My 99 Sonoma - 2.2L, 5-speed - just tanked on CA smog test. Failed the NOx measurement at 25 mph. Max is 527, I measured 876. Passed NOx at idle. HC measure 0.0 (pass), CO measured 0.01 (pass). Anybody got an idea of what I am looking at with this high NO measurement? Truck feels like its running fine. No "Check Engine" light ever. New AC platinum plugs a few months ago. This vehicle doesn't even HAVE an EGR valve, which would be my first suspect.
Any advice appreciated. Thanks....
when the NO is high it's because the engine is running to lean and hot and is breaking down the oxygen molicule which combines with nitrogin to make N2O. I'd have the garage do a diagnostic on the engine management system to see if any of the censors are out of range.they could be out, but not enough to trip the computer warning light.
Just in the interest of helping anybody who has this same problem, here's the GM fix so far. I took it to big GM dealer early yesterday a.m.. Sat and waited for emissions guy to get in. He took one look at previous test results and said, "Oh, you're running 89 octane, aren't you? (yes, I was) "Run it out, run a full tank of Chevron 93 through it, bring it back to me when its almost empty. I will test it while you wait and I guarantee it will pass." He never even looked at the truck or tested it. He told me, "I don't have to look at it. There's nothing wrong with your truck." He explained that -- since '99 and later 2.2 do NOT have an EGR system -- many are doomed to fail new, stricter CA NOx standards at slow speed IF you take the test on regular (89 octane) gas.
Well, so at least the EGR controversy is settled. It'll take a while to run a full tank of 93 octane through it. Then I'll take the test again.
Most interesting. Please post back with the results when retested.
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