Why might a '99 Grand Prix GTP misfire intermittently?

Answer 1

Hey George==A lot of times it is the injectors. Put some injector cleaner in the tank. also try spraying the plug wires and coils with WD40 with the engine not running. GoodluckJoe

AnswerA common problem for forced iduction engines is a fluxuation in combustion chamber environment. This includes mixture ratio, the degree of atomization of the fuel in suspension, heat and pressure. The bottom line is... change your spark plugs. I highly recommend NGK Iridium, especially if you are running a smaller pulley on you supercharger. They are very expensive, but worth it. I actually tried Bosch platinum and lost performance. If you have access to an Autotap or another scan tool, you an see which cylinders are misfiring. If you get a check engine light, the codes will tell you as well as long as the misfire set the code. AnswerIf your acceleration is weak and sluggish at times I would also check the catalytic converter. It can cause the engine to spit out misfire codes if the vaccuum is not right and it has to rev the motor to high to make it shift. As far as the spark plugs I agree with the NGK Iridiums, my Grand Prix GT has a very noticeable difference in power.

I agree with both and ig none of them are the problem check the egr valve. Mine was doing the same thing and putting up the 1404 code which is a misfire code. Good luck hope it helps.