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Old 01-22-2004, 08:03 PM
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Join Date: Jan 2003
Posts: 9
failed smog check...please help

Hi All,

Brought my 89 300CE in for a smog check today and came out with a failed result. Here are the result numbers...any advice will be appreciated. By the way, I'm in California.

At 15 MPH
HC(ppm) CO(%) NO(%)
Max=110 Max=0.71 Max=772
measure=113 measure=.048 measure=1263

At 25 MPH
HC(ppm) CO(%) NO(%)
Max=85 Max=0.59 Max=711
measure=90 measure=0.41 measure=896


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Old 01-22-2004, 08:58 PM
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Join Date: Mar 2003
Location: Southern California
Posts: 2,270
The 103s have been identified by the CARB as a "high emitter engine family", and most are near or slightly above the limit on HC, but you also have a NOx problem, so you need to test the EGR system for proper function. Also, what is the history of your O2 sensor?

Since 103s are typically on the ragged edge, especially on HC, you need to "manage" the test. First, go to a drivethrough place at a time when the line is short. Stay in the car and keep the engine at 2000-2500 revs until the tech is ready to drive it onto the rollers. This will help keep the converters warm. If the car idles too long the converters cool and lose efficiency.

An even better strategy is to go on a rainy day, and specifically ask them to run the "tire dry test". This means they will run the car on the rollers with no dyno load at about 30 MPH for about a minute, but this is enough to heat up the converter and drop your HC count by 10-20 PPM, which will put you under the limit.

BTW, the NOx measurement is in PPM, not percent. It would also helpful if you would post the percent CO2 and O2 results.


Last edited by Duke2.6; 01-22-2004 at 09:04 PM.
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Old 01-30-2004, 08:11 PM
Registered User
Join Date: Jan 2003
Posts: 9
sorry for the late reply Duke2.6

Sorry for the late reply Duke2.6. I was out of town.
I have passed the smog check today after a new catalytic converter. I have owned the car for five years and this is the most expensive part that I've spent, but its time (182,000 miles). Thanks for the input.

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