Addicted To Boost Posted February 3, 2011 Report Posted February 3, 2011 (edited) My car (88 Grand Prix SE, 2.8 5-speed manual) hasn't been running the greatest... When the engine is cold, it runs like complete ass. At anything under 2,000 RPM, it bucks like crazy and sputters... when cold, cruising in 4th gear at 32 MPH at ~1,400 RPM, it runs awful and my DIC says I'm getting about 8 MPG. Prior to this, in this exact same driving scenario, the car ran perfectly fine and the DIC indicated mileage in the mid 30s, if not better. If I accelerate at like half throttle and shift around 3k, its somewhat better. The symptoms seem to subside once the car is fully warmed up... but still seems to run rougher than it did during low RPM city driving. The car runs totally fine if you go WOT and grab gears at redline. What could I be dealing with here? Car has a full tank of gas, new AC Delco plugs and wires with like 3,000 miles of use on them... the coils are all good. I'm also getting 22 MPG with ALL highway driving... I know its been insanely cold lately, but that seems kinda ridiculous. Any ideas? Edited February 3, 2011 by Addicted To Boost Quote
Addicted To Boost Posted February 3, 2011 Author Report Posted February 3, 2011 And symptoms of a (failing) ICM are? Quote
AL Posted February 3, 2011 Report Posted February 3, 2011 Re read your first post... Lol but really a failed icm usually causes low rpm issues and spark issues... On my 91 is set the ses light but most of the time it won't... On my buddies Lumina it misfired like crazy due to the failed icm Quote
Addicted To Boost Posted February 3, 2011 Author Report Posted February 3, 2011 Interesting... I would have just expected to have these symptoms when hot, because that's when electrical components usually fail.... just seems weird that its doing it at cold temps. Quote
AL Posted February 3, 2011 Report Posted February 3, 2011 I have seen it do it cold and/or warm... Try replacing it and see what happens Quote
Night Fury Posted February 3, 2011 Report Posted February 3, 2011 http://www.youtube.com/user/BuckFiftyCutty#p/a/u/1/UT-jksTPZ8g Quote
Addicted To Boost Posted February 3, 2011 Author Report Posted February 3, 2011 Sigh... need to wait until its not -30* outside lol. I'll give it a shot. Any possibility this could be related to bad injectors? Quote
Addicted To Boost Posted February 3, 2011 Author Report Posted February 3, 2011 http://www.youtube.com/user/BuckFiftyCutty#p/a/u/1/UT-jksTPZ8g That's what it's doing... I wasn't watching the tach, but it's definitely bucking hard like that. Quote
Night Fury Posted February 3, 2011 Report Posted February 3, 2011 That's what it's doing... I wasn't watching the tach, but it's definitely bucking hard like that. That's what my 91 was doing with a bad ICM Quote
jman093 Posted February 3, 2011 Report Posted February 3, 2011 Could also maybe be a bad coolant temp sensor? If it's not accurate it often won't be noticeable until its ass cold outside. It would also explain why WOT runs are fine. A scanner would help you out. Quote
virtuetovice Posted February 3, 2011 Report Posted February 3, 2011 If nothing else, it could be a bad ass vacuum leak. My 2.8 did some uber-weird shit when it had a bad vacuum leak and the fuel economy was HORRID. Quote
slick Posted February 3, 2011 Report Posted February 3, 2011 Coolant temp sensor, vacuum leak, failed o2 sensor, could be a number of things. Quote
GOT2B GM Posted February 4, 2011 Report Posted February 4, 2011 Bad MAF sensor. Could be converted to speed density. My old 87 Z24 5 spd used to buck and stutter like a bastard when it was cold, and run like gold when warm. Had a new ICM, coils, plugs etc, never got around to changing the MAF but I heard they aren't the most reliable in the 87/88 2.8's Quote
slick Posted February 4, 2011 Report Posted February 4, 2011 Man... I always forget that the first year or two used MAF. Quote
Addicted To Boost Posted February 5, 2011 Author Report Posted February 5, 2011 Bad MAF sensor. Could be converted to speed density. My old 87 Z24 5 spd used to buck and stutter like a bastard when it was cold, and run like gold when warm. Had a new ICM, coils, plugs etc, never got around to changing the MAF but I heard they aren't the most reliable in the 87/88 2.8's IIRC, GM recalled all the 88s and converted them to speed density and reprogrammed the memcal... correct me if I'm wrong. Quote
Addicted To Boost Posted February 6, 2011 Author Report Posted February 6, 2011 (edited) There is a sticker on the driver's side strut tower that says it was "converted to speed density and the ecm was remapped". I replaced the ICM with a brand new one today and it still runs like shit. What else can it be? There is no check engine light. All vacuum lines are intact with no leaks, my HVAC vents and cruise all work correctly.... though it won't hold its speed on hills... maybe a bad cruise control module. Edited February 6, 2011 by Addicted To Boost Quote
tornado_735 Posted February 7, 2011 Report Posted February 7, 2011 Perhaps an O2? Bad ones wouldn't necessarily throw a code. Quote
Addicted To Boost Posted February 8, 2011 Author Report Posted February 8, 2011 Its running absolutely awful now... I don't know how much longer I'll even be able to drive it. New o2 from RockAuto is on the way... Quote
Garrett Powered Posted February 8, 2011 Report Posted February 8, 2011 did you already do plugs and wires? sorry if i missed that. Quote
Garrett Powered Posted February 8, 2011 Report Posted February 8, 2011 never mind. but did a ceramic crack or wire end break off maybe? Quote
Addicted To Boost Posted February 9, 2011 Author Report Posted February 9, 2011 I replaced the plugs and wires on it in December Quote
Addicted To Boost Posted February 13, 2011 Author Report Posted February 13, 2011 Since it was a balmy 34* outside today, I pulled off my intake plenum and checked out my injectors... Pulled the rail up and kept the injectors connected and primed the pump... no leakage. I ohmed out all my injectors and 4 injectors were right at 12.1 ohms... one was at 13.2 ohms, and one other injector was at 10.0 ohms.... So it looks like I have two bad injectors! Gotta wait until sometime this week to get a couple from the jy... then I'll pop in the new O2 sensor as well. Quote
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