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Old 05-21-2003, 10:18 PM
unkl300d's Avatar
unkl300d unkl300d is offline
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Join Date: Jul 1999
Location: San Francisco, Ca
Posts: 2,275
Red face lazy oxygen sensor

My 300SE failed the California Smog test. (127K miles)

At 2500 RPM

Max AVG. My car fail #1 my car pass#2
HC(ppm) 140 20 287 26

CO % 1.00 0.10 6.26 0.02


HC ppm 120 20 405 20
CO % 1.0 0.1 4.48 0.01

Well, after the failure (rich fuel-mix) my mechanic took out his nice long screw driver and set it in the opening at the air cleaner housing top.
Adjusted something while his meter was connected (lambda???)

He observed that I had a lazy oxygen sensor and the reading was erratic. He made some compensation and sent me back to the test station. (another pop$) It passed.

Afterward I had him replace the oxygen sensor and he readjusted the car. Runs well and the idle became a bit more steady.

Thanks to these archives I educated myself to possible scenarios
as this transpired over 2 days.

So, I record my anecdote for others' research.


1979 300D 199 K miles
1995 C280 95 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles
1979 240D 140Kmiles (bought for parents) *SOLD.
1989 300SE 148 K miles *SOLD
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