figure being based\compared on\to TIME SET figure, in degrees.

Which brings us, clearly, back to BR6.5's problem - we need to get a baseline, just as on CR's troubled truck last year.

I would suggest undoing 'the bump' to get an as-found reading with your MT-2500 - I am having some difficulty defining your observed\stated +15.5deg DES\ACT timing at idle, with engine at normal operating temperature of 180 to 195deg.

Your MT-2500 should read DES\ACT +3.5deg at idle, 690rpm, as oem stock setting - if not, determine why, before you do da bump.

If your TDC offset shows as -5.5 on ANY scanner then you will have a code for ODBI 34-stepper motor fault or OBDII P0251- Pump Rotor Cam Problem.

- I am having some difficulty defining your observed\stated +15.5deg DES\ACT timing at idle, with engine at normal operating temperature of 180 to 195deg.

Your MT-2500 should read DES\ACT +3.5deg at idle, 690rpm, as oem stock setting - if not, determine why, before you do da bump.

unplug the CTS and it will read 14-15 degs top CI advance.

Same thing when its cold outside, electronic cold advance.

It's thrown me off before when I didn't notice I'd knocked that connector off while messing with the timing.

If your TDC offset shows as -5.5 on ANY scanner then you will have a code for ODBI 34-stepper motor fault or OBDII P0251- Pump Rotor Cam Problem.WRONG TDG, have you ever used a MT2500 I have multiple times, and have contacted several others who have also and get same result, mine was verified with a T2 I know exactly what the delta is. Please desist in adding confusion. Anyone wanting to discuss it please PM me. MT2500 displays the value DIFFERENTLY than a T2, there is a correlation between the two, it's not wrong but only a different value display, -5.4 is same as -1.94 on T2 I suspect that -5.5 on a T2 which indeed will give the fault you are referencing would probably be displayed on MT2500 as something like a -10 or higher value.

Believe you me a LOT of study and experimentation was done by myself, GMCTD in Houston & Billman in NY on an independent truck on this, as well as 2 more local MS MT2500s beside my own, and 1 more T2 from another local owner, while in Houston last fall I also went by Balley and used his tool to get better understanding of what was going on.

All MT2500s displayed same value as mine value is not real in PCM error diagnostics which is why there is no code set, it's just a number once you understand the correlation then and only then can a MT2500 be used for TDC offset. Time set however works as a called out in GM spec. degree of timing is correct and matches what a T2 displays. Only diplay error is TDC as displayed on the MT2500.

Now, who would be fool enough to unplug the CTS when setting timing, quoth he.
Or, any other sensor, for that matter?

On second thought, don't answer that - we don't want to start any arguments - again.

Then, again, I keep insisting on ECT of 180 to 195deg when checking timing, and who, with a scanner, would ignore that, also?

Don't answer that, either - let's keep this civil.

Ok - steady....steady....wait for the valium to kick in....and, 10...9....8....7...6...5...4...3...and........

(Billman - I'll need to depend on you to keep count of the repeats, here, if you don't mind. I'm on valium, and them numbers keep bumpin' in to each other.);)

Ok - BR6.5,warm the engine up to operating temps, check your coolant temps with the scanner to be 180 to 195deg F, then get the DES\ACT timing numbers.

If the scanner sez -40deg temp, then your ECT thermister circuit is open, or the connector is corroded, broke, or unplugged.

BTW - the inst panel temp gage sender - driver-side head, front - is totally isolated circuit from the PCM ECT sender in the t-stat crossover manifold.

GMCTD,
BR6.5 & I exchanged #s we talker earlier today, trying some different things, I've been helping Nigel on the Page with the same issue.

Ok - don't push me, tim! Remember - valium is just a patch, not a cure................;)

First off, I want to thanks Turbine Doc for letting me bug him on the phone and helping me understand a little more about OB's and timing. I really do appreciate it. Actually, I want to thank everyone who has had a hand in this thread.

First thing I did was turn the OB back to where I had it, maybe a sliver of a hair still"bumped". Then, I marked my IP and turned it about 1mm towards the drivers side. Then, I warmed her up to 190deg. and then checked the time set. It was 3.4deg. Then, I reset the TDC offset, as per TD instructions in faq's. Startup was wierd and RPM's were high for a second then she settled right down. Smoothest shes idled since I've owned her. Checked my TDC offset and it was at: -4.2. A little shy of my -5.4 goal. Then I went on the test drive. BAM! WOW! Almost broke the tires loose on pavement. My trucks never run like that! Big difference.

Its amazing that I've been driving the truck for so long with the timing so far off.

Now, why is my act timing right on the money @ 3.4 and my TDC offset not? If I move the IP another mm towards the driver side, and reset the TDC Offset again, will that help? Should I leave it alone? I think I still have some room for some more advance...let me know. I will list my before and after reading below to see what I should do.

Didnt get ACT timing before but after it is 3.4 deg.
TDC offset was -3.7 now its -4.2
Fuel rate before was 8.0mm3 now its 3.2mm3 @idle
All reading where taken at 190deg coolant temps.

TDC & timing are related but are 2 different things, you can be in time but out of TDC, your-4.2 with snap on reading though indicates you are in factory offset timing range. Fuel rate looks low IMO, what idle rpm you showing I'm running 9mm at idle. In my truck the TDC offset won't occur until offset learn is initiated 1st, either with T2 command or ko/ko APP to floor, it will lay dormant for self learn until water temp gets above 170F.

It learns immediatley after command if water temp is above 170F. -5.4 is snap on setting for a T2 reading of -1.94, on cold mornings that maye be too much advance for some -1.5 is a milder setting giving good acceleration and power for towing, and more cold tolerant when cold advance kicks in, in winter months. I'm not sure what that equates to on a MT2500 I did not write it down when I was there last, now I'm at -1.94.

You could bump yours some more since your avg in time set is 3.4, I'd bump a little higher for 3.5-3.6 avg, then do offset learn and see what you wind up with, problem with MT2500 vs T2 it's a little more effort, plus as far as I know this works for OBD II trucks only that can do ko/ko AAP to flor learn initialte.

What is your timing reading of actual & desired timing warm engine not in time set mode.

...TDC Offset does not change running advance of the pump. All it does is set the pump within operating range so the advance can do its job.

Before my fuel was 8.0mm3 and after was 3.2mm3 @ hot idle, so I dont know whats up there. WOT readings seemed ok as I was 60-70mm and higher but was trying to watch the road.

Out of time set my readings where:
DES timing- 15.7 after 15.6
ACT timing 15.9 after 15.8
I'll advance it a notch more when I get my IP tool. I've gotta be close because my truck has never run so good.

63mm3 is near stoc calibration, 70mm3 would be an improvement.
Do you still have the optic "bumped" or not?

Very slightly. I put it in back in its original position almost to get a baseline for my timing....I may go back in once i get my timing squared away and bump it back.

63mm3 is near stoc calibration, 70mm3 would be an improvement.
Do you still have the optic "bumped" or not?

Before . WOT readings seemed ok as I was 60-70mm and higher but was trying to watch the road.


Use freeze frame feature on MT 2500 if you hit Yes button whils displaying engine data it will freeze the data until you hit yes again and start sampling it again that way you can catch info and still watch the road.

O.K. I got brave, printed off the instructions and the pictures, took a deep breadth and did the optic bump yesterday. The pictures and inscructions where great (thanks CR and TDG). Things went well and it was very easy, the truck started and I took it for a drive. Must say it gave the truck some snap !! The only other thing that I notice is that it does idle a smidge slower but smooth. Drove 100 miles today and the thing ran great.


I do not have a scanner http://www.dieselplace.com/forum/images/smilies/frown.gif but I am going to look for someone who does, I'm tighter than tight. I think that I am correct, I need to figure out fuel delivery at idle and the TDC number correct?? anything else ??

Thanks
Chris

Timing is ~3.5* stock but can be advanced to 8.5* (TDCO of 1.5*-1.94*BTDC). With the optic bumped you may find it more advanced than stock by a degree.

LOL, everybody gets so nervous when they do this the first time, but after they've done it once, I think everyone who's done it will agree that this is really a quite simple mod.

Those are the 2 important number too look for yes, Low Idle Fuel Rate at full operating temp should be 8~10 stock, 5~8 bumped. Lots of variables truck to truck so I can't put a specific number except you may have trouble if you go below ~4mm.

The other is TDC Offset, you need to relearn after the bump and it should be between -.25 and -2.1 to run properly, -1.5 to -1.9 for best performance.

TDG, do I remember correctly, The Bump is not suggested on re-flashed ECMs? I have Heath's and was thinking of doing the Bump!

Possibly, MDT has his bumped with a chip. So, it should work.

I did say that before, thank you for bringing that up, and after testing, on a test bench, I do believe it is safe.

Texas,

So I need to relearn the tdc??

That is get it warm, turn it off, turn the key to run, hold it WOT for a minute, turn it off, let it set for 1/2 hour correct ?

So after reading this post, it sounds like the optic bump will optimize the timing and fuel system to work together for greater output at the rear wheels. I do however have a few questions:
- since performing the optic bump increases the fuel rate, does this mean I would experience lower full economy? With diesel fuel at almost $2.50 a gallon, any loss of fuel at this point is not acceptable!
- do I absolutley have to have a scanner, or is it highly recommended?
- how does this effect emissions (I have to ask this since I live in AZ and am required to get emissions testing every year)?
- if I were to do this mod, does anyone have or know where I can get specific, step-by-step instructions on how to perfrom this procedure with a list of tools required?

Oh yeah....don't forget about cjk65's question above as well. Don't want to cause a distraction from the original issue.

jmkglloyd,

I did this and I do not have a scanner, I just want to find one and make sure that things where done correctly. When I do I am going to make sure I ask for the correct reading so if I need to fine tune I can. The guys on here need to now numbers before they can be of much assistance.

Search the forum for "Optic Bump" read the post titled " I did the bump yesterday" that is where I found the pictures. There is also a post from turbo junkie and TDG explained it step by step. The only special tools are the torx 25 and torx 40 and you want the torx 40 to be good, one that goes on the end of a rachet in order to break it loose.

I read and read and finally said what the heck, I was careful cause I have never done anything to an IP. It made me nervous but it was a piece of cake in the end. The guys here will help if you run into a snag.

As far as emissions I have no Idea and the mpg thing, from what I read are uneffected.

Good Luck

One quick question, is a scanner a requirement to do the optic bump?

Nope.

Not a requirement no, you can certainly do it without one and not have any trouble. The only reason you would 'need' one, is if you get a TDC Offset code, and mind you this doesn't change it very much at all, even resetting TDC Offset is not absolutely a must.

The bump is getting popular, Tex.
:D 6.5L owners are lifting the lid on their DS-4's.

So I noticed...what can I say, its simple, its free, and unlocks some real world ponies ;)

Ok guys. Finally did my timing after all this time. Took for ever to get my IP tools and ended up breaking 2 of the 3. Finally said the heck with it and ended up taking my T crossover off and stuff. Man those IP nuts are a PITA.

Anyway, my current timing is as follows: Still at 600 RPM, DES 15.7, ACT 15.4, my new TDC offset is -5.7, my ACT time set is 3.3-3.4. Fuel rate at idle is 4.8mm3.

All figures were taken at engine operating temp.

Truck seems to run even better. Only got to drive about 1 mile but still seemed to pull strong if not stronger. I will find out today, I have to pick up about 5500#'s worth of truck in Phoenix today, with lots of mountains to go through. 300+ miles round trip. Cant wait to see how she does.
I very tired and didnt get a chance to read the past threads, but I think I'm closer to spec.
I pretty sure I am still running a slight "optic bump"

What do Ya'll think. Am I good to go? I calculate my IP is roughly 2-2.5mm farther advanced than where I originally started.

After OTC warrenties my tools...I will be selling them. They aint worth a crap, I dont care what anybody says. I patiently tried for over a hour to fenagle them in and it just doesnt work. The only thing I liked was the IP turning tool......its the only thing that worked.....and I MADE IT MYSELF!!!!!
Alright, thanks for all the help guys. gotta get some shut eye.

P.S. I threw a new OPS while I was in there and now my LP stays on for less time when I turn ingnition on. Before the LP rattled till GP went out. Now it just buzzes for a sec. Also, my oil pressure is reading a little lower now. Normal? Thoughts? Thanks.

-5.7 on the MT2500 is probably too much I don't know what that equals to in T2 equivalent offset, but mine at -5.4 MT2500 indicated is = to -1.94 on T2; -1.94 is most offset I've seen majority of folks run, I'd back it off some, on a cold morning you will think the engineis rattling apart.

With a 4.8mm LI fuel rate, your DEFINITELY a little hot with the bump now.
I'm sure I posted a couple times earlier that ~5mm is as low as you want to go, and your at the upper limit of what the bump can do for you.
I agree with TD, you need to retard the pump a little, bumping the optic will advance your timing and you should retard the pump to compensate, not advance it.

How does 15.5 *'s advance at 600 rpm sound? Can you drive and look at timing? I would look to see what timing does when you accelerate, make sure it progresses upward numerically and what timing does it run WOT? I only get to about 18* WOT if you're hitting 25*WOT that might be interesting.

You should retard the pump the full 2mm you advanced it and then see where you're at.

Drove to Phoenix today. Total trip was about 300 miles. Truck did awful. High egt's high engine temps.

I'm now wondering if I have a advance stepper problem. I took my scanner with me on trip and my buddy was watching it. At WOT timing sometimes goes from 15.5 to 15.8, thats all.

By the way all my temps were skyrocketing, I realize I need to retard the IP back. But My timing should still advance right? That would explain my poor performance. Time set is still 3.5.

Afew times I would notice 4.5 to 4.8mm3 fuel rate at idle, and then I would notice 8.0mm3. A blip of the throttle would set it back to 4.5.
I am very discouraged but think I am making headway. Can anyone enlighten me on my advance? Thanks.

4.5-4.8mm at idle might be a little too hot and you should probably set the optic back just the tiniest touch, enough to get it in the 5~6mm range.

As far as pump timing, are you getting any trouble codes??

What I dont understand is i know I set the optic back where it originally was. Now sometimes I have 8.0mm3 and sometimes I have 4.5mm3

I also dont understand why both times I turned the IP my first test drives afterwards were awesome. Then its like something changes and its gutless again.

Engine sounds ok and there are no codes except when after the first IP bump I did the TDC offset twice and got a 0216. I figured it was me changing the offset twice so I erased it and it hasnt come back.

Do I need to be in timeset mode and then drive it to see if the advance is working? Because I'm just looking at the timing readings in regular mode and dont see a change in timing.

Did i screw up my optic? Or do I stepper motor problems?

You can't possibly be exactly where the pump was originally with that fuel rate. Your close no doubt. If you can see the scribe mark on the cam ring, which, I doubt you can, its going to be overlapped by the body of the optic sensor the way it is right now. Stock position the edge of the sensor is just right at the edge of the line, no gap and no overlap.

Are you sure your doing the Time Set right? you know you have to punch into that mode and hit the button again, and you will should hear the engine get quiet while the test is running. '97s seem to be very particular about TDC Offset, and if you get the pump too far advanced they will run quite strangely. Your's should relearn TDC Offset on its own in just a matter of minutes of driving from my experience.

I think your WAY too far advanced, and you need to move the optic sensor back just a tiny tiny touch. Whats your DES/ACT timing at idle? Are you getting a CTIME reading? I've also noticed on 96-97 models that if they pick up a timing problem, they stop monitoring closure time and display 0.00ms and trip a Short CTIME code.

Yes I am doing the time set right. I can hear the engine rpm go down and my act timing displays the 3.5.

Maybe I havent given it enough time to learn the tdc on its own, but we're talking several miles and startups with no change to TDC. Only way to get TDC to change is hold pedal KOEO 1min and off 1 min. Definatly changing the TDC figures when I do that.

When Im NOT in Timeset the scanner reads DES 15.5 and ACT 15.8. And those numbers do not change no matter where I bump the IP, or optic or driving hot or cold.

I have not tried to drive in Time set. Do I need to drive in time set to see if my advance stepper advance motor is working?

I did move the optic back but your right, I left barely,barely enough room to see the half the line. So I know my optic is close to original position but surely not enough to make me have 4.0mm3 @ idle......but like I said, One second I show 4.0mm3 and the next second I show 8.0mm3. And yes, my engine is fully operating temp.

Unless anyone thinks I have bigger problems, my plan is to totally start all over with timing. Put my optic back, and I am going back to my original scribe mark on IP flange and move it 1mm towards driver side and reset TDC. If I still cant reach my goal, I'll do it another 1mm.Then if that still doesnt work I am going to passebger side with the same tactics. And if I still cant get my friggin optimum settings, I am going to get full coverage insurance and 5 gallons of gas.

No matter what I do i just cant get the optimal .25-.75 TDC offset(-4.8 on MT2500). Currently, I am at -5.7 TDC Offset which should be approx. 2.1-2.3 (w/T2). (i think thats what i want)

I am seriously suspecting other culprits such as, stepper motor, IP, ECM. But, with that said, I am realy relying on you guys. Ya'll know your stuff and I appreciate evryones help. I'm really not as dump as I sound, I am semi capable of certain things and timing obviously isnt one of them. But I have learned alot about it thanks to you TDG, Td, Gmctd and QM. Sorry I am rambling...havent had much sleep. 14 hour days.

QM, What do you mean by 8.5 deg. Is that in Time set? Or in the reguler engine data section of the MT 2500? Or is that T2 numbers?

8.5* is in time set on the mt 2500

I had mine totally out of wack before, It's not that hard to get it back you just have to think about where you should be and start moving the pump towards that area. As the pump comes towards the passenger side those TDC numbers should lower, then reset the TDCO and look again.

When you say you have 15.5* timing at 600 rpm, I'm thinking it should be 8.5* timing at ~600 rpm.

~8.5 sounds about right for a warm engine
I still trying to wrap my brain around 15.5 @ L.I. engine warm and 4.0mm fuel rate jumping to 8.5..........Start all over sounds like a good plan.
I think the problem is too many guys are doing similair things at the same time and its hard to keep it all seperate.

Did the bump this morning. got a little worried when the whole thing moved:o: . came back in, searched the posts and was relieved to find that I only moved the cam ring? anyway, the idle was immediately smoother, and higher (around 700-750). when I reved the engine in park, it took a while for the rpms to drop below 1100. after running a couple errands, the engine idles at 600, which is about where it was before. It's definitely smoother idling, and I notice that I need to back off the accellorator sooner. It feels like the engine is working lighter than it did before. between the k&n, 4" exhaust and the bump, this is a different truck. I used to feel like my right foot was pushing it up the hills, not the case now.

Also, the exhaust sound has changed after the bump. More interior noise:rolleyes: and more exterior noise...kinda like a peterbuilt:D .

Its a well proven mod, and it definitely improves the overall attitude, responsiveness, and driveability of the truck IMHO. I want to try and get more feedback from you guys who have done this and let me know how your mileage has changed!

8.5* is in time set on the mt 2500
Time set commanded even with MT2500 desired should go to 0*, actual should avg 3.5*, 8.5* is actual & desired at idle when not in time set command.

Again time set & TDC off set are 2 distinctly different settings, but adjustments of TDC can change once TDC learn has been activateld with either a T2 tool or key on key off APP to the floor in OBDII trucks.

Command TIME SET - engine rpm drops some, DES should read 0deg, ACT should read +3.5deg, fluctuating some, depending on physical IP advance.

Should definitely NOT read +15.5 deg, DES or ACT

Try that, and give us a report.

Okey Dokey. I have been all across the board with my timing now. I've advanced, I've retarded. My DES and ACT timing never change. Never.

When I am in TIME SET MODE, my DES reads 0.
When I am in TIME SET MODE, my ACT reads 3.5 give or take a degree.(after i do TDC offset learn)

When I am NOT in time set, I am still 15.5 and 15.5. WOT, or accelerating, or in park or blipping the throttle my DES stays 15.5 and Act MAYBE drops to 12.8-13.5 ish.

Currently (mainly due to total frustration and weary of moving the pump) I am about 1 degree retarted (literaly). My TDC OFFSET now resides at -1.7.

Performance boils down to..well, I used to own a 6.2 that would smoke this truck.

Good news though. 1st time took me about 1 hour to turn IP. Now I can do it in about 15 min. with a leatherman. I also have a new warrentied set of IP tools, because they didnt know what vise marks look like.

If i bump the optic will that help with the P0251 code i am getting?

I hope something works.

DTC 0251 could be caused by fuel opacity, as in something in, or added to, the fuel
Could also be connectivity - disconnect and reconnect the Optic Sensor connector.

Try for a TDCO of -4.4(?)deg , BR6.5 - that should be approx -0.5deg and +3.5deg DES\ACT factory spec.

I would ignore TIME SET, as indicated by a GM Training Instructor, as it mainly served a function in OBD-I, and is in the TECH-II to service OBD-I vehicles.

When OBD-II systems learn -0.5deg TDCO, DES\ACT timing will be within spec, based on correctly functioning Stepper motor.
(Do you have any Current\History DTC's?)

FIrst, shoot for -4.4 to -4.7deg (use value indicated by Turbine Doc) TDCO, which should be +3.5deg ACT - do not TIME SET.

Then, do the 1mm Optic Sensor bump, do the TDCO thing again, noting the new value - according to TDG, it should be -1.5deg

Again, as always, forget about TIME SET with OBD-II, with one exception - TIME SET can be used to verify Stepper Motor action.

If you do not see any Stepper movement when truck is idling, do TIME SET, and Stepper should move to full retard.

End TIME SET, and Stepper will resume normal advance.

Is that comment directed at me GMCTD?
If so where do i start on time set/

THANKS AGAIN

Just some pointers on DTC0251, flanman5 - the timing info is for BR6.5

I did the Optic Bump ,nervously nonetheless, What a breeze.

It help with the rough idle smooth now.
I attached another ground strap and the starter is fastest now, way faster.
Starts a little better i think, but, still the nasty P0251 Code.

I will take for a drive tomorrow , watching kids.
Later

Born Ready, whats your ECT, IAT, fuel temp and MAP readings on the scanner? Somethings definitely not right, sounds to me like a sensor problem.

Flanman, have you reset the 0251 code and it keeps returning? 4 things will trip an 0251 Code. Stepper motor/advance piston failure, Optic sensor failure, bubbles in the fuel supply, or your TDC Offset is off. A scanner will tell you which one it is.
If the stepper motor failed or the advance piston is binding, your ACT timing will be very slow to respond to DES.
If your optic sensor were on the fritz, or you had air in the system, you should be able to see Missed Cam Reference pulses appear.
If your TDC Offset is off, you will notice the DES timing will be lower than ACT, meaning you need to retard the pump, or when you drive the truck you will see DES timing go higher and ACT not get as high meaning you need to advance the pump. Also, your TDC offset will probably say 0.0 if this is the case.

I dont have a scanner, i just have a code reader.
The dealers would say it is the pump so no going there.

If i start it it does not idle but when i rev it up it idles great.

Didn't we establish that you have a faulty optic sensor? Sounds like your running in limp mode. Replacing the pump is the only cure for your woes I'm afraid.

Figures were taken @ idle.

ECT- (v) 1.89v
ECT- 199deg
IAT- 153 F
FUEL TEMP- 115F
BARO- 67
Boost- 67

Anything look outa wack to Anyone? I Still Show 15.5 ACT. My ECT temp also matches my gauge, give or take a degree. Outside temp was about 90F.

WHOA! Intake Air Temp is 153F!!!! I don't think so
BARO and MAP reading 67kpa? should be right at 100 (atmospheric pressure) at idle.
Replace the IAT sensor and see what you think. Also, check the Map and Baro sensors for 5v reference, you either have low voltage/weak ground/faulty sensors/ECM problems.

Funny, I just replaced it. My CES light came on while in mexico and when I reterned It was a IAT code. ONly one in town was one from standard. light went out. No codes ever since.

I only have the map sensor on the intake but will check for 5v. Also, will my 3 bar throw off that reading?

New figures while cold. Let truck sit for about 4 hours.
IAT- 102F
ECT- 4.something v.
ECT-98 F
Fuel Temp-110
I realize here in az the temp right now is about 70-75 degrees. But these Numbers still seem high. Also, Do ya'll think this would affect my timing? The 15.5 timing is really pissing me off. Reflash time? IP time? Truck starts and runs good until operating temps hit, then shes like a old 6.2. Read my previous thread a few back with my IAT figures....I think TDG has enlightened me about needing a new one. ANd yes, I now have more questions then answers.
Figures were taken @ idle.

ECT- (v) 1.89v
ECT- 199deg
IAT- 153 F
FUEL TEMP- 115F
BARO- 67
Boost- 67

Anything look outa wack to Anyone? I Still Show 15.5 ACT. My ECT temp also matches my gauge, give or take a degree. Outside temp was about 90F.

So what you are saying is i need a IP?

?

New figures while cold. Let truck sit for about 4 hours.
IAT- 102F
ECT- 4.something v.
ECT-98 F
Fuel Temp-110
I realize here in az the temp right now is about 70-75 degrees. But these Numbers still seem high. Also, Do ya'll think this would affect my timing? The 15.5 timing is really pissing me off. Reflash time? IP time? Truck starts and runs good until operating temps hit, then shes like a old 6.2. Read my previous thread a few back with my IAT figures....I think TDG has enlightened me about needing a new one. ANd yes, I now have more questions then answers.

That doesn't seem too hot, the IAT sits on the upper intake and gets all the heatsoak after shutdown.

Flanman, you need a pump, yes.

BornReady, you say you just replaced the AIT sensor or the MAP? the reading you should get at idle for AIT, should be almost exactly ambient temps maybe a couple degrees higher from crankcase vapors, but not 30 degrees more. The turbo doesn't create heat until the turbo is spooling, compressing the air, at idle you don't have that.

I see your sig says 3 bar map, well it looks to me like you got a faulty one, 100 give or take depending on altitude and weather is normal. 67 is way too low, do you still have your old one to try?

Can t i just replace the optic sensor?

theoretically yes, didn't you say you ahve an old 5288 pump? I know that rebuilt pumps aren't cheap, but your getting a complete rebuild, all the updates and a warranty, its worth it.

No i have the 5459 pump i that is was a updated pump?

Even if all or even one of these sensors is bad.....would that explain the 15.5 deg timing?

Flanman, you need a pump, yes.

BornReady, you say you just replaced the AIT sensor or the MAP? the reading you should get at idle for AIT, should be almost exactly ambient temps maybe a couple degrees higher from crankcase vapors, but not 30 degrees more. The turbo doesn't create heat until the turbo is spooling, compressing the air, at idle you don't have that.

I see your sig says 3 bar map, well it looks to me like you got a faulty one, 100 give or take depending on altitude and weather is normal. 67 is way too low, do you still have your old one to try?
If the truck was warm from driving it could easily pickup 30*'s at idle, I've noticed this before and after my IC install.

67 is low, there was a 3bar map graph posted recently, you should be to figure something from it as to what it should be. My resisted signal is in the low 90 Kpa. range

Flanman,
if your as confident in the condition of your pump as I am that you have a bad optic sensor, then by all means, get a brand new optic sensor and put it in.

BornReady,
I think, and I can't say for sure, that what your seeing is the equivalent of altitude compensation to your timing. Only 67kpa showing on the MAP makes the ECM think the air is so thin that you need advanced timing to compensate.
You said you let the truck idle for 4 hours before you posted those #'s right? That pretty much makes heat soak a non issue for IAT, check to make sure you have 5v reference and good ground, but I'm pretty sure the sensor is bad. This probably doesn't have much, if any to do with your timing problems, but it does mean your fuel is being cut back considerably.

i am pricing out a new pump TDG know where i can get one cheap?

cheap? not really, if yours is in 'good' shape, just have it rebuilt at cost of repair instead of exchange. Then you only pay for the parts you need and still get the warranty. Guaranteed it will be cheaper that way, if not, they'll just sell you an exhange anyway.

Any good shops in the Edmonton Region

Can you stand to be down with your truck for a while? And are you going to remove/replace the pump on your own or do you want a shop to do it?

I dont what is involved to take it out just the lines and the 3 bolts?

sortof... if you've not done it before, its a semi involved job, it can be done in under 3 hours though.
Basically, remove the intake manifold, undo the lines on the back of the pump and the inlet/return lines, and there's 3 bolts on the drive hub behind the oil filler tube you have to remove one at a time as you roll the engine over, and the 3 mounting nuts.

So i have to take off the timing cover?

nope, just the oil filler neck. Oh, and a bunch of wires to unplug, but don't worry, pretty much can't do them wrong, just don't forget any ;)

I really thank you for this info. I will call on monday for pump rebuilding.

Thanks again TDG

I'll be waiting to hear from ya. Actually, you'll probably be talking to Rudy or Mark and not me, but just let them know what you think the problem is and tell them you want yours rebuilt, not exchanged!

Where is that at?

Texas,

Per your request as a follow up on the "Bump" and MPG, as far as I can tell on my truck, it is not affected or if anything a slight increase...http://www.dieselplace.com/forum/images/smilies/rockon.gif One thing that I notice is that you barely have to press on the go pedal to hold your speed.

Needless to say I am a http://www.dieselplace.com/forum/images/smilies/biggrin.gif camper after doing this

I notice the same thing. Truck seems to move it self along and accelerate almost effortlessly after the bump.

Did the bump last night. All I can say is :rockit: WOO-HOO!!!I can't beleive how much difference that made to the truck! I moved it about 2mm to try it and I think I might try another 1mm tonight. Wow. It is like a totally different truck. All I can say is THANK YOU! to all the guys who figured this out and posted it for all of us to enjoy.

Did the bump last night. All I can say is :rockit: WOO-HOO!!!I can't beleive how much difference that made to the truck! I moved it about 2mm to try it and I think I might try another 1mm tonight. Wow. It is like a totally different truck. All I can say is THANK YOU! to all the guys who figured this out and posted it for all of us to enjoy.
Where's the timing at? Advancing timing to 8.5* makes it accelerate easier as well.

firefighter, let us know if it starts easier as well!!!!!!!!!

I haven't checked the timing since the bump but before it was 3.91. I am planning on doing some more to it maybe on Saturday, including rotating the pump a bit. I'll post the before and after results. It does start a little better now too. Seems to take about 1.5 less revolutions and does not sputter when it does fire now. All in all, I can't believe how much difference that simple little "tweek" made.

*grin*
And they said it couldnt be done....

My as well spun faster i dont know if it was the bump or the new ground strap i put on.
The truck itself idle way smoother too.
It was a great free mod and i too thank this site for the helpfull info.

I messed around with the bump again last night. My first effort was a couple of months ago, and didn't notice much of a difference in starting or performance.

Going by the mark I scribed when I first moved optic, I'd guess it was about a 2mm bump. Last night, I moved it back to 1mm, retightened the optic, and then centered the entire assembly (does that make sense to anyone?). I didn't notice any seat-of-the-pants changes, but this morning it seemed to start slightly easier and caugh less black smoke out the tailpipe and it was only 30F outside.

I'm not sure what to try next, but I'm willing to give it another shot if it's worth the trouble. Maybe my truck is already so "snappy" that the bump is unnoticeable? But I have no idea why that would be so, and I don't have another 6.5TD to drive and compare it to.

I put mine on the MT2500 last night. Before the bump my timing was 3.4 and after was 4.5. Then I got the bright idea to tweek it some more, well I went too far. It idled like a hot big block Chevy and seemed to make even more power untill about 75mph where it developed an intermitent miss under load. So, moved it back about half way to where I had bumped it the first time, idle is smooth again, but still a bit of a miss at 75 under load. Moved it back to a hair more than the original bump and everything seemed cool but then threw a code. LOL. I guess that's what I get for messing with a good thing;) , I will hook it back up to the MT2500 to see what it threw, I have a feeling it might have been an overboost code. I backed off the Turbo Master almost .5" and after the bump I am still making 16-17psi:eek: . Backed it off some more last night after that but didn't go for a drive to see where it is at now. I am shooting for a steady 14psi under load. Truck sure feels alot stronger now though than before the bump.

*grin*
And they said it couldnt be done....and they said it had been done before and discarded as a bad idea, LOL!

Its definitely not a cure-all, and if you have underlying pump/engine problems it may very well reveal them to you, but it is what it is, quick, easy and free.

Then maybe I'm revealing "underlying pump/engine problems" by not getting a very noticeable change in performance after trying the bump twice?

Hooked it up to the ol MT2500 again last night. Showed 1.6mm fuel rate :eek: at 600rpm and -5.7 for timing. So, needless to say, it got bumped back a bit and all hickups seem to be gone now. The code was an overboost so that got reset. Turbo Master seems a little sticky so I will take a closer look at it this weekend. Almost feels like a bur on the shaft or something.

YOu should notice your turbo will spool quicker after the bump, advanced timing, more fuel and quicker revving engine. Yeah, 1.6 is just a tad on the low side, and you could probably see and hear the engine hunting on decel I'll bet.
Your saying your TDC Offset was at -5.7?

..and you could probably see and hear the engine hunting on decel I'll bet.
by hunt, do you mean jumps down to idle on downhill slopes? If so, my truck definitely hunts more after the bump.

Yes, thats what I'm referring to, the PCM is trying to control the rate of decel, but since the pump is 'hot' and delivering more fuel than is expected, the engine will react differently than what the PCM wants. The resulting surge of engine speed causes the PCM to overreact and stop delivering and the cycle repeats.

Yup, that's exactly what it was doing. Another thing I noticed was at about 55-60mph on flat ground, I had such little pedal into it to maintain a steady speed and not accellerate that the converter would unlock. I am guessing that this would be due to the computer referencing pedal position/load/spead and thinking that you were really trying to decel. Lots of power though:D .Going to work on it some more tonight after work and try to get it right.

Your observations and interpretations are mine exactly.

Ok. After a week or two vacation from my working on my truck I think I've finally figured out my problem, or at least I am confident I have.

Before, I could never get below 15.5 deg. ACT timing no matter where I turned IP. I have been all across the range with the TDC offset and have seen everywhere from -3.2 to -6.0.

I figure the reason I am stuck on 15.5 is my crank position sensor has to be bad.....How did you figure that out you say? Well, I finally got a code. Yesterday while driving home my truck kinda felt funny and sounded different just for a split second...and Lo and behold...a check engine light. . First code I have ever recieved. And, guess what, a 1216. TDC offset error.
After some research I have narrowed it down to the crank sensor.

It definatly makes sence....so I ordered one today from the dealer. Keep ya'll posted to see if I can get some normal timing numbers now and feel the benifit from this Otic Bump thing.

Has anyone changed one of these? How tuff are they? Does the harmonic need to come off?

HB isn't in the way. CPS should throw it's own code and the engine should run limp if it's not working. Check connectors first. I've had oxidation on the pins cause intermittent connections, a little cleaner and it's woked fine since.

Yup, that's exactly what it was doing. Another thing I noticed was at about 55-60mph on flat ground, I had such little pedal into it to maintain a steady speed and not accellerate that the converter would unlock. I am guessing that this would be due to the computer referencing pedal position/load/spead and thinking that you were really trying to decel. Lots of power though:D .Going to work on it some more tonight after work and try to get it right.
I've noticed this but let me explaine further.
Empty is when it does this, especially cresting hills when you let the pedal out a little more. With a load the TCC stays locked and the pedal stays further in to keep the momentum up.

I installed a TCC reg valve with a towing spring and the difference is night and day.
TCC now locks without being felt and only unlocks when you're throttling so hard it downshifts anyways.

OK, stupid question time, where and what is the optic sensor?

I think in FAQs there is a link on how an IP works that may have photos of optic sensor, and also optic sensor bump thread is there