for the past 6 months i've been fightiing a mysterious and intermitant problem.

the car will run fine for weeks of normal driving, but after reving the motor up, it seems to start misfiring on cyl 5 and 7.

now this seems to be related to when i rev it...like a WOT blast or just running a lower gear up a little.

here is what i've done to remedy the problem..but to no avail:

plugs, wires, coils, cleaned coil connections, flushed the oil and used fuel injector cleaner.

i'm thinking that either the lifters are bad, or maybe the springs are weak. i think like this...the lifters are getting pumped up more than normal, not allowing the valves to close fully. from what i've been told this could be weakened springs or bad lifters.

i say "weakened" instead of broke because the problem goes away for weeks at a time...a mechanical break would be constant.

any input?

i plan to get a compression test i think, that may help narrow it down a bit more

 

My car has always had a loud valvetrain sinces day one, and has gotten even louder with my headers an cam, but I replaced the springs. I think it is something we all have to live with, that if the noise you are talking about is a loud ticking that comes and goes and gets louder at times?

 

oh no...i'm not talking noise...this is a full blown MISFIRE...ecm records several thousand misfires in some very short periods. the car will barely run

and scanning shows it on cyl 5 and 7