92 300e Mixture issue

[Matt Laube]

1992 300 e 187 k miles. About 6 months ago the engine had a loss of power where the accel. would be floored and the car would fall flat. A temporary fix was a vac. leak and 15k miles later the scenario revisits . Oil in coolant- time for 30 -70 k head gasket change!

Symptom persists after gask renewal and cat. check. Car will idle normally when air pump is on ( rich) and then lose power after a few revs in warm up phase.

If you press on the disc on the intake the engine will richen and normalize.
EHA ? Some type of potentiometer in the fuel distributor?

Ideas. ? New ignition ,chain, valve seals and gasket. Vac. ga reading was erratic as cat was suspected but verified nonissue.

No issues with exhaust.

[optimusprime]

Well on some there is a potentiomiter and replacment is easy .Dont know what engine you have - M103 or M104 ? They have a carbon track inside that wears out over time.Replacment is the only option . Do you have a small micro switch on the throttle cable.If you have, then see if it clicks on and off .

[optimusprime]

And if you dont know ,at the top of the page you will see HOW TO ATICALS you will find a host of information on there . Very helpful, and thanks to PELICAN PARTS .

[Diseasel300]

Originally Posted by Matt Laube

Symptom persists after gask renewal and cat. check. Car will idle normally when air pump is on ( rich) and then lose power after a few revs in warm up phase.

If you press on the disc on the intake the engine will richen and normalize.
EHA ? Some type of potentiometer in the fuel distributor?

Ideas. ? New ignition ,chain, valve seals and gasket. Vac. ga reading was erratic as cat was suspected but verified nonissue.

You seem to have mostly identified your own problem. Vacuum gauge is erratic and pushing down the MAF disc will richen and normalize the running.

Since you recently did a head-gasket job, go back and make sure you used a NEW manifold gasket and that the bolts are torqued to spec. Check and make sure you didn't leave a vacuum line off somewhere.

The vacuum gauge should be reading a relatively consistent reading, it shouldn't be all over the place. Mixture control is a function of manifold vacuum on a K-Jet car. Ultimate mixture is controlled by the movement of the MAF disc in the inlet plenum. If you have air ingress from somewhere else, your mixture will be off due to both the mixture control being wrong and the ultimate mixture based on airmass being wrong.

Another possible cause, although a bit more unusual would be if you got the cam timing wrong during reassembly. Cam timing being incorrect can cause erratic or low vacuum issues.

When you had the head off, did you get the valves ground and their seats lapped? Adjust the valve clearances? If you have worn valves, seats, or guides, you can get some bizarre effects as well.

[Matt Laube]

Well....the problem has been solved. Yes, I did set the valve timing correctly, went through the head ( seals, checked valves for issues and lapped) set mixture with the Bosch Lamda box and used all new gaskets and followed torque specs. The driveability issue existed before the gasket replacement.

It was the Over voltage relay!

The one in the car was a cheap Chinese knock off and was very crusty and corroded inside.

According to my MB trained mech he said they are frequently a culprit for all kinds of oddball running stuff as they "talk" the ECU. The one off my 2.6 had the same part number so it was a simple swap.

Car has gobs of power and never has run as well.

Thanks at any rate!