My EGR valve has gone bad on my Camaro....hesitates a bit under light throttle and it wont hold a vacuum....so i unplugged the vacuum line from it..plugged off the vac line and the car runs perfect. The question is....how come I am not getting a SES light from disabling the EGR?!?! Drove the car on a 400 mile road trip and to my surprise i never got a SES? Does this seem weird to anybody?

 

The OBD-I diagnostic doesn't seem to be very sensitive to a non-functioning system. It's the same logic use in OBD-II: cycle the EGR valve and look for a small change in MAP (manifold absolute pressure). OBD-II seems to pick up the non-functioning valve maybe 90% of the time. OBD-I less than 50% of the time.


It's also possible you have not operated the car under the very specific conditions required to run the diagnostic. Since the PCM will be looking at the MAP sensor reading, it has to be very steady which requires stable throttle position for several seconds, under very specific RPM/MAP/TPS/MPH conditions.

 

Cool, thank for the quick reply Any harm in keeping the vac line unplugged to it until i can get a new one? Not really looking forward to replacing it with it being hard to get to :P

 

The EGR system isn't really the evil thing people think it is. It helps minimize detonation (knock) when lugging the engine, acts a little bit like "displacement on demand". Doesn't hurt perofrmance, since it doesn't operate at wide open throttle or above 3,500 RPM.

The problem with not operating the valve is that as long as there is no code setting, the PCM is still tweeking the ignition timing, and adjusting the fuel rate on the assumption that the system us still working. No serious damage, just not the ideal way to run the engine.

 

Could this also cause the car to run slightly rich?