My 1990 16v 740 just failed local, (OHIO) emissions.

NO's were at 1770 parts per million, limit is 1330 ppm.

I had just run the engine at high RPM for about 15 minutes on highway and had filled up with 93 octane the day before on an empty tank.

I was told that this failure is usually caused by hot running engine?

Maybe I should have left out the high speed run?

Any suggestions as to how to reduce NOs? Or what failed parts I might need.

I have less then a year on amm. Haven't cleaned the flame trap lately though.


thanks,
jc
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1985 740gle na, 1990 740gle 16 valve

Was that an idle test or a dyno test? If it was at idle, then suspect a lean mixture causing a high temp burn. If it was on a dyno, then check coolant temp, EGR if equipped, and AMM. Higher octane fuel burns longer and may burn hotter, use 87 next test unless the engine needs more because of pinging.

BTW; your high speed run had no effect on the test unless the probe was in the tailpipe at the time. Also, if it was a dyno test, the result means 1770 parts per MILE, not million.

I just went through this a couple of months ago. Turned out I had a very small leak in the intake hose between AMM and the throttle body. A well-warmed engine as you did is usually a good thing to do. If the engine is indeed too hot – find out why. Does your model have an EGR valve? If it does, be sure it is clean. Also check FAQ for more NOx info.
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Richard Montgomery 83-244GL ; '90-780t; '92-940; '80-242DL

http://www.brickboard.com/RWD/index.htm?id=754888
read this thread, good luck, chuck.