I have been running a 65mm pulley, 30# injectors, 3.5 bar fpr, 260/268 cam, SNS stage 4 chip for about 8 years now. Always ran fine until recently. Now if there is any boost, even 3-5lbs before 4k rpm it completely leans out, my a/f gauge goes blank and there is zero power. Once it hits 4k there is no problem, runs great all the way to red line. Now if I am driving it hard and it stays over 4k there is no problem, but I can't do that all the time mostly cuz I live in WA and everyone here is in a contest to see how far under the limit they can go.
The voltage is fine, brand new alternator/regulator. 14.3v at alternator, 14.1 at battery. Anyone got an idea what else would cause this?
1) bad grounds
2) O2 sensor messed up - try unplugging it (with stage 4 30# @ 3.5 bar the car should run rich without the O2 sensor)
3) fuel supply is bad (check rail pressure - FPR, maybe plugged fuel filter)
4) check the vacuum/boost line to the ECU and possibly the one in the ECU - if the ECU thinks the boost is lower than actual it will not supply enough fuel.
running like crap might also be the dreaded crank keyway issue