84 380 sl running very rich - PeachParts Mercedes-Benz Forum

polarisrmk · #1 10-12-2010, 11:40 AM

1984 380 sl starts fine when cold idles fine when cold. As it warms up idle gets about 100-200 rpm higher and black smoke coming out of tail pipe. Running very rich when it gets warm. When i put the car into gear idle drops and it starts chugging and then dies. very hard to restart if it dies. have to hold throttle to floor and crank. if i give it a little throttle when in gear it will not die but as soon as i let off the throttle it returns right back to low chugging rich idle. warm up valve? I have already verified that the cold start valve is not stuck open.

London380sl · #2 10-12-2010, 02:51 PM

It could be the oxygen sensor in the exhaust system.

polarisrmk · #3 10-12-2010, 03:09 PM

Quote:

Originally Posted by London380sl

It could be the oxygen sensor in the exhaust system.

I thought this but i have never had an oxygen sensor that went bad that caused the engine to run this poorly. The o2 light isn't on in the dash either not to say that that is any indication of anything.

abiby · #4 10-12-2010, 05:30 PM

Quote:

Originally Posted by polarisrmk

I thought this but i have never had an oxygen sensor that went bad that caused the engine to run this poorly. The o2 light isn't on in the dash either not to say that that is any indication of anything.

I can't be certain, but I believe on the '84 the light is mileage related rather than an indication of O2 sensor condition.

That said, my money says the issue is with the WUR. Of course that assumes they still had them in '84.

rowdie · #5 10-13-2010, 03:42 PM

I know the 560 O2 light is mileage related and it only works once so I assume the 380 is also. I think WUR also is the trouble. Check the vacuum connections first.

TAP · #6 10-13-2010, 04:28 PM

Not sure how similar your car is to my 87 560, but after several hundred dollars and three or four wasted months I found the problem you describe was due to a temp sensor which was giving bad readings to the ignition module. As best I could tell it functions something like a "choke" calling for a richer mixture when the motor is cold. Cost about sixty bucks and was a very easy replacement. Hope this helps.

ctaylor738 · #7 10-25-2010, 06:35 PM

The 560 and the 380 are different. On the 380, warm-up mixture is totally controlled by the WUR. Make sure that it has good power and ground. It is also possible that the oxygen sensor is bad so the lambda computer thinks the mixture is lean and is trying to richen it.