blistovmhz
NAXJA Forum User
- Location
- Vancouver, BC
98 XJ - 4.0L.
Was getting 20-23MPG. Had to pull the exhaust for some work. Put it back together and now I'm running super rich and fuel economy dropped to 12-16MPG and slight power loss.
Upstream O2 sensor is working fine (should be better now that I welded up a small crack right before the upstream, but just south of the collector.
The downpipe wasn't welded to the cat - down, and was held together with an exhaust clamp. When I stuffed the connection back together, it of course didn't seal all that well.
So now I know my upstream O2 is working normally, and my downstream waveform looks ... normalish, and I'm not throwing a code, but running super rich, poor mileage, and decreased power.
So while this question has been posed a thousand times, everyone always has a different answer. I'm in the camp that believes that OBDII puters do in fact use the downstream O2, in combination with upstream O2, to set fuel trim. This would make sense in my case, as I know I've got an exhaust leak just before the cat, which is probably letting in O2, causing the downstream O2 to read very lean.
So, before I go tear everything apart again and start welding my pipes together (I'm not a good welder) does anyone know definitively if the downstream O2 has any influence on fuel trim in an OBDII equipped 98 4.0L?
Was getting 20-23MPG. Had to pull the exhaust for some work. Put it back together and now I'm running super rich and fuel economy dropped to 12-16MPG and slight power loss.
Upstream O2 sensor is working fine (should be better now that I welded up a small crack right before the upstream, but just south of the collector.
The downpipe wasn't welded to the cat - down, and was held together with an exhaust clamp. When I stuffed the connection back together, it of course didn't seal all that well.
So now I know my upstream O2 is working normally, and my downstream waveform looks ... normalish, and I'm not throwing a code, but running super rich, poor mileage, and decreased power.
So while this question has been posed a thousand times, everyone always has a different answer. I'm in the camp that believes that OBDII puters do in fact use the downstream O2, in combination with upstream O2, to set fuel trim. This would make sense in my case, as I know I've got an exhaust leak just before the cat, which is probably letting in O2, causing the downstream O2 to read very lean.
So, before I go tear everything apart again and start welding my pipes together (I'm not a good welder) does anyone know definitively if the downstream O2 has any influence on fuel trim in an OBDII equipped 98 4.0L?