OK Guys... I come from the world of big diesel engines... Fairbanks Morris.

I love diesels, and I love 2dr tahoes, so I bought one.

I am not happy at all with the stock performance of this engine.

I believe my biggest problem is the PMD/FSD.

The installation of boost and pyros should help in diagnosing my jitters.

But aside from that, and getting back to the subject, what is this business about boost fooling?

I understand what you are trying to do... but how are you doing it?

Does anyone have any pictures of where exactly they tapped into the MAP harness?

And what was the purpose of "tricking" the BARO sensor?

If anyone has a schematic (even something on a bar napkin) could you post it... I am great with AutoCAD and can turn it into a drawing we can all use.

On one last side note, last one I promise, if anyone has a cooked PMD/FSD they would like to donate?

I am looking for one for my electronics class.

It is just a DC analog device, so I am thinking I can reverse engineer it and make something a little less "troublesome" out of it.

Of course the supplier will receive a modded version as a token of my appreciation.

Let me know though...

'95 2DR Tahoe, 6.5 TD 4L80E, Stock...stock...stock...

Use the SEARCH function, and spend some time reading - it should get you up to speed in the quickest manner.


Btw - are we talking big Fairbanks Morse Diesels here, or the Morris hit-and-miss engines from early last century, sometimes called 'poppin' johnnies', from the John Deere versions?Edited by: gmctd

I did this real quick.


This is how I would add a 10K pot. switch.


http://www.dieselplace.com/forum/uploads/ZD5_Boostswitch5.jpg


Switch the wires if it does't work.








EGR? Plug it. Put 5-10K ohms off the Baro to bring it closer to the lower MAP reading for no codes for Boost sensor out of range.


I have an FSD that started stalling a '96. Edited by: quantum mechanic

GMCTD,

Yeah, the "big" ones... if you consider an 8.125 in bore big. To be specific I specialized in marine diesels... The FM 38ND8-1/8. It only developed about 1200 hp, but the ft/lb were off the charts @ 720rpm. They typically ran Woodward UG-5 or 8 series governors, so you just set the rpm, load limit, and stand back. Really fun to wrench on too. Are you familiar with these engines?


QM,

Thanks for the sketch. I will clean it up (not too much though, it's pretty clean already http://www.dieselplace.com/forum/smileys/Clap.gif ) and post it as an html picture. What I gather from your diagram is that you really were looking for 20k ohms of resistance. Is that accurate?

I don't use the full pot. with the fixed. The pot. is there for "limited" use but the same as 20K fixed, yes. without 5-10K on the baro 20K on the MAP will set a code for sensor out of range.


I didn't label wire (A) as 470 blk, E14(ECM) sensor ground wire (B) 432 Lt Grn, B13(ECM) MAP signal wire (C) 474 Gry, E14(ECM) 5v reference.

Been in the crankcase of a few, where the sump is the floor of a 3-4 story building - entrance is a standard sized door cast into the crankcase wall.


Pistons about size of 35gal barrels, about 100rpm, or so - massive.


I see the problem, QM - you're config'ed as a rheostat, varys current.


PCM wants variable voltage from MAP, representing varying pressure.


Mod requires potentiometer config, to offset voltage on B to PCM.


Remove wire from B, 10k pot goes across B to A, wiper goes to wire from B.

edited


Edited by: quantum mechanic

Pot has three terminals, or leads.


Resistor is connected to each end terminal - center terminal is variable tap, or wiper.


One end terminal connects to A, opposite end terminal connects to B.


Connect terminals such that clockwise rotation increases Boost.


The wire that was originally on B, to PCM, connects to center terminal, wiper.


This allows wiper to adjust to any voltage between ground (A) and pressure-derived voltage on B - effectively offsets pressure that PCM reads, allowing more Boost.Edited by: gmctd

One more look.


http://www.dieselplace.com/forum/uploads/EF3_Boostswitch3.jpg


Would this reflect what you said?Edited by: quantum mechanic

You got it.....


Reverse pot leads to A and B if necessary to get CW Boost increase.


Rotate pot shaft to ensure wiper is closest to B initially, which will be oem Boost.


Rotate shaft towards A to increase Boost.


Go too far, and you'll get DTC for sensor out of range condition.Edited by: gmctd

Before, I was resisting volts and increasing boost but I had it wrong and right in that it works (I'm used to this, learning by doing has a price). I will change to this set up and scan it to see what I get.Edited by: quantum mechanic

I am glad I asked a somewhat redundant question.

I will revise my drawing before I post it.

One quick question though...

Have you considered using the volume knob (just the plastic piece) from a factory radio to resemble an oem appearance of the boost "dial"?

Just A thought.

I will finalize my drawing and add a bill of material.

Should be on later this evening.

---Does anyone have any leads on the cheapest source for FSD/PMD's?---

The original hookup you used does essentially the same thing, just requires more overall resistance in the loop.


You may even want to go back to that - I was having trouble getting why it required double resistance value to work

.

---Does anyone have any leads on the cheapest source for FSD/PMD's?---


about 250.00 from my dealer here in S/W OK should be bout the same elsewhere. Unsure of anywhere non dealer to get them without buying a kit. BUT I'm sure someone on here does.

When you guys get this fooling figured out could you please let me know, i only want to cut once. http://www.dieselplace.com/forum/smileys/HiHi.gif

Here's a way Whatnot showed me but I've never tried.


http://www.dieselplace.com/forum/uploads/1BC_Boostswitch4.jpg


I am going to try a fresh pair of these as well.





http://www.dieselplace.com/forum/uploads/AC8_exhaustdonut.jpg


Edited by: quantum mechanic

That config sets Boost at a fixed predetermined level, based on the ratio of the selected R values.


Dial your pot in for 10psi Boost, measure the resistance between wiper and A, get a fixed value to match.


Measure the resistance between wiper and B, get a fixed value to match.


Solder it up, hide it, and forget it.


Not nearly as impressive to the ladies as an adjustable control on the dash, suitably Dymo-labeled, which you mysteriously reach out and tweak every so often, while tapping on the Boost gage with a fingernail, and muttering things like "if GM only knew about this little trick Isuzu wouldn'ta stood a chance".


http://www.dieselplace.com/forum/smileys/Wink.gifEdited by: gmctd

It sets the boost range code at 1.15 v. It's at 99.7% WGDC at 1/4 pot.


So, now I have more switch than I can use. How should the baro be resited. Would whatnot's configuration of the appriate fixed resisters on the baro keep the boost range code from coming up? I'm still using one 5.6K on the baro's "B" wire.

OK, i have my pot switch now, now whats the correct way to hook this thing up? I thought the left or right pole was used to resist by turning the knob left or right depending on which one you hooked up to? From what i understood before you didn't use all 3?


OK, i just took my ohm meter and checked this switch and it works exactly as i just described, so forgive me for being silly but why would you hook up all 3 posts? I believe i have the same one as QM from radio shack. Linear taper pot, 500 VDC - 0.5W 10k, part #271-1715 ($2.99 Canadian)Edited by: CanadianRigger

There's two ways. The first drawing shows how to wire the switch as a reastat(I'm editing it as I write this). It will give you a 1-3 psi gain over stock when your using the fuel pedal. The second way is as a true potentiometer. You use all there poles because your potential is between Ground (infinte Ohms) and the "B" wire's stock signal. This will give you full boost(sustained 15 psi) at 1/4" turn and set the boost range code at 1/2 turn. basically, a sensitive version of the first way.

Guys - a switch is off-on, like the light switch in the house and in your truck.


This is a variable device - a resistor, called a potentiometer, like the old volume and tone controls on a radio or tv.


Some volume controls had switches on them, to switch power on and off.


When the two end terminals are wired into the circuit, the shaft moves a wiper along the resistor, from end to end, varying the voltage on the center terminal from low voltage at one end to high voltage on the other.


In this case, from ground, or zero, on the terminal wired to A, to a voltage determined by manifold air pressure on the opposite terminal, wired to B - something between 0v and +5v.


If the PCM sees 4volts for 7psiBoost, we adjust the pot so the PCM, wired to the center terminal, sees only 3volts, and the PCM is tricked into calling for more Boost.


PCM is happy with what it is seeing, and so are we, cause we're getting 10psi instead of 7.


There will be a test at the end of the class........Edited by: gmctd

So which diagram should i be using for the best results? Sorry, me and this electrical stuff aren't a good combination... lol

Use the center and left posts looking at the knob end, that will make the switch increase resistace as you turn the knob to the right (C). Wiring to the center and right posts will make it work backwards, left to increase resistance (CC).

Use the last diag, where I posted 'you got it'.


With terminals up, shaft toward you, left terminal to A, right terminal to B, center terminal to wire that was on B.


You'll want the end terminals connected such that clockwise rotation increases Boost - crank up the volume means More Power..........


Start off with pot fully ccw, adj slowly cw until you get feel for rotation vs increaseEdited by: gmctd

Seems to me that there will be 1 wire just hanging with nothing hooked up to it, can QM make a better diagram?

http://www.dieselplace.com/forum/uploads/DZE_Boostswitch6.jpg


You can do it like this with two wires or...


http://www.dieselplace.com/forum/uploads/155_Boostswitch3.jpg


Like this with three.


I'm trying out the second way. I set mine on 99.7% wgdc but got the boost range code yesterday. I turned it down just a hair and havn't seen it again.





The thing you need to remember is that your OBDII uses the MAP as the BARO on strart-up, so fool the MAP and fool the BARO. My dad's '96 has the two wire set-up and I asked him to turn the pot. to half to start and then pot. off. and then progressed to full pot. on to start and then pot on. He noticed more boost with more resistance, of course.


On the other hand to achive stock boost, turn the pot. to off and start and leave the pot. off.


Edited by: quantum mechanic

So as i understand it where your pic shows a break in the wires they are actually connected through those points, right? Just trying to be 100% sure before i do any cutting. http://www.dieselplace.com/forum/smileys/Cool.gif

That's showing continuity. I thought it was clearer than crisscrossing them. The three wire pot. would be different for you as well. You would not want it on more than 1/8 turn when you start.


http://www.dieselplace.com/forum/uploads/4AE_pot.switch.jpg


That's a non linear taper so you're seeing 1/3 pot. switch.


Edited by: quantum mechanic

if i wanted something that i could just wire in and leave alone, could i just use 10k on the map b and 5.6 on baro?

Yes, and I could tell you the right values for this way.


http://www.dieselplace.com/forum/uploads/BCA_Boostswitch4.jpg

http://www.dieselplace.com/forum/uploads/ZEF_boost.JPG

Is this what the schematic should look like?

I haven't had much time to play lately so this is taking a while.

Thank you everyone for your input.

QM, so i only need 5K ohms on the green wire, and 2K on the green to A wire? what color is the A wire? how much difference is there between 1K and 5K? i am not familiar at all with this stuff. i hope radio shack will take back the 10K's i bought a while ago.

Steiner,


I would have to measure the two resitance values on my pot.to tell you for sure. I could have the values by tomarrow if Ivan heads on(can you believe this things still here?). The black wire is the "A" wire and is the curciut ground for the MAP sensor curcuit. The values will be something like 2.5K on the "B" wire and 1K on the "B" to "A".


The difference from 5K and 1K is 4,000 ohms resistance.Edited by: quantum mechanic

Whats wrong with plain jane? 10k pot wired like this on mine is good for sustained 10+ psi.


http://www.dieselplace.com/forum/uploads/748_map.JPG

TDG,


That set up is currently working in my dad's 96 and it was work for me untill recently as well. Dash boost guage verified 10+ psi. But it has to be wired right. Ruben complinained as well as CR but I konw it works if hooked up right in a properly running system. With a little variation and cosideration between OBDI/OBDII and EGR systems.