That's all easily verifiable by checking the O2 crosscounts:
Also the block learn and integrator.
My feeling is: Your header gaskets aren't sealing at the head flange correctly. (Ad do most headers, especially if they have a bead of weld at the pipe, to seal at the gasket. causing a vortec, and drawing in air to cause a lean signal at the O2 Sensor.
Now how the hell is that for a theory?
I've seen it, and fixed a few.
If that is in fact the problem, here's the fix! remove the headers, get a good bodyman with a flat (Sharp) metal body file. Have him screw it to a piece of 2X4 board.Have him screw it on the edge of the board, and start filing from one end to the other. If he didn't check it with a good straight edge first, you'll see all the low spots miraculously not get touched by the file.
Ten about an hour and a half after, the first header will be done!
Voila, no more poor fuel economy and shitty performance.
I hope this helps?
Refinish King
From: "Mad Dog" Subject: Re: Headers and the DAMN check engine lite Date: Tuesday, June 29, 2004 11:05 AM
the heated sensor will help the ECU while running in closed loop..........but installing the hedders forced the mixture over too the lean side because of the increased scavenging. the higher combustion chamber temperature may be causing some preignition which the knock sensor is hearing and then the ECU turns the light on because it's unable to compensate for the lean condition by going to full rich mode while retarding the timing. (holy crap, what a theory........huh) i don't know brother, maybe you knocked a wire somewhere that's pissing off the ECU. you could try changing the PROM chip in favor of a performance version, this would give you a fuel curve that takes advantage of the increased scavenging offered by the hedders. your guess is as good as mine friend.