smogged OK- NOx better now
04-22-2011, 05:49 AM
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smogged OK- NOx better now
I failed NOx on my 1st attempt at Cali smog:
15 MPH HC=36 CO=0.21 NOx=987 (pass would be 689)
25 MPH HC=17 CO=0.10 NOx=727 (pass was 730 ...)
car is mostly stock with an Autothority chip and boost increase, still has the Porsche cat. It's been marginal on NOx for all 8 years that I've owned it. Car has always driven just fine. It hasn't been used much in the last year as my back was having a year-long hissy fit, so the fuel was rather stale. Smog guy suggested changing the plugs, possible O2 sensor issue, or exhaust leak, then cat. When I searched the net, I read that the 3 way cats without air injection dither the AFR from lean to rich so that the 1st section (for NOx) works on the rich phase (I think that was it) and the remaining sections work on the HC and CO by storing oxygen during the lean phase. A buddy of mine pointed out that O2 sensors can slow down with age. So it seemed to me possible that the O2 sensor might look OK to simple voltage tests, and yet be too slow for proper cat function. I did not check my sensor voltage-I'm pretty sure that it functioned to some degree, as the HC and CO were OK and the car plainly switched to closed loop operation soon after starting. But I changed the O2 sensor anyway. Actually I did a few other things too:
1. replaced O2 sensor
2. replaced plugs (they looked just fine though)
3. emptied the fuel tank, put in 2 gal of Chervron 91 oct. I didn't fill it up in case I had to play ethanol games if it failed again...
4. bumped the tire pressure to 50 psi. Supposedly NOx comes from high combustion pressure (load), so I figured anything that could reduce the load would help.
I drove the same 9 mile loop to warm up prior to the smog stop. Results now:
15 MPH HC 70 (YES IT WENT UP) CO 0.20 NOx 397 (yippee!)
25 MPH HC 20 (also up) CO 0.10 NOx 422
I think that it's pretty clear that the O2 sensor was the trick- the higher HC suggests that it may have been on the rich phase too little of the time with the old sensor. Of course you probably have to have the cat for this to be effective.
hope this helps someone
Gary
15 MPH HC=36 CO=0.21 NOx=987 (pass would be 689)
25 MPH HC=17 CO=0.10 NOx=727 (pass was 730 ...)
car is mostly stock with an Autothority chip and boost increase, still has the Porsche cat. It's been marginal on NOx for all 8 years that I've owned it. Car has always driven just fine. It hasn't been used much in the last year as my back was having a year-long hissy fit, so the fuel was rather stale. Smog guy suggested changing the plugs, possible O2 sensor issue, or exhaust leak, then cat. When I searched the net, I read that the 3 way cats without air injection dither the AFR from lean to rich so that the 1st section (for NOx) works on the rich phase (I think that was it) and the remaining sections work on the HC and CO by storing oxygen during the lean phase. A buddy of mine pointed out that O2 sensors can slow down with age. So it seemed to me possible that the O2 sensor might look OK to simple voltage tests, and yet be too slow for proper cat function. I did not check my sensor voltage-I'm pretty sure that it functioned to some degree, as the HC and CO were OK and the car plainly switched to closed loop operation soon after starting. But I changed the O2 sensor anyway. Actually I did a few other things too:
1. replaced O2 sensor
2. replaced plugs (they looked just fine though)
3. emptied the fuel tank, put in 2 gal of Chervron 91 oct. I didn't fill it up in case I had to play ethanol games if it failed again...
4. bumped the tire pressure to 50 psi. Supposedly NOx comes from high combustion pressure (load), so I figured anything that could reduce the load would help.
I drove the same 9 mile loop to warm up prior to the smog stop. Results now:
15 MPH HC 70 (YES IT WENT UP) CO 0.20 NOx 397 (yippee!)
25 MPH HC 20 (also up) CO 0.10 NOx 422
I think that it's pretty clear that the O2 sensor was the trick- the higher HC suggests that it may have been on the rich phase too little of the time with the old sensor. Of course you probably have to have the cat for this to be effective.
hope this helps someone
Gary
