BDD

I would like to know why headers makes the engine run rich.

Gev

I've heard they make the car run lean.

blkZ28spt

I think they usually make you run rich, but no two cars are the same. I too would like to know this, am intslling my Jet-Hots within two weeks w/o tuning. I know why open headers run rich, but why with a full exhaust?

LS1 Brent

Why do you run rich with open headers? Does it have something to do with the oxygen sensors?

QuikSSilver

its actually kinda hard to explain...... headers make your car run lean( so the puter thinks) so it compensates by fattenin it up... (l-trims i think)
it all has to do with what the computer see from the sensors... check out the PCM section adn do some reading then you'll understand more.

blkZ28spt

You run rich with open headers, I think because the oxygen from the outside air gets onto the front O2 sensors. Because of this the computer beleives that there is a lot of oxygen getting through the engine w/o being used. It then adds more fuel to the mixture (rich) in order to try and use that air and get the AFR back where it thinks it should be. Obviously, with open headers and outside air on the O2's, it is never going to accomplish this and just ends up running GD RICH. I mean RICH!