Why does reduction in exhaust back pressure cause idle speed problems and engine stalls?

 

The short of it is that the engine is tuned for a certain configuration and any change to that configuration may require alterations to the ECU programming.

 

The good news is that someone, as Todd Knighton of Protomotive, can alleviate those symptoms while maintaining the engine diagnostics of the Motronics ignition.

Noah

 

zimpwh,
What exhaust modifications have you done ? It would take something pretty dramatic to give the side effects you describe !
Maybe you forgot to reconnect the O2 sensor ?

Geoff

 

Actually I have a Fabspeed System(dual rear tips)...headers to tips sans heater. I had my car in the shop last week for a Clewett Serpintine belt install. During the process the exhaust was removed and reinstalled for the engine partial drop. The drive home was smooth...nice idle, no stalls. When I went for a drive yesterday I noticed it was much, much louder and stalled/lugged as the revs fell below 3000 rpm. I raised the rear and found that the pipe between the headers and the muffler just behind the O2 sensor had come loose and separated...this I will have reattached today. I assumed that this lowered the backpressure significantly and caused the problems I have mentioned. I just wish to understand the process a bit better in theory.

 

OK,
It sounds like you had an exhaust leak before the O2 sensor ?
That means the O2 sensor signal, especially at idle/low speed , was not good and so the DME will get confused - stalling/poor idle etc.
It will have nothing to do with back pressure !

All the best

Geoff

 

Thanks Geoff. The leak was actually just distal to the O2 sensor...very close though.

 

PM sent.


Andreas