My 89 benz cuts off at 20 mph. - 1989 Mercedes-Benz 300-Class

every one is having trouble trying to understand what you are saying
cannot fire or raise ----does that mean cannot accelerate the engine
beyond 20 odometer does that mean faster than 20 mph(klm ph)
or does it simply mean that it will not rev higher than 2000 rpm on the tachometer
a odometer reads speed and a tacho reads engine rpms
so you can see why no one is answering your question
it is confusing as to what you are saying

Cars produced in Germany are electronically speed limited to about 150 mph. This is embedded in the software. If there are no other problems with the engine, fuel or transmission it is possible the management system has been remapped and the speed limiter has been reset to 120 mph.

Have you tried changing the transmission filter and fluid?

it may be time for an overhaul

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Dirty wheel speed sensor on the front wheel clean or replace. Or it maybe the cruise control amp, if its that find a bone yard to get a replacement.

What are the RPMs at when it's at 20 MPH?
I would personally start listening for vacuum leaks. That's a quick easy fix.
The 89 is notorious for problems with the TPS sensor (throttle position sensor) and the idle air control valve thos are also cheap easy fixes.
What do you mean by bog down is there any shuddering involved?
Shuddering this could point to a short on the engine block.

Sounds like a fuel problem, like a filter or pump problem, but don't be surprised if its your catalytic converter. Good Luck =)

Hi

Does the engine spin over OK, but just will not start ?

If so, check for a spark to the spark plugs, if that is OK, remove the plugs, inspect them for wetness & oil, check for compressions in the cylinders, if that´s OK, are you are getting fuel to the injectors.

Good Luck !

Let me know how you get on.

Don´t forget to give me a FixYa rating please !

John.

its a faulty speed sensor or plug to speed sensor could be dirty

Sunflower Hi...My ESP light is on and while I am driving my wheels lock. What could this be? It started doing it while I was driving about 20 or 30 mph but now its been also doing it while im going about 40 to 60 mph.. It almost caused a really bad accident. Someone please help!! Im desperate!! I have a 2002 Mercedes C320.