I have a 1983 380sec that failed california smog as a gross polluter. The car is off the charts in terms of HC and CO (about 10 times max allowable readings), and Nox at nearly zero. The car has also has slight miss at idle. The car starts just fine when cold or warm and does run good, but feels like it is lacking some power. Things I've check so far is control fuel pressure, which is at about 3.4 bar. With the car fully warm, the on/off ratio is fluctuating between 6-7% which indicates something is wrong, since it should be around 45-50%. I've exchange the oxygen sensor for a new one, and tried to adjusting the CO mixture, but the duty cycle reading does not change. I know for a fact that the vacuum advance on the distributor is not working, but I don't think it will affect the reading that much. What are some of the things I should check that can cause a car to run rich all the time. I'm going to check to make sure the cold start valve is not stuck open all the time tomorrow. Just need more ideas on what to check. Thanks for any help in advance.

i had the some results on my 16 valve, it turned out to be bad pre cats, i dont know if that applied to you, but i would have them replaced.

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Current
2006 E320 CDI, 57K bought at 67K "Liesl"
1986 190E 2.3-16, 198K bought at 56K "Brigitta"
1987 300TD (Chuggin Along), 292K "Friedrich"
1995 E320 Wagon, 200K "Louisa"

Past
1987 300SDL, (sold) 125K, bought for 1$ "Kurt"

Isn't fuel pressure supposed to be up around 5 bar - at least to the accumulator? On the K-jetronic, the fuel injectors are supposed to close completely at 3.3 bar (depending on which bosch book you read).

Correct me if I'm wrong (which I very well may be), but duty cycle on the K-jetronic system is measure in time off, not time on (of your injectors), which means your system is only not delivering fuel 6-7% of the time, which would make sense if your fuel pressure is overly low (and cause a very rich reading) or you have "extra" fuel making it's way into your system. Too low of a duty cycle, and the injectors don't have time to seat; they basically are in an on or partial-on state all of the time.

You could also check your cold start valve - it could be leaking or the time switch may have it constantly operating; that would definately cause an overly rich condition, however I think your duty cycle would be higher.

Oh, and vacuum advance not working will affect smog tests and driveability.

If you go to pdfdatabase.com, you can find plenty of bosch e-books on all of the different injection systems.

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A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.

Try this.

Disconnect the and ground the wire from the temperature sensor on the oil filter housing. That should put the system at a 60/40 or 70/30 duty cycle. Let the car warm up fully

Then test the voltage between your new oxygen sensor and ground. See if you can adjust the mixture to get a .45 volt reading. Then reconnect the temp sensor wire and see what duty cycle reading you get. Higher, go lean and vice versa.

BTW - you are changing the mixture, aren't you? You need to push the hex key down against the spring and feel it engage the adjuster. Sorry, I had to ask, it's easy to feel like you're turning the adjuster when you're not.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe