: EGR stuck = retarded timing?

05-10-05, 02:52 AM
I read on some website if the EGR valve isn't functioning properly that the PCM will retard timing to some lower base value. Is this the case with the northstar? Anyone know?

05-10-05, 05:22 PM
Bueller? Bueller? Bueller? :(

05-10-05, 09:47 PM
When EGR is introduced into the engine the spark advance is advanced dramatically to improve the efficiency of the engine. Interestingly, running a LOT of EGR and a LOT of spark advance under part throttle and cruise conditions improves the fuel economy significantly.

So...if the PCM onboard diagnostics discovers that the EGR system is not working correctly for some reason (like the code 36 - EGR valve pintle position problem) it will retard the spark to the non-EGR value table so as to prevent detonation if the valve is stuck closed and no EGR is flowing.

If the EGR system is restricted and not flowing (even though the valve is working correctly) the spark would not be removed and the engine would spark knock badly...then the knock sensor would sense the detonation and retard the spark to a non-detonation limit to avoid potential engine damage and/or eliminate the annoying pinging noise.

So...the answer to your question is yes in varying degrees depending on the EGR failure.

05-11-05, 03:49 AM
Thanks for the info. I've had a stuck EGR since I got the car, tried cleaning several times and nothing. I'll get a loan from the parents and hit up GM parts direct for a new one after I try cleaning one more time.