Alpine951

I have trying to hunt down a lean lumpy afr at idle and cruising for a year. It happened after a WOT run on the highway. I have pressure checked, smoke tested , replaced certain parts thinking there is an intake or vacuum leak but have not had any luck finding one. I was trolling around on here searching and saw a post indicating lean running could be from an exhaust leak. Is this true and from what part of the exhaust might cause this? I gotta think this would be headers, crossover maybe.

Tom_DB1

I had a leak that caused my catalytic convertor to oxygen saturate so I would fail smog NOx with exceptionally high reading. The car ran perfect. A Gold Seal Smog mechanic here in Ca. stripped 1 of the bolts at the base of the down pipe but put it on so it looked ok. It passed smog that time but the next smog check the NOX were out of site. There was no exhaust leak sound or smell. My Porsche mechanic recommended a new cat which we did but did not solve the issue. It turned out to be the O ring at the base of the down pipe would allow air to be sucked into the exhaust at anything above an idle which stopped the cat from working. Plugged the leak smog passed great. I was surprised that even though there is pressure inside the pipe, the moving gasses could still suck in air from the outside.


Tom
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