Maybe I've been looking at this in the wrong direction. I've been chasing a stumble and trying to fix that, but what if.....


What could possibly be the cause for a car to just suddenly start running rich out of nowhere??? I've been trying to focus on the stumble, when in fact I think that it may be stemmed from the overly rich condition.

The car ran fine the first time on the dyno. Opti seal blew out, so that was replaced along with the crank seal which was initially thought to be the culprit. After that, the next time the car was run the rich problem and stumble/hesitation was there.

Any thoughts anyone??

 

Ok, heres my take on it....

my car used to stumble real bad in 4th(a4) when I would lay into the gas at about 1200 to 2000 rpm, every time it hit 2k it would drive like normal.....im sure thats what yours is doing. Well for a long *** time I never could figure it out, then like a week ago, I finally got a ses light and went to get it scanned and sure enough it said oxygen sensor failure(2). Then when I got home, (i got the 2otl exhaust) above the exhaust it was covered in...richness.....ive yet to change the sensor, gettin it changed this weekend, but I unplugged it and it hardly stubles at all. I'd say a lot of the stumbling people get is attributed to a rich condition.....when my car would stuble it would actually sound like its getting loaded up with fuel or something....oh well, hope that solves your prob.....heres a pic right after it threw the code....

I wiped my finger across each side of the bumper to show the difference

 

Well, I've got two new O2 sensors because my old ones are pretty black now....but........

It's definitely rich. The second time we went to the dyno, it tipped in at 10.7 at 2500 and leaned to 13.0 at 6000. The first time on the dyno it was 13.0 to 4200 rpm, then gradually leaned to 14.0 at about 5800 when we shut it down.

That, and my problem is present in open loop as well as closed loop.