INCREDIBLE upper-rpm misfiring...

[85_305]

wtf is happening? It's only sometimes.. in some gears.. in some conditions. Today, I pinned it in third gear, and there was nothing but misfires at like 4k rpm till redline, I had to let WAAAAY off of the gas and hardly accelerate to get up to speed. It did it when I punced it in the next gear too. BUT.. just a few miles down the road, I dropped to fourth (cruising at 65 or so) and there were no misfires. Dropped to third, and it didnt seem like there were any misfires?
WTF is happening? It gets BAD sometimes :irk:

EDIT: Sorry, it's my '93 Sunbird, 3.1 5spd.


Matt

[85_305]

Nevermind.. a mechanic said it might be that stupid system they put in that automatically cuts out and only fires every other cylinder to prevent over rev

[IsaacHayes]

Huh? Why would the rev limiter affect you while driving??

I'd say it's the CPS or ICM.

[TazMan]

Huh? Why would the rev limiter affect you while driving??

I'd say it's the CPS or ICM.

I was wondering the same thing. Is there an SES light? I had the same problem, and there was no SES light for two days. Eventually I got the light and the code was for the ICM. I changed that and the coil packs for ones I had lying around from my last car and all was good.

[pontiac3100]

well you guys it could be the fact they replaced the pcm with a auto pcm.

but then again...no offense i call bs.
because gm has two rev limiters...on autos that is, the 4k n/p and the 6500rpm rev limit.

so imo theres no way that it could be....

[85_305]

Huh? Why would the rev limiter affect you while driving??

I'd say it's the CPS or ICM.

No he says it's some kinda limiter put in incase you downshift or something too early it will only fire every other cylinder to prevent damage. It did it again today racing a car when I shifted from middle of fourth to third. I was pissed. What is the ICM? I dont think it's the CPS though. How can I tell if it is?

I was wondering the same thing. Is there an SES light? I had the same problem, and there was no SES light for two days. Eventually I got the light and the code was for the ICM. I changed that and the coil packs for ones I had lying around from my last car and all was good.

Nope no SES's. But I will let it be known that the coil pack is not bolted down tightly.. for some reason it's just hanging there.

well you guys it could be the fact they replaced the pcm with a auto pcm.

but then again...no offense i call bs.
because gm has two rev limiters...on autos that is, the 4k n/p and the 6500rpm rev limit.

so imo theres no way that it could be....

You callin bs on ME??


Sorry for the delay in responses though. Just got back from my honeymoon.

[IsaacHayes]

Ignition Control Module. If it's not bolted down tight on that aluminum plate it's likely over heating. The plate acts like a heatsink. It will heat up quicker at higher RPM's. Try bolting it down. If that doesn't help then swap out with your GP's ICM and see if the problem goes away. If so then you found it.

[85_305]

Well this is on my '93 Sunbird.. 3.1 and 5sd.. but can it still be the same problem?

[IsaacHayes]

The GP and the SB both use the same ICM module. I said to swap them over, swap the coils and ICM (the thing the coils plug into) between the two cars. Then if the SB drives fine, you know that it was a bad ICM which is now on the GP.

Beats buying a new part when you have the same part you can swap and test out first to see if that really is the problem.

[85_305]

Ahhhh gotcha. Only problem is the GP is sold lol. But I will first try to bolt the coilpack back down to the block, then take a gander at the ICM..
You think there is a really good chance it's one of those two?

[pontiac3100]

sorry i did'nt mean you said a mechanic plus i've never heard of this feature.

there's way to check the coilpack primary and secondaries...but you have to have a ohm meter on hand and the coil has to be cold.

the icm you could take to a local autozone...and they should have a machine to test it.

issachayes has a point i was told the same thing and that somewhat helped then i also made a "better" ground for the coils/icm.

it seems like a load thing beucase you said there wern't no missfire's at higher speeds when in 4th or 3rd.....

again i'm sorry....

[85_305]

sorry i did'nt mean you said a mechanic plus i've never heard of this feature.

there's way to check the coilpack primary and secondaries...but you have to have a ohm meter on hand and the coil has to be cold.

the icm you could take to a local autozone...and they should have a machine to test it.

issachayes has a point i was told the same thing and that somewhat helped then i also made a "better" ground for the coils/icm.

it seems like a load thing beucase you said there wern't no missfire's at higher speeds when in 4th or 3rd.....

again i'm sorry....

Oh it's cool.. i just thought you were saying I was making this whole thing up lol. But autozone will check the ICM? Hell I will just make their ass do it then lol.
I will take it to autozone, then BOLT DOWN my coilpack (lol) and see what happens.. but the mechanic did infact say that it's a load-based piece of electronic-"heaven".

[IsaacHayes]

Hmm if the coils aren't bolted to the ICM to hold the ICM to the plate that can be a problem. If the plate just isn't attached to the motor well then that shouldn't affect it's reliability.

When the ICM's go bad they start to miss fire at higher RPMs when they get hot. They are $$$ so finding a spare or cheap used one to throw on is better than dropping $$$ for a new one in case that isn't the problem.

However every time I've had a problem it turned out to be the CPS not the ICM. But usually my CPS gets worse and it will run crappy at all RPM when it acts up.

[pontiac3100]

don't mean to hi jack but what about the 24x sensor (behind the crank pully)

but back to your thread...now that you mention it i went through loads of icms....and i got one off of a 94 l82 and they had replaced it.

i had put it on...no high rpm "missfire".
then i put my old one on...then it happened again.

so i put the "new" one on.

also you have to take off the icm then take it in...

[85_305]

Hmm if the coils aren't bolted to the ICM to hold the ICM to the plate that can be a problem. If the plate just isn't attached to the motor well then that shouldn't affect it's reliability.

When the ICM's go bad they start to miss fire at higher RPMs when they get hot. They are $$$ so finding a spare or cheap used one to throw on is better than dropping $$$ for a new one in case that isn't the problem.

However every time I've had a problem it turned out to be the CPS not the ICM. But usually my CPS gets worse and it will run crappy at all RPM when it acts up.

Figured out the problem. My coilpack has been gradually loosening from the block. Heard a ticking noise under the hood last night, and was pissed thinking it MIGHT have been a lifter, but it COULD have been that coilpack. I pop the hood w/ it running, the pack is just dangling there, and one of the wires is sparking like crazy cuz the fan cut it open. I told some mechanics about it, and were amazed the car was still running from the coilpack not being grounded. That shits gonna be fixed tomorrow morning