My normally reliable '92 400E has become undriveable. It starts and runs Ok when cold and for a little while until it warms up. After it warms up, there's no power, engine misfires, backfires when accelerator is pressed; and if it stalls may not start again until it has cooled off.

The plugs look fine and engine has about 210k miles. Check Engine light is *not* on.

I've searched this forum and the web and haven't found anything that fits yet.

Could a bad catalytic converter cause this behavior?

Any hints / tips on how I can diagnose this problem will be appreciated.

Thanks,
-Forrest

I found a possibly related post:
http://www.peachparts.com/shopforum/showthread.php?t=243476

But ultimate solution was not included

Anyone know what fixed the problem for 'February'?

-Forrest

Hi There:

Try checking the crank position sensor.

Eric

__________________
1987 260E Charcoal Grey 157,000 Miles
1987 260E Forest Green 120,000 Miles

Eric, thanks for the reply.

The engine runs great when cold; wouldn't the crank position sensor affect running at any temp?

-Forrest

Hi Forrest:

I had the same problem twice and changing the sensor solved my problem. When the car got to operating temp, it would shut down and crank but not start. Wait 10-15 minutes and starts up and goes until gets up to the same temp and shuts down once again.

Eric

__________________
1987 260E Charcoal Grey 157,000 Miles
1987 260E Forest Green 120,000 Miles

You are closing in on it. If engine starts and runs when cold, then stumbles to the point of undriveability when warm you obviously have a temperature related problem. A similar condition on my M117 engine (560SL) was caused by a failed engine temperature sensor. This is the sensor that inputs to the engine control computer. Don't confuse it with the water temperature gauge sensor or the cooling fan sensor.

I would check that sensor using the cold/hot resistance readings given by your tech manual. The sensor is not very expenive ($30 or so as I recall) so if you want to just swap it and hope to get lucky you could try that without being hurt too badly.

Let us know how you fix this problem, it adds to the body of knowledge.

Eric, is there a way to check the CPS before replacing it or any other symptom of a malfunctioning one?

Thanks,
-Forrest

Rocky, unfortunately, I don't have a 'Tech Manual' but will try to locate the data online. Any idea where the ECU temp sensor is located on an M119?

Thanks,
-Forrest

Not a clue but should be screwed into the intake manifold somewhere. Mine is a brass hex-shaped item about 1 inch across with two wires attached. Different engine of course.

If you are going to do a lot of troubleshooting and repair on your car, I can recommend a subscription to "alldatadiy.com". It is inexpensive and you will find a wealth of information. You may also like a repair manual on CD available from many sources. I got mine from an ebay source.

Good luck!

Forrest,

I know this thread is 3 years old, but did you figure out what was the cause of the problem with your 400E?

Thanks