Just failed a smog test, Passed the last one about 3000 miles ago. The Jeep doesn't see much street duty. The motor is stock.
Since the last smog check:
Recent oil change
New 02 sensor
New TPS sensor (set closed position voltage at 0.85V)
New Cat
New Dynomax exhaust
4.89 gears
Seems like a lot of changes but not really.
I've checked functionality of the EGR and it is operating when I bump the throttle. My concern is the fact that since it's a positive backpressure EGR and I'm wondering if the combination of the free-er flowing exhaust and the low gears are affecting the backpressure. Gears? When he was on the rollers the car did get into overdrive so the RPMs were pretty low on the tests. This is moving less air through the motor so the backpressure is less. The EGR will not function correctly w/out backpressure in the exhaust. Low enough backpressure for the EGR to not function? I don't know. I wouldn't think so. My first thought is to retest and have them leave it in 1-2 so it doesn't go through the gears to keep the RPMs higher to help the EGR function. I've searched high and low for a vacuum leak and can't find anything.
I did notice that the measured oxygen levels were higher than they were the last time I smogged it and that is consistent with higher combustion chamber temps which lead to higher NOx. But I'm not getting any "lean exhaust" trouble code so it's probably within an acceptable range. I pulled off the EGR and cleaned it and checked it for functionality and it seems fine. Like I said earlier I did notice it moving when racing the engine. I wish there was an EGR position sensor on it so I could verify that it was open during teseting.
High NOx is from high combustion chamber temps. This is caused by vacuum leaks (lean mixtures) and/or an EGR that isn't functioning. I can't find a problem with either so I'm at a loss. Fuel pressure checked out fine by the way. Maybe it is just the combination of the gears/exhaust and I need to have them test in 1-2 on the transmission? Any other CA jeepers run into this? I'm sure aftermarket exhaust and low gears isn't unique on this forum. Help!!!! chasing my tail right now.:repair:
Since the last smog check:
Recent oil change
New 02 sensor
New TPS sensor (set closed position voltage at 0.85V)
New Cat
New Dynomax exhaust
4.89 gears
Seems like a lot of changes but not really.
I've checked functionality of the EGR and it is operating when I bump the throttle. My concern is the fact that since it's a positive backpressure EGR and I'm wondering if the combination of the free-er flowing exhaust and the low gears are affecting the backpressure. Gears? When he was on the rollers the car did get into overdrive so the RPMs were pretty low on the tests. This is moving less air through the motor so the backpressure is less. The EGR will not function correctly w/out backpressure in the exhaust. Low enough backpressure for the EGR to not function? I don't know. I wouldn't think so. My first thought is to retest and have them leave it in 1-2 so it doesn't go through the gears to keep the RPMs higher to help the EGR function. I've searched high and low for a vacuum leak and can't find anything.
I did notice that the measured oxygen levels were higher than they were the last time I smogged it and that is consistent with higher combustion chamber temps which lead to higher NOx. But I'm not getting any "lean exhaust" trouble code so it's probably within an acceptable range. I pulled off the EGR and cleaned it and checked it for functionality and it seems fine. Like I said earlier I did notice it moving when racing the engine. I wish there was an EGR position sensor on it so I could verify that it was open during teseting.
High NOx is from high combustion chamber temps. This is caused by vacuum leaks (lean mixtures) and/or an EGR that isn't functioning. I can't find a problem with either so I'm at a loss. Fuel pressure checked out fine by the way. Maybe it is just the combination of the gears/exhaust and I need to have them test in 1-2 on the transmission? Any other CA jeepers run into this? I'm sure aftermarket exhaust and low gears isn't unique on this forum. Help!!!! chasing my tail right now.:repair: