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several weeks ago I posted:
I have a 940 non turbo with about 210,000 miles (with EGR and pulse air). In my recent smog, the NO value went over 2000 for both low and high speed tests. Needless to say I failed. I have been trying to figure out what is wrong. The first thing I did was check the EGR system. It passes all the factory manual tests and functional tests. No codes are set. My milleage is fine (I still get 30 mph on the highway). I loose oil, but that is through the rear main seal. My compression is 200 psi plus or minus 10 psi on all cylinders (it was about 195 two years ago). This was a dry pressure (no oil added to cylinders). I did a leak off test. All cylinders are about 18% with the leakage through the intake valves (I can easily hear and just feel the air flow from the opening of the intake manifold). The valves are noisy, but they always have been. The head was rebuild at about 140,000 miles. The recent smog readings were:
at 15 mph: 02=0.3, CO2=14.5; HC=80; CO=0.44; NO=2256
at 25 mph: O2=0.2; CO2=14.7; HC=38; CO=0.36; NO=1816
Two years (~165,000 mi)ago the readings were
at 15 mph: O2=0.1; CO2=15.3; HC=28; CO=0.03; NO=341
at 25 mph: O2=0.0; CO2=15.3; HC=10; CO=0.02; No=437
The readers suggestions where that the 02 sensor was partially bad or that the cat convertor was bad. I took your advise and replaced both of them. I passed smog. the readings were:
at 15 mph: 02=0.1, CO2=14.9; HC=55; CO=0.13; NO=621
at 25 mph: O2=0.0; CO2=14.9; HC=20; CO=0.03; NO=90
as you can see, things are much improved. My question is: is the high NO at low idle caused by air leakage through the valves (see the leak off test data) or is there another cause?
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