cars with checking engine light

[ILikeMy240sx]

When your check engine light comes on... does it automatically retard the timing and run rich?

[hybrid_flyer]

depends on what year, if its 96 or later, then the car is in open loop because the emissions are greater than 1.5 the standard. Meaning the computer is using fixed values for injector pulse and spark timing, meaning it has no control of fuel management. if its 95 or older then it can be for a lot of different things.

[ILikeMy240sx]

I have a 96...

So when the check engine light is on the ECU doesnt care about the A/F ratio or anything like that? It just runs on a fixed value?How much performance is lost when the engine light is on?

[hybrid_flyer]

well it goes into open loop like when the car is warming up, its all for the oxygen sensor. If the problem is bad enough the MIL (check engine) light will flash, which is a warning of immediate cat damage danger. You will run rich, and lose some fuel economy, but the real danger is losing both the cat and your oxygen sensors