Exhaust Troubles

[SidewaysAndHighways]

I have a 90 KA24E on which I have just installed a custom 2.5" exhaust from the header back removing the cat and putting a JCW Carbon Fiber Exhaust on. Everything runs great but the check engine light is intermittently on and off. ON more than off. Is the backpressure causing an issue with a sensor or do I need to reset the light? If so, how?

[naed240sx]

Why would backpressure be an issue? That is a perfectly acceptable size of piping to go with. Are you sure the two things are even related?

[InsanityInc]

Actually, yes. If your code is the EGR system, it's probably that you don't have enough backpressure to normally actuate the EGR BPT (backpressure transducer). In order for it to work, you can bypass the BPT by just running the vac line straight to the EGR valve. As long as your canister control/EGR solenoid is working properly, bypassing the BPT won't cause any issues.

[slipnfall]

Won't this cause the EGR to remain open at all times though?

[InsanityInc]

No. The EGR is primarily controlled by the EGR and canister control solenoid valve which is actuated at 2000rpm to open the EGR valve. The BPT is a secondary measure to only open the EGR at certain backpressure levels. For what reason, I don't know.

[SidewaysAndHighways]

OK, so I bypassed the BPT and the engine light went out, but now between 2k and 3k rpms if I hold the throttle at a speed holding level, the engine doesn't run as smooth. It is fine under accelleration and decelleration though. Would it be bad to just leave it the way it was before or is there a way to make it run smoother with the bypass? Thanks for the info before though.