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interesting misfire issue

C

CopperGTP

New member
I know there are tons of misfire threads, but never have I seen the issue I'm having now, and it's so weird that it's actually somewhat entertaining. What started off as a misfire under load (no CEL) has gotten gradually worse to where I finally did get a CEL (random multiple misfire), but part throttle driving is totally unaffected. So far I've inspected the plug wires for damage, and took the metal shields off the spark plug boots. I haven't bothered checking the coils or ICM yet, because I should be getting a set in the mail tomorrow, so I'm just gonna swap it all over. I still need to check the plugs as well. PO said they're new, and they're AC Delcos, but I don't know which "flavor" he used, or if he bothered gapping them. Here's where it gets weird.... driving to work today, all of a sudden I was getting alternator noise through my speakers, and the stereo wasn't even turned on. It would get pretty loud as I stepped on the throttle, then it would cut out and the car would drive as normal until it happened again. The misfire didn't really get any worse during the "noise storms" but if it did, I probably just could hear it over that noise. Maybe a rectifier in the alternator blew out? I wish it wasn't so cold out so I could check all these things properly without losing fingers to frostbite.
 


It was the coils. 2 originals reading just out of spec and one aftermarket reading perfect. Put used original ones on from a low mile 2005 Monte SS sc and the car runs great now. If I get the radio noise again, I’ll see if it’s possible to change just the condenser on the alternator. I’d hate to change the whole alternator because of a 50 cent part.
 
Strange! Glad you got it fixed though. It's amazing how these things can fail gradually and never show a cel.
 
I have seen a similar issue where no codes were tossed etc. It's interesting, but once in a while shotgunning a part on is the only way to find the solution.
 
Yeah, and when you get an opportunity to buy an original low miles set of coils and ICM for 40 bucks, you take it, lol. So now I still have a spare ICM too....bonus!
 
Wow. Misfires caught my attention. (I used to get sound through my speakers when passing a particular TV station transmitter).

Is it likely for ICMs to go bad? I've had an intermittent misfire for a long time and am still trying to solve it w/o remove-and-replace policy ($). ('05 GTP; have replaced plugs, wires, injectors, checked vacuum lines; have not replaced crank position sensor or ignition coils).

Pardon the deviation from your thread, but I have been wanting to replace the ICM but don't want to just throw "possible" parts at the problem anymore.
 


search ebay and keep an eye out for a good deal. Sometimes you can find stuff so cheap it doesn't make sense to not buy it. My whole ICM with all 3 coils was $40 shipped to my door.
 
I see. Some even sound trustworthy (I once tried this with one from a junkyard module - either it was incompatible or bad; I assumed the normally asiprated GP was not compatible since the car ran horrible). Do you know if it's the same ICM through all GP models? I'm seeing several part numbers (of which there MAY be backward compatibility but not the correct replacement for supercharged (GTP).
 


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