RobertS

I have owned a 1993 Mercedes-Benz 400SEL for about two years now, however I've spent the last year trying numerous times for the closest dealership to repair what they called was a bad computer or relay.
The initial problem was that the car would not respond to when the accelerator was floored to the ground, in what normally would have been the passing gear. Gradually, this problem became worse and the car began to lose speed on hills and I can only press the accelerator down so much before the car stops responding to the acceleration. Basically, if I press the gas too much, the car acts as if it is in neutral. And, once reaching speeds of 80MPH+ (about 3RPM) the car violently jerks and the RPM gauge jumps.
About three new control units, a throttle control actulator, and a new electrical engine harness later, I still have the same problem with the power loss. The dealership still thinks that it is a problem with a control unit, however each new one they try still does not fix this problem. The last attempt, the manager over service mentioned something about my car not being a "typical Mercedes-Benz intended for use in America".
Thanks for taking the time to read this. I just would really want my car working again in its normal state. If anyone knows anyone who would know how to repair my car please reply back or email me.

Jer

Your '93 400SEL is actually a W140. You should post your problem in the W140 forum for better help.

If the car is violently jerking and the tach is bouncing, the transmission is up-shifting. Down-shifting is usually smooth. You can adjust the shift modulator on the transmission to effect firmness of shifts. Is there a kickdown switch behind the accelerator pedal?

I believe your car has the Bosch LH Jetronic injection system. It uses a CAN, Controller Area Network, to communicate between various control units. They are the base module, ASR/ABS control unit, LH injection, electronic accelerator/cruise control/idle speed, and the diagnostic module. Which ones were replaced?

RobertS

Thanks for the reply. My car only begins jerking whenever it reaches around 80MPH (making it impossible to go any faster). The rest of the time, the acceleration problem is just that I can only press the accelerator a certain amount before the engine stops responding and there is no power. Some days the car will seem to have much more power than others.
I do believe my car has a kickdown switch behind the accelerator pedal, but the problem with the acceleration is not just with the kickdown. After pressing the accelerator down not even half way to the floor, the engine begins to act up and stop responding (RPM Gauge does not even rise, even when accelerator is pushed to the floor).
The first time the Mercedes dealership replaced two control units, they were what they called the EA Control Unit and something like a Throttle Control (it's hard for me to remember because this has been over a year ago). After this, they replaced the electrical harness and the throttle body value. Recently, they replaced what they called the "Left Hand Control Unit" with Part# 021-545-71-32-81, however this also did not solve the acceleration problems. Another interesting note the dealership made was that my car did not have ASR.
I'm not sure what the problem is, but after a year of having this dealership attempt to fix my car over and over, I am really beginning to lose faith in them. However, I don't believe there is any other Mercedes repair shops in the Lexington, KY area that could help any more than the dealership so I turned to this forum. Any advice or reply is greatly appriciated.

Jer

Check some of the basic things, like injectors and spark plugs. The injectors work best when they are cold, but as the engine warms up, leaks can form around the injector seals. Sometimes the mechanics of the injectors simply get worn out, too. This can lead to loss of power, as you are experiencing.

RobertS

Thanks for your input. Today, the dealership called (they've had my car for about two weeks now troubleshooting) and said they believe the pinpointed the problem down to one of the fuel pumps malfunctioning. After replacing the fuel pump and test driving, the dealership told me that this resolved the acceleration problem. I won't be able to pick up my car until tomorrow, so I won't believe this until I drive it, but I hope this was the problem.
I will reply back tomorrow evening on the condition of my car. Again, thanks for your help.

keithmccarver72

I had that problem it worked it self out driving on the express way it took a while I think we dont work these cars hard enough there built to be driven and I baby mine I had that suddle shake and acceleration problem just wanted to share good luck buddy