I am perplexed and need the help of some of you old CIS guys.

I have a 1985 380 SE that I just got back runing. It sat for about a year waiting to get the block drilled, tapped and helicoiled after the head bolts pulled.

Anyway, the problem I'm having is that it cranks fine, and runs great when it is cold. It has plenty of power and runs smooth as silk. When it warms up however it runs very rough and won't pull a greasy string out of a cat's ass. As soon as the engine gets cold again it is back to running wonderfully.

I did a search for this type of problem and found a reference to "tweaking" the warm up regulator but I could not find this "tweak" anywhere. Does anyone know where to find this?

Any help would be greatly apreciated

Thanks

The most likely cause of this condition is a blocked catalytic converter.

Fuel pressure testing is the place to start on this car. Control pressure VS system pressure is the way acceleration on this engine is accomplished.

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MB Doc, I understand the fuel pressure controls this system.

Is there any other part of the system that is controlled by temp other than the warm up regulator?

I would first make sure that all vaccuum fittings and temperature sensors are connected, and that the O2 sensor is functioning.

You might also pull a couple of plugs out and see if you are running rich. You could have a cold start valve problem.

__________________
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

I'll second Doc.

fuel pressure test time, sounds like a bad warm up regulator but, with out checking system and control pressures through the warm up range and hot co/duty cycle readings you're throwing parts at it.


Joe

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OK guys here is the update, first of all the catalytic converter is NOT the problem, I don't know what shotgun fired that diagnosis!

I was thinking about the fact that the problem only ocuured after warm up, when we actually go into closed loop operation. For $20.00 i put in a new O2 sensor and bang, no more problem.

Now though I would like to center the fuel mixture, does anyone know how to measure and/or set the fuel mixture.

At one shop I worked at we had this cool little box that had an LCD readout and a red/green LED that pluged into the Diag port near the ignition coil. when the LED was green that indicated that the Lambda controller was controlling the mixture, then you set the mixture until the readout was 45-55 on the readout.

Does anyone know how to build this device, ours looked homemade from a radio shack project box.

Thanks

I have a book on Bosch FI at home - I am on the road this week - but I think I remember it said that you can set the Lambda with a dwell meter.

Glad it was a simple fix.

__________________
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