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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / May 2005How I solved my (slightly) high NOx emissions problem
I have a 1996 Mazda Protiege that was BARELY failing my state's emissions test (reading 3.12; my state allows 3.00 max). The car had been recently tuned up, so I knew the usual culprits (EGR valve, timing, etc) were not the problem. I figured I could pass the test if I could get my engine temp up a few degrees. But the thermostat I have is already the hottest available for my vehicle (which also happens to be the OEM spec - no aftermarket thermostats are hotter than the OEM thermostat). So I went home and "installed" a piece of cardboard that covered half of the radiator (placed in the center) and went back to take the test again. I wasn't sure if it was gonna work - the temp gauge was reading only slightly higher than it normally is (about 1/8 of the gauge sweep, but the gauge not marked in degrees, so I don't know exactly how much that is). However, the car EASILY passed with an NOx reading of 2.15 (almost a FULL POINT lower)! I cannot say for sure EXACTLY how much of this improvement could be attributed to the cardboard alone - I re-took the test at the same location but in a different bay (with different techs), so maybe there is an equipment sensitivity or operator difference (maybe I could have passed the test the first time if I had been in the other lane). But I think the temp certinally had SOME role in lowering the NOx reading, because it's hard to imagine there could be THAT much difference between one lane and another! Cheers! ... >However, the car EASILY passed with an NOx reading of 2.15 (almost a >FULL POINT lower)! plenty of clean air garages will fail you the first time cause they don't make any money on the test. then they get some easy repair money and pass you the second. they're careful not to milk you too much. or maybe the second time they tested as soon as you drove up. and the first time they let it cool down. ...thehick In Oregon, the inspection stations are owned and run by the state government (they are an extension of DMV). You don't pay if your car fails a test. >In Oregon, the inspection stations are owned and run by the state >government (they are an extension of DMV). You don't pay if your car >fails a test. OK. It's different here in Ontario. VERY different. ...thehick > I have a 1996 Mazda Protiege that was BARELY failing my state's > emissions test (reading 3.12; my state allows 3.00 max). The car had [quoted text clipped - 7 lines] > take the test again. I cannot say for sure EXACTLY how much of this > improvement could be attributed to the cardboard alone Exactly none. Higher engine temps reduce CO and HC...and INCREASE NOx! Lower engine temps increase CO and HC...and REDUCE NOx. > I have a 1996 Mazda Protiege that was BARELY failing my state's > emissions test (reading 3.12; my state allows 3.00 max). The car had [quoted text clipped - 28 lines] > > Cheers! Unlikely. The hotter the exhaust the more NOx will be produced. You raised the NOx output of your car by raising it's temperature. Read up on combustion chemistry. Wow, really? I'll admit to ignorance, but my experiences contradict this. If this is true, then my NOx was actually HIGHER, so the entire difference in readings was which lane I was in. The difference is surely far more than the equipment tolerance - maybe one lane had a faulty piece of equipment. > Wow, really? I'll admit to ignorance, but my experiences contradict > this. If this is true, then my NOx was actually HIGHER, so the entire > difference in readings was which lane I was in. The difference is > surely far more than the equipment tolerance - maybe one lane had a > faulty piece of equipment. Yes. Hard to say. It's possible the air/fuel mix was lean the first time. Possible EGR stuck partially open, vac leak, rich biased O2 sensor, etc. We would have to see the rest of the numbers to say more. In article <1115945728.441310.220370@g47g2000cwa.googlegroups.com>, > Wow, really? I'll admit to ignorance, but my experiences contradict > this. If this is true, then my NOx was actually HIGHER, so the entire > difference in readings was which lane I was in. The difference is > surely far more than the equipment tolerance - maybe one lane had a > faulty piece of equipment. I'd suggest that what ever thermal control controls your EGR valve wasn't allowing it to open due to insufficient coolant temperature, blocking off the radiator as you did raised the coolant temperature enough so that the EGR became functional. Other than that, there is absolutely no reason why higher engine temperature would equal lower NOx. >I have a 1996 Mazda Protiege that was BARELY failing my state's >emissions test (reading 3.12; my state allows 3.00 max). The car had [quoted text clipped - 28 lines] > >Cheers! All else being equal, raising the engine operating temperature should have increased the NOx and reduced the HC & CO. NOx is produced by high combustion temperatures. One of the big problems with an emission inspection is shutting the engine down just prior to the test which allows the converter to cool. The test is then conducted with the converter at reduced efficiency. If possible, the converter can be warmed by bringing the engine up around 2k RPM for a couple of minutes immediately prior to starting the test. Having seen this done numerous times by the local inspectors, it can have have a considerable effect on emissions. Most of the stations here do this routinely because they do not get paid for retest within 10 days. A 10-15 miles drive on the freeway or a fresh oil change just before a test can help reduce HC on those vehicles that are mostly driven in town. I suspect this is because of the fuel contamination of the oil. Good luck Lugnut the difference could be due to the engine temp when tested. here they recommend driving the car for 20 min prior to bringing it in for the test to make sure the engine is fully warmed up. my '89 Festiva barely passed the test. I took off the EGR valve, cleaned, and lubricated it. The next test was 90% lower NOx. I wrote up a description of cleaning the EGR valve and put it on my website under www.ncf.ca/~ag384/Cars.htm . -- ------------------------------------------------------------------------------ William R Watt National Capital FreeNet Ottawa's free community network homepage: www.ncf.ca/~ag384/top.htm warning: non-FreeNet email must have "notspam" in subject or it's returned |
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