Misfiring at WOT and 4k+rpms

[onegeenewbie]

The car was running fine at wot 2 weeks ago when I raced it last, however on the last run, it started to misfire above 4k rpms, and it's been doing it ever since. I did a boost leak test, and everything was solid. It will also misfire under any amount of boost, I was running ~15psi that day, and now I'm back down to 9psi and it still does it. I just put on a fpr and had the plugs, wires, fuel filter and cap replaced a month ago, so I'm not quite sure what the problem could be. Any thoughts?

 

[Dream On]

Check the plug gap and maybe try some other wires if you have some laying around.

 

[onegeenewbie]

I finally got around to re-gapping the plugs. They were all .035-.040, so now they're at ~.029. Test drove the car, and same thing is happening. It's def not a boost leak; it'll hold a 100% throttle and all the boost i throw at it only until 5k, then it looses power and misfires/knocks/stutters... not good. any thoughts?

I don't have any spare wires, maybe I'll pick some up tomorrow morning...

 

[Dream On]

Do you have a logger?

 

[blcknspo0ln]

Start with the basics:

boost leak, compression test, verify base ignition timing, check spark plugs, wires, transistor (this was my problem last time), inj plug clips, fuel pump, intake, MAF plug, ECU etc.

 

[onegeenewbie]

Do you have a logger?

Yes, I have a data logger and a SAFCII

EDIT:

It almost seems like an electrical issue with the ecu. I tried resetting the ecu, and it misfired less. Hopefully when I replace it with my eprom/keydiver setup, this will go away.

 

[taylorspl]

Pop off the valve cover and check the lifters. They can come out on a rare occasion or collapse and cause stutter in the higher rpm because of high cylinder pressure. Just something to check out since it won't cost any money.

 

[JayRolla]

I had these same problems lately. Turned out to be a burnt valve in the #4 cylinder. I would do a compression check to be safe.

 

[Siral3x]

-had the same problem on my 1g..it was the MPI relay..
Yep, do a compresion test before anything....and go from there.