The wife came home lastnight w/ the car, was sputtering shaking, running like crap. Had a bad miss and the ses light flashed at her a bunch of times. I pulled the code this Am and found a #4 cylinder misfire. I replaced the plugs, and wire boots, and checked the coils. The coils read in spec. I fired the car and she ran smooth as a top :). Took it out for a test drive , and it started sputtering , bucking, missing again, and running like crap . Threw another #4 cylinder misfire at me. Limped it home , checked the coils again , again they are in spec. Cleared the code, tested all 4 injectors. They are fine. Tested the injector harness, it is fine. All injectors getting signal and working properly. Re-fired the car, and it sat @ a smooth idle for almost 30 minutes. No issues. Put it in gear for a test drive, rpm's drop, misses start car runs like crap all over again. Any way to test the ignition control module before I throw another $130 out the window? If I replace it and it isn't the problem I'm gonna be pissed. I didn't mind the plugs and boots, they were bad and needed replacing anyway. I'm not a big fan of throwing money at a problem to fix it, and it seems that whats these cars are all about???? could be:runaround: could be:runaround: or it could be :screwy: !!! This car had been nothing but a headache . I'm a lifelong GM guy, and I can't say I'd ever buy another GM product? RANT OVER :)

Its pretty hard to test the ICM fully with out the proper equipment. A lot of part stores can test it for you though.

So As long as the primary and secondary resistance is within spec you know the coils are good. I think primary is approx .4-.8 ohms and the secondary would be 4000-8000ohms.

You can also check the trigger signal with a light probe.
Attach it to a positive soarce, then probe the two negative terminals on the ICM and turn it over.
If you dont get a signal(light flashing) on one or both then your crank sensor would be the culprit, Id test that too. :grinyes:

One last thing double check all the injectors wiring from the main harnes to the injectors. These are known to crack and get shorts causing misfires, even on the newst GAs. :disappoin

Hope that helps!

Thanks for the reply. I have tested the fuel injectors, and the harness. They all seem to be getting proper signal , and the injectors all pulse and test ok. I didn't notice any cracks or wiring problems. I will look more into the cranksensor.

As with the injecters, you could get a signal they are firing and they still be bad.

Did you measure the resistance on these as well ?
Resistance should be between 1.95-2.3 ohms.
If not its a bad injector.
Also double check the grounds for the injectors, this will cause misfires too. ;)

Miss seems to have changed over night. It is now missing constantly ,at idle as well as underload. And the code has changed from #4 missfire to a #1 missfire. I'm leaning towards the ICM now more than ever. I could see a bad injector/connector on #4 cylinder, but not #4 and then #1. I'll pull off the ICM bring it in and see if they can test it, if not I'll just pick one up.... I hate to do that but , the signs point to that being the problem :)

I think your assumpsion is correct here. If the ICM is over 5-6 years old it probly needs replaced.

The problem with these engines(and others built like it) is the coils and ICM are inside a little oven thats very hot most all the time.
So all that exteme heat just kills the electronics inside, slowly cooking.

OK, just to follow up. I replaced the wire boots, and the plugs. As I stated earlier (or maybe I didn't ) I'm a cheap buggar. I don't like throwing money at guesses. I figured if i'm gonna guess I'm gonna guess and try to save money also. I went to the salvage yard and plucked a whole top cover, coils, and ICM for $75. I got home threw it on and it runs better than it has since I've owned it. So it was indeed the ICM. The only thing I noticed, was a slight stumble just off idle when cold. It has always done it though, and it goes away after the first 2-4 minutes of run time. Doesn't come back until the motor is stone cold. I'm thinking I'll clean the IAC this weekend and see if that helps it. Next oil change I think I'll do an o2 sensor as I'm sure that is still original. Now tires and the heatercore, and my freecar will keep going strong.
Thanks again for the help, it is nice to have a forum like this to go on to share opinions and give info/advice,
Jamie

No problem and glad to help! :cheers:

Since this is a recent thread I thought I'd piggy back on your question with my own:

I seem to be having the exact same problem as you. I bought the car misfiring badly, pulled the plugs to find #3 missing the inner electrode. I replaced all the plugs, and removed the coil housing and ICM from the cover, put them in the car, and it seemed to run smooth(it was late and I was tired, so I could be wrong). When I hooked up the cover however, it went back to misfiring (although ran better with the new plugs). The one thing that sticks in my mind is that one fo the cover bolt holes had a ground strap connected to it, and it was just dangling there, not connected to anything. Did yours have a ground wire connected, and where did it go to? Pictures would be most helpful..

Jonota

The ground strap on the cover connects to one of the cover bolts and then goes under the white plastic coil housing I believe there was a second metal ground strap that runs the length of the plastic housing to ground both coils. The other end just kind of hangs out of the coil cover.
http://img3.imageshack.us/img3/5821/coilcoverga003.jpg (http://img3.imageshack.us/my.php?image=coilcoverga003.jpg)
http://img3.imageshack.us/img3/coilcoverga003.jpg/1/w640.png (http://g.imageshack.us/img3/coilcoverga003.jpg/1/)


HTH,
Jamie

That does and it doesn't. I found another online picture that showed me what your picture does, and I hooked it up that way (also got another housing). Still have the same problem. Now I DON'T have another metal piece grounding the coils... so if there is one I need to know. Could you get a pic of that???

Thanks for the post!!!

Jon

Yeah gimme a sec to pull the cover apart ..BRB lol

ok , my mistake, that strap just grounds the cover. It does not connect anywhere to the coils. Just kind of pinched there between the plastic and metal housing. Did you clear the codes after you replaced the cover? Have you check your injectors yet?

Thanks for the quick reply!

Things done:
Plugs (one was broke, replaced, haven't gotten "#3 misfire" since)
Checked and wrapped stubby "boots"
Replaced coil pack housing
Coil primary to primary and primary to secondary resistance checks (0 and open respectively, both coils)
Scanned w/ HP Tuners (I tune on the side)

When I scanned it was most recently, the only "new" code was Random Engine misfire. Only things in the generic parameter list that looked weird was the ignition timing, which jumped VERY erratically between 20 and -3 (ish). I have fuel smell out the exhaust (medium strong), which I attribute to the misfiring and non-burning of fuel. Researching recently leads me to try next:

-intake manifold leak check: spray some wd40/carb cleaner near intake manifold, check for flucuations in how engine sounds
-MAP sensor vacuum leak: I saw something about a vacuum line to this going bad, but I could't immediately locate it....and my scan showed that it held lower 40's kPa at "idle" and 56 kPa in "drive/reverse", which is low bad not THAT low. (where's the MAP AT?)
-ICM swap with known good module
-coil swap (not likely since it seems to be jumping cylinders)
-fuel pressure test
-injector resistance check/noid light check/stethoscope
-disconnect exhaust manifold, run, check for change (plugged cat)

Right track/more information??

Jon

Thanks all!!!