I just thought I would start a new thread to in case anyone wanted to know a little more about what really makes these pump tick, and eliminate a lot of the misnomers and myths associated with this system. So first, lets start off with the basic.


DS4 831-5XXX


(D)istrubuter Style, (S)olenoid Operated, (4) Plunger, (8) cylinder (31)mm plunger pump


Basicly its a rotary pump with a fuel solenoid in the rear of the pump that when energized, pushes the poppet valve closed to start injection, and opens to end the injection.


Optic Sensor: is locked to the cam ring and advances/retards with it. reads 2 tracks inside the pump that rotate with the drive shaft.


Lo Res track sends a cam pulse to the computer, that sends voltage to the PMD to close the Fuel Solenoid. It is also used by the PCM to measure timing relative the the Crank Pusle so the stepper motor can be adjusted to provide the desired advance.


Hi Res track is nothing but a counter. The computer takes several inputs (throttle postition, engine speed/temp etc. and resistor value) and converts that to a number of hi res counts for the fuel solenoid to stay energized to give the desired fuel delivery (Pulse Width).


[] Lo Res / Cam Pulse.... []


|||||||||||||||||||||||||||||||||||||||||||||||||| ||||||||||||||||| Hi Res Track


(1 )(2 )(3 )


( Pulse Width )


_________/lobe begins....peaks....and ends\____________________/


Hard to draw a cam profile with ASCII, but just imagine a cam lobe over the words there.


1) Cam Pulse sent to PCM, which signals the PMD and energizes the Fuel Solenoid, which starts to close. Duration here is approximated and will vary with engine speed (longer distance at higher speeds) and Closure Time (amount of lag between this signal and the fuel solenoid actually pulling closed). The computer also starts counting hi res pulses here until it reaches the desired count to end injection (Pulse Width).


2) Fuel solenoid is closed, but injection has not begun, Rollers still ride on flat between the cam ring lobes. Duration again is approximated. This gap is needed to ensure that variations in CT do not cause uneven start of injection events.


3) Start of Pumping: Rollers begin traveling up cam ramp, plungers are forced together and fuel is sent to one injection port. now this Duration is determined by basicly 3 things, calculated by the computer: throttle pos+other PCM inputs (temps etc)+resistor value. Now, Resistor value works like this. The PCM reads its value on startup and treats the 1-9 resistors as if they were -4..0..+4. That tells the computer that it needs to add or subtract X hi res pulses for the pump to deliver the appropriate amount of fuel which is what the pump is calibrated to.


thats the basics, now for the theory.


if you move the optic sensor slightly towards the oncoming ramp of the cam ring and lower the resistor value, you will get the same (1) it does not affect closure time, a shorter (2) and the pumping range (3) will only be slightly longer, and the total PW will be shorter. but now the pumping event will start slightly earlier (advancing timing ever so slightly) and providing more effective pumping time from the same pulse width, which is why the dropped resistor is needed, to compensate partially for the added fuel delivery by shortening the duration. Assuming the optic sensor is moved far enough to gain more fuel

TDG,
Welcome!
I'm really greatful that you've arrived at the diesel place.
Your advice and experience is sought after here.


I received the code for pulse bandwidth too short duration before I made the Optic change.
I have a #7 resistor plus 42" fsd extension and connections, maybe a 9 total resistance.
also my APP gives a volt spike on #1 and #2 resistors.
Also I have a 25 ohm switch on the MAP signal. I run it at about 1.12 volts, down from 1.45 volts.
Where do I need correction to give a long enough duration.
I saw this code after the change too.
Edited by: quantum mechanic

Interesting, I'm assuming your working on the 96 model truck then, surely only the OBDII computer would be able to assess such a condition. I'm going to have to say it has something to do with the 42" of extension, which is effectively 7' since the signal has to travel to and from the PMD. My electronics experience is not good enough to really estimate the effects of that much resistance, but I know that Solenoid operation and CT are both measured based on changes in voltage when the solenoid is opened and closed and this could possible throw the readings out a bit...do you know if your CT changed when you relocated the PMD?? I'll have to do a bit of research on that one, but thats my guess. Edited by: Texas Diesel Guy

It's the '94.
and yes the fuel delivery and idle seemed to change when I put in the extension.

well I think we need go no further then right? got to change your FSD cooler arrangement, or live with the code.....

It only flashes this code when under full load and above 2700 rpm.
other than that, I might rewire the extension with 20 awg intead of the 18awg I used.

20 is a lighter gauge wire, and would probably only worsen the problem, maybe go with 16 or 14 instead.

Excellent stuff, here, TDG - it is appreciated.


Do you know how TDC Offset is related to the wide slot for #1 tdc in the encoder wheel?


I see how it can relate, but what is the official stance on it?Edited by: gmctd

To be honest with you, I really dont know why they made #1 a wider slot, obviously so the computer can tell it from the other 7, but why it would care, I dont know. I never really thought about it to tell you the truth but sure the computer could just look for that longer pulse to set TDC Offset, or it could use all 8. Its also very possible that it might be there and completely ignored by GMs, stanadyne made DS pumps not exclusively for GM mind you, they designed the pumps and GM was their first customer for it. John Deere was planning to buy clockwise DS pumps, but for some strange reason they backed out...hmmm...I cant imagine why?? Just a thought, I really dont have a good answer for you TD.

According to what I've read, Stanadyne wanted GM to do further field testing, but GM insisted on '94 DS-4 product release.


Money rules....


Logically, the wide #1 slot is for the 5deg (+2.5, -2.5) max TDC Offset spec - allows electronic measurement and adjustment, similar to what you do with the mechanical optical sensor adjustment.


OBD-II PCM's are limited to +2, -2 to set the DTC.

TDG,


Here is one for you I have been trying to digest for years, when I got my truck used 1st thing I had to do was replace IP. I got a new IP at 37K under the warranty, I later bought a scanner & read TDC offset and value was 4.8 I ran that way for a year as I knew my dealer wouldn't do anything wrong factory trained & all.


Chewed over the procedure in the manual and info from TDP, decided to give TDC offset set a try myself, now I'm at -1.5 where I want to be, had to rotate to pass side & key on key off routine with APP to floor to initiate the learn.


How could it have run that far out of range, & not throw a code, is 4.8 a default offset the PCM runs with if learn has never been done, in the time set function desired timing forced to 0 the actual avg time was/is 3.5 deg. per manual spec.


You got any thoughts on this I've been dying to ask somebody that knows IP & PCM control logic interaction intimately

QM


What code are you seeing I've never heard of a code from FSD/PMD they usually just quit & no indication of why; which is why it's so frustrating to someone that doesn't know about their shortcomings.


TDG has more or less stated the FSD is a current control device, if this is the cause of your fault, smaller gauge or longer length of small wire will add resistance which will raise current draw of circuit, larger gauge wire would reduce the draw, what I don't know & maybe TDG can elaborate does higher current on FSD add or reduce fuel.


TDG, from an earlier thread if I read correctly a smaller resistor in the FSD added fuel, this contradicts what I've seen elsewhere the larger the resistor= more fuel, is this correct?


QM,


On the code front I was throwing a boost code at hi power when i 1st went to the Heath 2.0 reflash, found it was a bad MAP sensor Giving Hi out of range input to the PCM hidden by the MAP "boost fooler" I replaced the MAP and fixed it, I wounder if Map is tweaked too low with your fooler it is setting a code as a result.


If I remember some previous posts you recently added more offset(resistance) to the MAP signal, did you have these codes before you did that or has it always been there with your remote/long harness FSD cooler set up. One thing about this PCM code setting you really have to be on you game I've seen many sympathetic codes set totally unrelated set, it's as if 1st seen anomaly sets the code masking what is really happening.


In the game of modification I find myself asking what did I do last, oh that sucked; I better not do that, and you need a scan tool or gauges up the ying yang to see what is going on as a result of the change.Edited by: Turbine Doc

First off the lower resistor value I mentioned and may not have clarified properly was to lower fuel delivery to offset the increase from moving the optic sensor.


Also changing voltage/resistance will affect closure time but, as per my diagram, the solenoid closes before fuel is delivered so changes in closure time do not affect fuel delivery.


The #1 slot is not 5 degrees in length, it is only slightly larger than the other 7 and could only be used for the computer to discriminate it from the others. TDC offset is determined by bringing the pump to 0 advance and comparing Cam Pulses to Crank Pulses and calcualting the time between in degrees difference in the two.


As long as the computer can set a desired advance and the pump can comply it will not set a code and the truck will function proplerly. The IP has a greater advance range than the truck will ever ask for, thus the varied TDC offsets you can get away with. So if you were running a 4.8 offset, then when as long as the computer never asks for an advance of less than 4.8 (which would be 0 to the pump) then the pump will be able to comply and no codes set.Edited by: Texas Diesel Guy

TDG, I think we are confusing base time set with TDC offset 2 different things, when I go time set using time set function of my Snap-On scanner, the PCM forces time desiresd to 0 actual time is 3.5 deg which is right on spec for timing. It's the 4.8 TDC offset I'm asking about, once out of base timing set with the scanner.

have a 1995 6.5TD with a code 36 (long Pulse) biggest problem when it triggers the SES Lite the Cruise Control drops off. I have checked all the grounds changed PMD Waste Gate Sol. Checked Lift pump (good) to no effect. Previous owner said all was fine--had a stumble at 58-64 MPH and disconnecting the EGR cleared that up. I was wondering if shifting the Optic Sensor will affect the "Long Pulse" ? If so looking down on it in which direction? and how much should I move it? The lite will go out if I decelerate or accelerate- Temperature does not seem to be a factor. Finally after a year of searching it appears that there are people out there that understand the I.P. wonderful-


Artie up in Ct.http://dieselplace.com/forum/smileys/Cry.gif

optic sensor and fuel solenoid are completely unrelated. The only thing that might get you by temporarily, and its a big might but if you've only recently gotten a code for Long CT, it might work, get some lubricity additive and load up the fuel with it. Not some junk wal-mart injector cleaner or water remover, lubricity additive like Stanadyne Performance Formula or Racor Additive. It might make enough difference to keep your fuel solenoid kicking a little longer and its a real good idea to run some anyway.

Thank you- I guess I misunderstood the "Theory" in the Topic. Is the Fuel Solenoid a replaceable item? (rob one from another?) realize now you are trying to communicate with a guy that started out with a 1928 Stude and worked his way up to a 36 Ford.) Will try the Additive soon as the Holiday is over. Love the truck but the complexity of engineering in the Electronics certainly was a big jump from my 82' 6.2.

Hi,

I wonder what the operating temperature range of the pump is and at what temperature fuel should be that goes into the pump.

Are there any problems with the pump when running SVO? To run SVO, I'll install a heat exchanger that takes heat from the cooling system to heat up the SVO and eventually the Diesel. Fuel temp will be about 70 degrees Celsius when it enters the pump then.

Does it make sense at all to heat up the Diesel? Once the heat exchanger is in place, the system could be set up to run either Diesel or SVO through it.

Maybe the SVO can be made even hotter by placing an electrical heater into the tubing after the heat exchanger. Would you recommend such a thing?

SVO? I dont know what you mean? But to answer your question normal operation temp of fuel is approx 130-140F while running, of course this will vary from truck to truck. Why in the world would you want it hotter though? the only reason you would ever heat it up if your somewhere cold enough that there is a danger of gelling or parrafin starting to solidify and plug the filter, but once you get it above freezing, thats it, I can't think of any other benifits of a fuel heater. Hotter fuel will have lower viscosity and the pump will not be able to function as efficiently, nor will it be able to cool is onboard electronics as well. Edited by: Texas Diesel Guy

TDG,

the idea is that by heating Diesel fuel, viscosity is lowered so that the fuel vaporizes better when injected.

SVO means 'straight vegetable oil' --- oil from rapeseed, in my case. SVO has much higher viscosity than Diesel, thus heating the SVO and lowering its viscosity is a very good idea to make it useable. In theory, the hotter you make it, the better it works.

Usually, the SVO is heated either electrically or by a heat exchanger. The heat exchanger takes heat from engine oil or from coolant water to warm up the SVO.

The heated SVO will be at about 160F when it enters the IP. At that temperature, its viscosity is still higher than that of Diesel.


A tank fill of Diesel costs about EUR 80--95 here. Running SVO would save me about EUR 20--30 per tank fill. One fill lasts a week only, so SVO would save me about EUR 100 per month.

The costs for the conversion to run on SVO are about EUR 300--400: heat exchanger, some tubing and a solenoid to switch between Diesel and SVO etc., lift pump, a tank to hold the SVO (from a wrecked truck or so).

Worthwhile, imho, but only as long as I do not brake anything, especially not the IP :)

I'm very interested in SVO. I've been collecting pieces for a homemade system.

SVO is high in glycerine, solidifies at realtivly high tempatures and oxidizes rapidly.

I've read that you have to switch between diesel and SVO, especially at shut down.

TDG, the SVO should lubricate well, but it might crud up the optical sensor..
any other parts of the pump you think will suffer?

QM,

it's true that you should switch. The engine is hard to start --- if at all --- on SVO once it has cooled down, so a few minutes before shutting it off, you switch back to Diesel. When you start it again, Diesel is in the system, and after a few minutes the engine is warm enough to run on SVO.

I've seen very nice plate heat exchangers being sold on Ebay for less than EUR 50 :) I won't recommend electrical heating, as it hasn't much heating power, but draws lots of currents from the alternator --- while more than enough heat is available for free from the cooling system.


I'm starting my holiday trip this evening; I'll be back at the end of the month. I think I'll go further into the issue after I'm back. I'm looking forward to hear what you've found out then :)

if the viscosity is much higher, I would be concerned what it would do to your CT. Sounds like it will make it longer and possibly outside tolerances setting a Code 36. The hydraulic head in all these rotary stanadyne pumps is very tight and precise designed specificly for the viscosity of diesel fuel, go much above that and you risk head and rotor damage/seizure. I can only guess, I dont know what the viscosity is for SVO at 160 compared to diesel and it may work fine, it might not, or it might work for a while, hard to say with out more info.

Hi to the Wizards ! I noticed what "appears" to be an "add on" has a male an female connector on a pigtail about two inches each in the center of which is a black module about 2-1/2" long 3/4" wide and 1/2" thick bearing the numbers 12553327 ! It was in series with the lead that goes to the pump. Past experience has dictated that NOT usual does a Manufacturer do this where an item in series has the same plugs. I removed it and went for a short drive the SES light did not trigger (yet) I have cleared the Code 36. Does any one have an idea as to what this unit is and does? I could NOT identify it as a GM number. Previous owner just continualy stated "the Turbo had been turned up" (so much for that)Thanks Artie


1995 6.5 TD Silverado 140,000

Did it go to the black box on the side of the pump and have 7 pin connectors? If so, it is supposed to be a fuel controller but they don't/can't really do anything.

I think he's talking about the filter wire going into the optic sensor, there's a GM Service Bulletin saying to take them off and plug the wire in directly. But it has nothing to do with your code 36.Edited by: Texas Diesel Guy

it is a "6" pin connector and has "25V in big numbers on one side. Thanks to all!! Artie


95 6.5TD

I meant 6 pin in my last post but now see that the optical sensor is also 6 pin. Does it look like this: If so, it is what goes to the optical sensor.


http://www.dieselplace.com/forum/uploads/DF7_plug.jpg

I think he's talking about the filter wire going into the optic sensor, there's a GM Service Bulletin saying to take them off and plug the wire in directly. But it has nothing to do with your code 36.


What problem does it fix to remove it? I like getting rid of un-needed stuff especially if it helps something.

yes that is the item- thank you-sad to hear it wont fix my 36!! Dam !! Does anyone knowthe intended purpose of this filter?


Artie

It's just an electrical filter designed to 'clean up' the signal from the optic sensor. I could only guess, maybe GMCTD or someone else on here could explain it better, but the high res signals especially are going to the PCM at high frequencies, and the signals need to electricly consistent so the PCM doesnt have any problems processing the inputs.Edited by: Texas Diesel Guy

The GM # 12553327 electrical noise harness was to filter alternator, lift pump, a\c compressor, blower motor, etc, synchronous noise which disrupted optical encoder output.


Symptoms - hard starting, rough running, stalling.


Which Bulletin recommended removal, and why?


Were also some problems with crimped connections, which resulted in all inj pump harness connections being crimped and soldered.


Almost fergot......


DTC 36 is Inj PW long, which could be solved by lubricity additive in fuel to prevent Fuel Solenoid dragging, as suggested by TDG.


Fuel Solenoid could be replaced - it's under the black boot at rear of inj pump - red and black wires from FSD\PMD.


If changing fuel source and adding lubricity doesn't cure, usually means inj pump replacement.


More so, if the engine bay harnesses have had some preventive maintenance routines for oxidation, corrosion, and etc. Grounds included - low volts to IP means slow response times.Edited by: gmctd

I'll double check with our dealer, they supposedly sent us the bulletin, although I did never lay eyes on it.... Replacing the FSOL means rebuilt, can't just unscrew it and screw another one in. Has to be set to allow the poppet valve inside a precise amount of opening. I have however read the bulletin from Stanadyne about IP wiring harness between PMD and FSOL causing CT problems, which is why they now sell new PMDs in a box with new heat distributing pad and harness.


But yeah, try some additive, not from wal-mart and not injector cleaner. In addition to Stanadyne and Racor, Powerservice and Rotella's additives are pretty good too.

You fellows are great !!! Thanks for the input. Another quick question will a pump "DS4831S5067" work okay on my 6.5 1500 Silverado 1995? Hate to say that it only triggered the SES (code36) once today after removing the Filter.


Thanks again Artie in Ct.

5067/5288/5459/5521 are interchangeable and supercede in numerical order, yes it will work but it is quite an inferior and problematic pump.

THANKS CERTAINLY PAYS TO ASK! --The help that I have received has been outstanding- wish I had found this Site a year ago! Has anyone dealt directly with Stanadyne? They are only about 50 miles north of me, would it pay to run up there?http://www.dieselplace.com/forum/smileys/Hug.gif


Artie

The "S5067" indicates rebuild by Stanadyne - Blue Stanadyne Label and Green Tag attached to pass-side front corner would indicate better than "-5067", but would be the acme pinnacle of wunnerfulness if rebuilt to -5288 specs, as noted by paper label affixed to rear of pump - latter part of '95 thru at least '97.


Otherwise, as noted, be best to get a later pump.


Try a couple or four tanks of Shell or Chevron from a high-volume truck stop, and add lubricity, first, though damage may have already been done.


Fuel has a tendency to "sour" - the longer it sits in the ground tanks the more problems it can cause, particularly if that was all that was ever used in the truck prior to current ownership.


Oops - I was compiling while you were posting.....


I'd call, first - see if they are 'approachable'.Edited by: gmctd

What is the procedure for moving the optical sensor? This sounds real iteresting, but I dont want to muff it all up.


Thanks!


Tim

Before I go through the process again, please read the earlier posts and then ask me specific questions, there's a lot involved in what your doing, but its a really simple mod.

I just read this post and I'm glad I did. This actually puts a lot of stuff in to perspective for me as I am working on copying then re-designing the PMD.


Thanks TDG! I will be pickin your brain in the future!

and I yours http://www.dieselplace.com/forum/smileys/Wink.gifEdited by: Texas Diesel Guy

Before I go through the process again, please read the earlier posts and then ask me specific questions, there's a lot involved in what your doing, but its a really simple mod.


Tex, when you say previous posts, do you mean in this thread or in another one? I read it all, and I under stand the whys, but I don't understand the 'hows' of moving a optical sensor.


I guess I need a 'Tab-A-into-Slot-B" kind of answer


thanks!


Tim

cowracer,
the thread started at:
www.dieselplace.com/forum/forum_post.asp?TID=10883&PN=3 (www.dieselplace.com/forum/forum_posts.asp?10883&PN=3)

Thanks Quantum!


The link you gave was bad, but it gave me enough info to search and find it!


The correct link is http://dieselplace.com/forum/forum_posts.asp?TID=10883&KW=optical


Tim

Hi,

I'm back from my trip to Sweden!

QM, have you found anything more about using SVO yet? What TDG writes doesn't sound all that good, and I would rather not risk damaging the IP. Maybe we should start a new thread on that topic.

BTW, QM, I tried to send you a PM, but you username seems to be too long to do that.

TDG,
Talk to me about the optical sensor and operation.
Is that an EM coil and pickup that senses the gear that runs off the steppergear?
I have rust on the working side of the pickup.

You lost me there Quantum... The optic sensor is under the top cover that reads the data disc inside that turns with the rotation of the driveshaft of the pump. The stepper motor is just an arm that moves up and down at the command of the PCM. Are you telling me you have rust on the stepper motor or on you optic sensor?

My bad. I mean where the optical eye is and the copper plates.
I guess corrosion on the copper plates shouldn't matter much.
I must've gotten some bad fuel because what was in the IP was so cloudy I couldn't see the sensor in it.
It was working ok, then on the way home I got code for cam sensor fault and the actual timing was reading 0.0
Where is the cam lobe sensor?

cam pulse is the lo res track on the optic sensor, cloudy usually means water, which would explain the rust. Optic sensor is particulary sensitive to water in the fuel, obviously it clouds the fuel making it harder for the optics to read the data disc, but after prolonged exposure it can cloud the lens too. The 'copper plate' is a brass bushing on the bottom of the transfer pump/drive shaft. Edited by: Texas Diesel Guy

I think my dad was right and that under priced Diesel was bad.
I had to put my timing back at 5.5 because it stopped reading it advanced.
I want to say that I noticed the difference in not having the "bump" on the optical.
It ran the hottest it has in a long time and power was way down.
I burned most of that tank out today and fueled up again but lost the cam lobe counter after.
I did see the data disk with all the marks on it.
Can you tell me what happens when you move the optical without loosening the T40 scerw?
I have had it everywitch way trying to make the truck run.
I started taking the cloudy diesel out with a turkey baster and replacing it with fuel out of my tractor.
It would work and I can only guess because it could read it at start up and with the cloudy fuel it couldn't find it's way.
Edited by: quantum mechanic

If you move it with the screw tightened then your just moving the cam ring and when the truck starts it will go right back. If you could watch it with the truck running you would notice the sensor, along with the cam, would move to the driver's side with more advanced timing, and pass at lesser advance. Again, the computer reads the difference between when it sees a cam pulse and the corresponding crank pulse to determine/adjust what advance the pump is at.

Two days ago I swear it jumped time or something similiar.
I was working on reestablishing the setting I'd had previously and liked better.
I got it bumped to far and it had the rough idle problem. Then I turned it off and restarted it with my scantool reading.
when it restarted it was idling at 880 and reading 14.0 deg actual and desired, the rough idle was gone.
I moved it all around and couldn't get any other reading except 14.0 deg.
the next morning I got it to read 4.5 deg. desired 6.0 actual, this is when I started to replace the cloudy fuel with something better and it runs ok but not the best I've had it
and then there's the cam lobe sensor fault.
Could it be the residual watery diesel keeping that sensor from reading?
Does it do an 8 count and stay off? but restart and work?
I've seen alot of strange behavior since I filled up for my trip.

Edited by: quantum mechanic

I believe this post was made right before he diagnosed a faulty Optic Sensor, Which he knew was already failing, and the 'bump' did not affect its longevity whatsoever.

Actually I had knocked the ECT off it's connection again. It will make your timing go to 14*.

[QUOTE=Texas Diesel Guy]


I just thought I would start a new thread to in case anyone wanted to know a little more about what really makes these pump tick, and eliminate a lot of the misnomers and myths associated with this system. So first, lets start off with the basic.


DS4 831-5XXX


(D)istrubuter Style, (S)olenoid Operated, (4) Plunger, (8) cylinder (31)mm plunger pump


Basicly its a rotary pump with a fuel solenoid in the rear of the pump that when energized, pushes the poppet valve closed to start injection, and opens to end the injection.


Optic Sensor: is locked to the cam ring and advances/retards with it. reads 2 tracks inside the pump that rotate with the drive shaft.


Lo Res track sends a cam pulse to the computer, that sends voltage to the PMD to close the Fuel Solenoid. It is also used by the PCM to measure timing relative the the Crank Pusle so the stepper motor can be adjusted to provide the desired advance.


Hi Res track is nothing but a counter. The computer takes several inputs (throttle postition, engine speed/temp etc. and resistor value) and converts that to a number of hi res counts for the fuel solenoid to stay energized to give the desired fuel delivery (Pulse Width).


[] Lo Res / Cam Pulse.... &nb sp; &nb sp; &nb sp; &nb sp; []


|||||||||||||||||||||||||||||||||||||||||||||||||| |||||||||| ||||||| Hi Res Track


(1 )(2 )(3 &nbs p; )


( Pulse Width )


_________/lobe begins....peaks....and ends\____________________/


Hard to draw a cam profile with ASCII, but just imagine a cam lobe over the words there.


1) Cam Pulse sent to PCM, which signals the PMD and energizes the Fuel Solenoid, which starts to close. Duration here is approximated and will vary with engine speed (longer distance at higher speeds) and Closure Time (amount of lag between this signal and the fuel solenoid actually pulling closed). The computer also starts counting hi res pulses here until it reaches the desired count to end injection (Pulse Width).


2) Fuel solenoid is closed, but injection has not begun, Rollers still ride on flat between the cam ring lobes. Duration again is approximated. This gap is needed to ensure that variations in CT do not cause uneven start of injection events.


3) Start of Pumping: Rollers begin traveling up cam ramp, plungers are forced together and fuel is sent to one injection port. now this Duration is determined by basicly 3 things, calculated by the computer: throttle pos+other PCM inputs (temps etc)+resistor value. Now, Resistor value works like this. The PCM reads its value on startup and treats the 1-9 resistors as if they were -4..0..+4. That tells the computer that it needs to add or subtract X hi res pulses for the pump to deliver the appropriate amount of fuel which is what the pump is calibrated to.


thats the basics, now for the theory.


if you move the optic sensor slightly towards the oncoming ramp of the cam ring and lower the resistor value, you will get the same (1) it does not affect closure time, a shorter (2) and the pumping range (3) will only be slightly longer, and the total PW will be shorter. but now the pumping event will start slightly earlier (advancing timing ever so slightly) and providing more effective pumping time from the same pulse width, which is why the dropped resistor is needed, to compensate partially for the added fuel delivery by shortening the duration. Assuming the optic sensor i

Hmmmm...pictures...I'll see what I can do to help

This is a DS-4, the low/high res optic is under the top cover.


http://www.dieselplace.com/forum/uploads/quantummechanic/2004-11-11_202606_50681.jpg


The F sol in the head of the pump.


http://www.dieselplace.com/forum/uploads/quantummechanic/2004-11-11_202819_5068.jpg


Driver removed.


http://www.dieselplace.com/forum/uploads/quantummechanic/2004-11-11_202917_stepper.jpg


This is the stepper. It rides the passengerside of the pump.

thanks for the pics QM, but im still lost.... what is rotating on the assembly?


I guess I'm looking for some training material that the GM diesel techs got that gave goood cut away and exploded diagrams...lol Does such material exist?

Ok


The cam and crank rotate via the timing chain and the internals of the pump, bolted to this through the oil fill, rotate the internals of the pump which builds the hydrolic pressure to achive the 1200-1500 psi injection line pressure. When you loosen the external three bolts and move the pump left or right you are rotating it, if only a degree or two.

ooooh ok, so the engine's cam has a gear that engages the internals of the pump forcing the pump's internals to spin.


so the optical sensor is keeping track of two sets of marks on the engine's cam and relaying that to the PCM?


Im still not entirely sure what moving the hi-res optical will do when you leave the PMD resistors alone. From my understanding the resistors just adjust fuel trim across the rpm band....


Now if all of the above is true the desired timing is physically what - how far over the pump is rotated in relation to the optical sensor or the cam or both? And actual timing is the degrees before/after top dead center the injectors pop?

The Data disk inside the pump that spins with the pumps rotor has white and black marks imprinted into it, and at one point on the disk it has 8 special marks. The ramp that TDG shows in his 2D graphic is a conceptualization of the special marks and this is the part of the disk that the Optical relates to TDC and compares to the CPS for timing control.


Moving the optical inside advances or retards timing in relation to the data disk. The calibration resistor is able to make up for differences in coil windings so all pumps can be emissions calibrated to within a few mm3.

The Optic Encoder wheel, of stainless steel, is attached to the Inj Pump drive shaft.


This shaft is driven by 1:1 timing gears off the camshaft, which is driven off the crankshaft by 2:1 timing chain sprockets - IP shaft rotates at 1/2 crank speed.


1deg of IP timing = 2deg crank timing - 11deg IP stepper advance = 22deg crank advance.


Encoder wheel has laser-cut slots for timing measurement - one for each cylinder, or 8 slots in 360deg, and 512 slots, 64 per cylinder just inside circumference diameter.


Slot for #1 cylinder is 7.03deg wide, slots for #2 - 8 are 2.817deg wide, at a smaller diameter inside the 512 timing slots.


At 512 slots per 360deg rotation - 1.422/deg - these allow PCM to determine actual position of shaft by 64 slots per cylinder.


#1 - #8 cylinder-timing slots are compared to crankshaft rotational position via the Crank Position Sensor - PCM can monitor actual Top Dead Center position for machining tolerances and timing-chain\sprockets wear.


The ~7deg wide slot at #1 is to measure for +\- 2.5deg TDC Offset and allow for adjustment.


Factory timing is +3.5deg with -0.5deg TDC offset.


And, with the ~3deg slots for the other cylinders, allows the PCM to measure inertial differences cyl-to-cyl at idle.


PCM uses this info to correct for various loading, maintaining smooth idle and correct idle rpm.


A\c loading, shifting in and out of transmission gear ranges are compensated for to maintain smooth idle.


Cylinder variances can be from low compression, worn\weak injector, leaking valve(s), etc.


When PCM cannot compensate, a History DTC is set for Cylinder Imbalance for each cylinder.


TDC Offset adjustment, some have stated, is to put Timing Stepper Motor in middle of it's mechanical travel limits, which would allow +\- 5.5deg IP timing adj (11deg), for +\- 11deg crank offset (22deg).


However, once IP and crank timing is adjusted for - say + 8.5deg base, or Desired - it only advances from that value - never retards from there.


Desired\Actual timing may advance from +8.5deg and settle at +19deg at 70mph level cruising, then "retard" back toward +8.5deg as loading changes - up-hill - but at no time have I ever seen ( IP adjusted and locked to) +8.5deg Desired\Actual retard toward +3.5deg under any type of loading.


As you can see, if TDC Offset is an adjustment to put the TSM in the middle of it's mechanical travel, it would be then be banging against it's most-advanced limit, to achieve +19deg advance, with no hope of any further advance.


+19deg is cruising advance at ~2000rpm - what about kicking it into passing gear, rpms increasing to 3000rpm as vehicle speed increases - advance mechanically limited to only +19deg? Not good.


I'm working towards something, based on what I've observed, but I'll leave this open here, if Texas Diesel Guy or DieselPro would like to offer first-hand legitimate training-based input.


Pro or con is cool, either way.Edited by: gmctd

I see what your saying, and I've pondered the same thing myself. A great deal of the advance range is wasted in below minimum advance range, so why not move some more of that to the top end. Optic sensor will achieve this partially, as it increases timing across the board, this was also my plan when I installed a #1 resistor to trim fuel quantity back, and allow me to move the optic further to obtain even more advanced timing. Works great so far, but going more than that would take a reflash.

oooooh ok so moving the optic sensor bumps the advance/retardation of injection across the WHOLE rpm band because you are fooling the computer. Where as just rotating the IP will only change the base timing before the computer gets to changing things according to load right?


Why would you want reduce the fuel trim with use of a lower resistor?





How does a worn timing chain affect overall timing? I assume it would retard the timing across the RPM band without the PCM knowing about it, so you'd need to give the optical sensor a slight nudge right?Edited by: Bumpin' Yota

Bumping the optic sensor advances it relative to the camring, which means it starts pumping fuel earlier (advanced timing) and since the duration is unnaffected it pumps longer (increased fuel delivery).


A worn timing chain will really only affect your camshaft timing. The computer adjusts pump timing relative to crank timing, which compensates for play in the chain. The reason you have to set TDC offset and base timing is to get the pump in a position where it can reach full advance and retard range.


The calibration resistor is determined on the test bench to fine tune fuel delivery. Using a lower resistor means slightly less over all delivery, but allows me to go further with the optic advance to get the fuel up and more advanced timing and it also keeps the PMD energized in shorter pulses so it will last longer. So far, my plan is working, I've got a used 2nd generation PMD that hasn't missed a beat yet.

Ok.


So, just advance the pump housing X* after you have base time set to your liking? How far in can you force the stepper in before the SES lights up?

Ok now after replacing the pump and getting it started how does one go about getting it running correctly with the timing if you dont have a Tech 1 cartridge to do the timing offset learn proceedure?

I responded to your other thread T4CT.

Forcing the stepper motor up would give you too much advance all the time and won't help anything and will trip SES light quickly.