s2killlin

Quick back story.. My 2001 has intake, header, test pipe and T1R dual exhaust (2.75 inch pipes) has been set up like that for a while. Recently I ditched the blingy exhaust since its now a dedicated track car and just go straight pipe (3 inch pipe) from the header.

Last weekend I went to the next event I was signed up for and on my first session after 2 warm up laps the car had a major loss in power (most noticeably in the top end), no vtec and bogged really bad, not allowing me to rev over 6k. Seemed like it went into limp mode. I went in the pits, pulled the codes and got 3 misfire codes (cyl 2, 3 and 4), a vtec solenoid code (p1259) and a crankshaft position sensor code (p0335). I pulled off the vtec solenoid and it was clean. I disconnected the battery and cleared the codes between sessions. Again it was fine for the warm up laps but then it threw the codes again once i started revving it out harder.

Nothing with the engine has changed since my last event except the exhaust. Could I be getting the codes due to the exhaust and a lack of back pressure? I pulled the spark plugs and they seem to be a little white but nothing major. Maybe its running lean/misfiring now from the exhaust causing the ECU to throw codes? The car is not tuned but before this wasn't an issue so again that makes me think its exhaust/running lean related?Or would is it more likely think its an issue with the crank sensor? I have doubts its the crank sensor because if it was the code would show up as soon as i started it or drove it. Is there something else im not thinking of? I have a baffled oil pan, its picking up oil so i dont think its oil related.

Thanks in advance for any help.