88 2.5 L4 Ignition issue (Page 1/2)
Mark_j JUL 06, 12:56 AM
I have an ignition issue with the 2.5 L4 DIS ignition.

Initially I was working to correct a missing problem under load. Typically this is a sign that the MAP sensor is starting to go out. I had no codes so it hadn't died yet but since I keep a spares around I went ahead and changed it. No dice. Problem still remained. Since I hadn't changed plugs and wires for a few years I went ahead and dug into the spare parts reserve and did the whole works.

All parts were new:

Plugs
Wires
O2
Coils
ICM
Crank Pos

The old crank sensor had a crack in the barrel - changed for new.
ICM replaced. Used Arctic Silver to facilitate thermal transfer from both the ICM and the coil shield. Everything was installed and dielectric grease used as needed where applicable. I didn't clear the ECM but didn't figure that would make much of a difference.

Started right up after all was re-assembled. Ran no-load for about 15-20 minutes to make sure it was up to temp. Shut down engine to finish getting the air filter and a few other small things re-installed. Came back to it a cpl hrs later to do road test. Started right up but as soon as it was put under load (put it gear and let clutch out) it died and would not restart. Acted like I had no spark.

Couple days later I changed out the new ICM for the old one, left everything else as I had it, cleared the ECM and re-started. It ran no load for about 5 minutes then it shut down and would not re-start.

So the question is, after following the FSM instructions and being very methodical about this, what did I miss?
Dennis LaGrua JUL 06, 07:44 AM
First thing to check is to verify if you are getting spark. Use a spark tester or a timing light to check. If no spark, the ICM or a coil may be bad. If you have spark then move on to checking the fuel supply.
skywurz JUL 06, 10:07 AM
Did you also remember to swap the shield? See ogres cave DIS ignition. Maybe you got a bad cam sensor out of the box.?

[This message has been edited by skywurz (edited 07-06-2022).]

theogre JUL 06, 10:36 AM
⚠️ Do Not use Arctic Silver or any other Heatsink/Dielectric "Grease" w/ DIS ICM. They will not flow properly for a huge area to spread out.
Silicone Grease has same problem as HSG. Si Oil is part of many HSG that "dries out" and using just that will run out fast.
⚠️ Never use "Liquid Metal" that Eats Aluminum!

Use a small amount of Permatex Brake Grease or Nothing. GM installs them Dry but Duke's DIS location make easy to get water and then "rust" in the gap and PBG stops water and act as HSG w/o particles that can cause problems here.

Do Not use anything on the Shield for the Coils. You Don't want Heat from the Coils transferred to the ICM.

Pull the console to allow more air to cool the ECM. Very Careful Use inverted canned air as freeze spray may work too. If helps some to a lot then = "Dead" ECM.
See my Cave, ECM Heat

Check Fuel Pressure. Need an adapter. See https://www.fiero.nl/forum/Forum2/HTML/146121.html
Pump or other things can F'ed pressure after running, stay running then park and die, and more.

For DIS Duke and some others... While ECM has no control or feedback of EGR, any problems w/ EGR can cause "Ignition Breakup" under load because ECM PROM is written for proper EGR function.

Note: If Heater Joint under the intake manifold is leaking... Coolant is very conductive and can cause problems for the DIS brick.
See my Cave, Heater

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

Mark_j JUL 08, 11:21 PM

quote
Originally posted by Dennis LaGrua:

First thing to check is to verify if you are getting spark. Use a spark tester or a timing light to check. If no spark, the ICM or a coil may be bad. If you have spark then move on to checking the fuel supply.



Since it actually ran after I did all this, I don't think spark is totally the problem unless the ICM did or does a thermal shutdown. I've checked it with an inductive timing light and although it is hard to see it appears that I'm getting some spark. As far as fuel It was running fine before all this and unless the fuel pump is fixing to go tits up (it's only about 4 years old and when it died last time it was just dead not any warning) of course I can check it again but for now it sounds like it always has and pressure (from the sound of it) come up like normal..

[This message has been edited by Mark_j (edited 07-08-2022).]

Mark_j JUL 08, 11:29 PM

quote
Originally posted by skywurz:

Did you also remember to swap the shield? See ogres cave DIS ignition. Maybe you got a bad cam sensor out of the box.?




It's part of the ignition brick, why would I not transfer it? Bad crank sensor? Possibility but then it wouldn't run to begin with if that was the case.
skywurz JUL 08, 11:38 PM

quote
Originally posted by Mark_j:


It's part of the ignition brick, why would I not transfer it? Bad crank sensor? Possibility but then it wouldn't run to begin with if that was the case.



You would be surprised how many people don't.
Mark_j JUL 08, 11:57 PM

quote
Originally posted by theogre:

⚠️ Do Not use Arctic Silver or any other Heatsink/Dielectric "Grease" w/ DIS ICM. They will not flow properly for a huge area to spread out.
Silicone Grease has same problem as HSG. Si Oil is part of many HSG that "dries out" and using just that will run out fast.
⚠️ Never use "Liquid Metal" that Eats Aluminum!

Use a small amount of Permatex Brake Grease or Nothing. GM installs them Dry but Duke's DIS location make easy to get water and then "rust" in the gap and PBG stops water and act as HSG w/o particles that can cause problems here.



I actually used the little packet of thermal grease that came with the new ICM and spread it acrossed the entire surface of the ICM and from what I could tell when I changed out the part for the original ICM it had made full contact with the surface. But if that stuff isn't right then I'll clean it all off and use PBG.


quote
Originally posted by theogre:
Pull the console to allow more air to cool the ECM. Very Careful Use inverted canned air as freeze spray may work too. If helps some to a lot then = "Dead" ECM.
See my Cave, ECM Heat



That would be a recent development and besides wouldn't the ECM give me an indication of something like that when put in self test mode?


quote
Originally posted by theogre:
Check Fuel Pressure. Need an adapter. See https://www.fiero.nl/forum/Forum2/HTML/146121.html
Pump or other things can F'ed pressure after running, stay running then park and die, and more.



Again, I'll check it, but as I said before, everything was fine until I changed out the ICM.


quote
Originally posted by theogre:
For DIS Duke and some others... While ECM has no control or feedback of EGR, any problems w/ EGR can cause "Ignition Breakup" under load because ECM PROM is written for proper EGR function.



Ok, that is a new one on me.

Though it might make sense. According to my records, I changed the EGR some 15yrs ago when I first bought the thing. And the reason I did that then was not because it ran poorly but because I had an Olds Cutlass Ciera with a 2.5 that loved to trash EGR valves. Probably put 2 of them on that thing for the 10yrs I owned it.


quote
Originally posted by theogre:
Note: If Heater Joint under the intake manifold is leaking... Coolant is very conductive and can cause problems for the DIS brick.
See my Cave, Heater




Not a chance. I'm a fanatic about coolant/fluid leaks and would have caught that one immediately. It still annoys me that I haven't been able to keep the valve cover from oozing oil into the plug sockets. Had a buddy who used to work on Navy P3's with the turboprop engines and his favorite saying was "if it ain't leakin oil, it's 'cause there probably ain't none in it".

The Duke is sorta like that.

Anyway, thanks for the info. I'll let you all know how it turns out once I dig into it again.

[This message has been edited by Mark_j (edited 07-09-2022).]

Mark_j JUL 09, 12:05 AM

quote
Originally posted by skywurz:


You would be surprised how many people don't.



Nothing surprises me as far as automotive stuff goes. I've seen over the years some real, if you'll excuse the expression, "redneck engineering' that makes one wonder how they get it to even work.
Dennis LaGrua JUL 09, 05:46 AM

quote
Originally posted by theogre:

⚠️ Do Not use Arctic Silver or any other Heatsink/Dielectric "Grease" w/ DIS ICM. They will not flow properly for a huge area to spread out.
Silicone Grease has same problem as HSG. Si Oil is part of many HSG that "dries out" and using just that will run out fast.
⚠️ Never use "Liquid Metal" that Eats Aluminum!




I've used thermal conductive grease on the plate where the ignition module mounts without problems.