Okay this thread is going to have a lot of information. I appreciate everyone who tries to help out!

My car:

AP1 motor, stock block, ported and polished head
Kraftwerks Supercharger
750cc injectors
Walbro 255 fuel pump
Kpro ECU
AEM UEGO Wideband
High Flow Cat


Problem:

The car is misfiring under load / boost. Car drives absolutely fine with no misfire in lower RPM (under 5k) or under low load. Once I step on the gas, car would start to boost and start from 5000rpm the car would start to hesitate and misfire, air fuel gauge would go pig rich. No Check Engine Light

The car was tuned by Mase and drives very very smoothly after the tune. Nothing has been changed ever since the tune. The problem started to happen after the 3rd session of track day. For the first 3 session, car drove beautifully. After the 3rd session, I filled up a full tank, Chevron 94. Drove back to the track, right off the bat it started to misfire.

When it first happened, the misfire was REALLY REALLY BAD. Every time when I hit around 5000rpm, the car would misfire and will not continue to rev up. It feels like a rev limiter. Air Fuel gauge goes pig rich when it happens. No Check Engine Light.

I was able to drive back home and it drove very smoothly as long as I was under 5000rpm and off boost.

I suspected it was a bad tank of gas. When it got down to about a quarter tank, I filled up again. As soon as I left the gas station, I was able to rev up to 9 again! BUT it is still misfiring in the middle of the rev range (5~7k rpm). Car feels like it is hesitating, and air fuel will go pig rich. No Check Engine Light.

I have now filled up twice ever since then, and car is still doing the same thing.


Here is a list of things we have checked:

No Check engine light
No Error code
No vacuum leak
No boost leak
Checked boost bypass valve
Switched Coil packs with another s2k
Put in brand new NGK BRE7k Plugs gapped at 0.025
Checked Map sensor, datalog shows it's reading correctly
Checked TPS sensor, datalog shows it's reading correctly
Put in new O2 sensor
Compression test: 240 240 240 240
Fuel pressure looks good
Oil level good
Coolant level good




So guys, any suggestions or ideas?

 

injector sticking open? check your plugs.

 

The plugs were replaced a week ago, had about a tank on them.

We took them out today and the tip is white.

What does that mean?

 

means your idle is probably lean. You would have to post some pictures to get any accurate assessments. Its hard to diagnose these things over the interwebs.

 

Happent to me twise, first time was one of the spark plugs burned and the 2nd time happent because of one of the injectors wire..

 

Injector wire, so your injector was not injecting fuel?

Wouldn't that cause problem all the time instead of just under load?

 

 

May need to get your injectors checked. They can flow test them for you and make sure they are opening and closing and sealing appropriately.

 

Datalog it and check your timing, make sure VTEC is engaging, Knock, fuel injector pulse width......

 

Injectors maybe?
Flaring the fuel lines, or any type of drilling, tapping etc can leave behind the smallest of objects, and can make their way through almost anything, i was able to knock out metal from my injectors after the original builders flared the fuel lines.