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Not uncommon Posted by Justin VanAbrahams [Email] (#32) [Profile/Gallery] (more from Justin VanAbrahams) on Sun, 1 Sep 2002 12:38:10 In Reply to: Re: Man! Typo City, Nigel, Sat, 31 Aug 2002 15:03:20 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Readings going up after you mess with the mixture is NOT uncommon. When the engine is running its best, NOx emissions will probably be outrageously high. Engines are most efficient and produce the best power when they're hot (assuming the intake is cold....) but this causes NOx emissions to rise. All Saabs since the beginning of time have been designed to run more lean and not rich - just ask any of the guys tuning their turbos. In perfect *running* shape, a Saab won't pass NOx tests without a good catalytic converter. Saabs run very clean in terms of all other tested output (often unbelievably so) but they really aren't good in this category.
The easiest thing to do is back off your timing. Setting it to 14 degrees BTDC is within spec (16 +/- 2 degrees, according to most emissions manuals) and will substantially reduce NOx output. The car will be a complete slug like this, but it really should help. Combine that with a couple cans of the aforementioned Top Engine Cleaner and you should fly right through... even the most well-maintained car probably has some nasties in the combustion chamber, and even small carbon deposits can have quite an influence on NOx output. That cleaner will get them out.
If you car still fails after this, see if the shop you go to has one of those cool infrared exhaust temperature probes. Have them verify the cat is at operating temperature, and that the exhaust is hotter after the cat than before. This will tell you if your converter is working - you may need a replacement. A cat *should*, in theory, last the life of the car, but few people are anal enough to keep the engine running perfectly all the time. Oil, gas, etc. in the exhaust can foul a cat pretty quickly.
-Justin
posted by 64.166.4...
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