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Discussion Starter · #1 ·
Just got this one a few weeks ago and i'm catching up on maintenance. It starts to stumble,some little backfires thru the exhaust. Sometimes have to floor it on hot restart(as if flooded). I remember when I replaced the air filter and flipped the lid,the underside of the lid was damp with fuel.
I jumped the terminals to get a malf code and got a 42, indicating ignition probs. I've replaced the tune-up items of cap/rotor, plugs/wires and also the ign module that's in the distibutor. It seems like a fuel prob,despite the malf code. when I rev thru the problem,the ck eng lt comes on and the problem goes away until i shut it down and it resets the ck eng lt. Weird!
Any input would be appreciated....
 

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Obviously it's a 2.8 GM V6.

Sometimes you'll throw another code in sympathy with deeper problems.

One problem I had with mine, was all of a sudden it was running bad and quit. I discovered that the Engine Coolant Sensor (ECT) on the intake manifold was bad. It had an extremely high resistance, which the ECM interprets as a very low temp. Then it goes to extreme rich and the rig either runs terrible or quits.

If you unplug the connector (front part of the intake, sticking straight up), and it runs better, the sensor is bad. Do a resistance check of it cold, and warmed up. There are resistance charts for the various GM sensors which will tell you if it's in spec or not. If it's not the ECT, maybe check the MAP sensor (a bad one can cause backfiring), along with your O2 sensor and maybe even check for timing chain slop. Erratic timing could conceivably throw a code although not very common. If the timing bounces around a lot on the timing light it could be an indication of timing set wear. Move the crank pulley back and forth while watching the distributor rotor and you'll have a pretty good idea of how much slop you've got in there.

Here's a few sites with good EFI systems info:

http://www.kemparts.com/TechTalk/tt13.asp

http://www.borgwarnerbrand.com/techtips/gm.html

http://clubs.hemmings.com/clubsites/fie ... AP/MAP.htm

http://www.syty.org/old/d&e-lackpower.html

http://www.goingfaster.com/spo/tbi.html

http://www.techweasel.com/articles/troublecode/GM.htm

http://www.sonic.net/~mikebr/efi/plots/ ... s_adc.html

http://www.niehoff.com/techtips/techtipidx.html

Anyway, hopefully these will point you in the right direction. Good Luck and let us know what you find.........ed
 

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2.8 TD's don't have distributor caps, ign modules, spark plug wires or spark plugs, of which he stated in his post that all of those items had been replaced. :roll:
 

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Ed Mc. said:
2.8 TD's don't have distributor caps, ign modules, spark plug wires or spark plugs, of which he stated in his post that all of those items had been replaced. :roll:
That and he's from OK City and ISUZU hasn't had diesel Troopers here since the early-mid eighties :wink: (See thread title)

When does the 42 set? When you rev up and the CEL light comes on, immediately turn the truck off and then pull the code (if you haven't already....) As Ed Mc said, sometimes you can have a cascading of Codes and 42 was only the last one stored. You might also have a screwy EGR and/or O2 sensor thing going on too making the ECM overcompensate or something......

Code 42 is an error in the EST (Electronic Spark Timing) system and the helm manual has a through assessment tree of this code - can someone scan this in and post it. Although he says he replaced the ignition module so IF that was flaking out it should have solved the problem and it didn't.

There is also a module on the p-side fenderwell that the spark-knock sensor plugs into that also may be suspect, but I'm betting its a wiring short.

First thing I would do is disconnect the EST from the ECM and manually check the timing JUST to make sure the chain hasn't jumped.

Then I would start taking Ohm's readings to see if something is grounded out. The ECM itself is also suspect in this case according to Helm.

If you plan on keeping this truck and/or wrenching on it yourself regularly, I would HIGHLY recommend getting the full service manual from http://www.helminc.com DO NOT rely on Chilton's or Hayne's to diagnose something like this or you will wind up excessively frustrated and cussing like a sailor :D .

Good Luck.

Cheers,
 

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Discussion Starter · #7 ·
I did have an '86 TDi Trooper a few years ago and do miss... :?

Thx for the diagnostic ideas folks. The ECT idea will be checked first,since the prob seems to appear after warm-up. The tach fluctuation is really odd as is the prob clearing up after the cel triggers.
I appreciate the feedback and will report back after I check it out. 8)
 

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Discussion Starter · #8 ·
Ok, good news! I got a coupon for a free computer diagnostic from my bank to be used at a local GM dealer. They checked it and concluded it was the coil and the coil malf had taken the ign module down with it.
Cut a ck for $55 at Auto Zone and it's all good. :)
It will be nice to see how the mileage improves. the throttle response is crisp and peppy. Gotta keep my foot out of it. Under WOT it freely revs to 5500 and shifts smoothly.... :D
 

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Now that's werd :?:

I was always under the impression that the coil either worked, or it didn't so the engine wouldn't start if it crapped out.

So, what you're saying is that you originally replaced the ignition module, not knowing the coil was bad?

And now you've replaced the coil and the ig mod because the first one you put in went bad because of the bad coil?

Just want to make sure the sequence is right.

That's awesome your ride is pack up to par - CONGRATULATIONS - It's a great feeling to make a repair and have it all work! 8)

Cheers,
 

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Discussion Starter · #10 ·
Yeah, I know what ya mean. I had noticed it didn't start until it fully warmed up, and I had worked on a motorcycle before that died after 10min due to the coil. Mr Goodwrench said something about feedback thru the coil... :eek:
 

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Discussion Starter · #11 ·
Update: The same malf has returned, typically under a load, on the highway,but rarely in the city. That's been going for a few weeks and as of today it's getting bad in town.
Good news is the parts are under warranty.
Bad news is the question of what is the underlying cause. LTC Don mentions a module on the p-side wall relating to the anti-knoch sensor. I'm wondering what all would influence the tach reading since that is the first sign of the problem.
For now I'll r+r the coil and module again to buy more time to t-shoot the issue.
Damn! Shoulda kept the turbodiesel....
 

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Discussion Starter · #12 ·
Ok, coil and module replaced again and all is well for now. I got the GM part# from the module on the fenderwall and it's a electronic spark control module. That is what I'm looking at as a possible underlying cause.
I can get a new one from GM for $97, or from Isuzu for $67...
Also found a good website for the V6: http://www.60DegreeV6.com
 

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You can probably get one real cheap out of the junkyard, just look for a TBI S-10 of similar vintage.

Note that there is a big bundle of wires grounded to one point on the block, beneath the pssgr's side exhaust manifold. Included in this bundle are the grounds for the ECM and also the ESC module. If they aren't properly grounded you'll have all kinds of strange behavior.
 

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Discussion Starter · #14 ·
Well, I replaced the coil and ign module fri, and still had some of the problem show up on the highway. NAPA was able to source the esc module for $53 and will have it this week.
Thx for the ground tip! I'll check it out...

Still shoulda kept the TD.... :roll:
 
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