2005 Grand Prix GTP intermittent acceleration sluggishness misfire

[roman1978]

I have this car for few months now and i have replaced catalytic converter o2 censor plugs wires pcv and still getting a misfire. Its intermittent. happens ever few times you start the car. Any suggestions what it can be the last time i scanned it showed cylinder # 3 misfire. When you accelerate the car feels sluggish and then at around 2500 rpm the supercharger kicks in and I know it should not do that under normal acceleration. Other times its just normal. So I know something is wrong. Can anyone suggest what else can it be.

[rickisrad]

I too have a misfire on cylinders 3 and 4. I replaced all the forementioned parts and it is still there. I think the next thing for us to check would be the coils and compression in those cylinders. Possible injectors??? I am going to check those this weekend. I will let you know what I find on mine. Does anyone know how to properly check the input and output of the coils?????

[roman1978]

does your misfire all the time or sometime mine was fine all day yesterday and today it stated doing it again. Is your check engine ligth on?

[rickisrad]

No check engine light on. mine is pretty much all the time. not major misses but noticeable. if yours is intermittent try using a spray bottle with water and lightly spray the coil, wires, and some of the electrical. look for a change of idle or bog, if it does you have a open wire or crack. Another thing to do is use carb cleaner and spray all vacuum lines and conections, around the intake and listen for the same thing. that is the easiest way to look for a vacuum leak. just spray one thing at a time.

[jml755]

Try swapping the coils/plug wires around. See if the misfire moves. My rough engine performance were misfires caused by injectors between 96k & 100k. Did #5 at 96k. #3 went bad at 100k and then decided to do the rest while I had things apart. Not real hard to replace. I've got a slightly rough engine at higher speeds now (with 134k on it), a little more pronounced under boost/acceleration, but no SES lite. Won't worry unless it gets worse. Doesn't seem to affect mpg. could be vacuum leak.

[rickisrad]

I checked the coil packs and all were fine. i used this method http://www.youtube.com/watch?v=eNx9YDodgE0 . i rechecked the plugs and they looked great, i tested the new delco wires and they tested fine. plenty of fuel pressure. i tested the compression of the front 3 cylinders and all were at 150 psi which is very good. So I am convinced that it is the injectors. I will buy some through zzp, and upgrade to a better set.

[tmwr2006]

I have had a similar issue with my car. Have you put an air intake in by any chance?

I found that 2 plastic retainers were broken off of a plug on my ECM which is directly below your air filter. This loose connection was causing my fuel injector in cylinder in 3 to stay open and that was causing missfire due to not being able to burn off the excess fuel.

I used some di-electric grease and zip-tied the connectors down and it has been fine ever since. Hope it helps.

[00_GTP Brewer]

My 2000 does the same thing, strange that it is also cylinder #3. I changed plugs (the plug in #3 burns up every couple of months) and wires, also swapped coils and cleaned injectors. Does anyone have better guesses?