Ok - scared the crap out of me this weekend.

I've owned the car for about 6 months now - been great - no issues.

This weekend I wanted to check the condition/model of the vacuum pump so I pulled it and the fan off. Replaced everything - all good.

Started the car to test - idled fine. Walked away for 4-5 min's and was in the garage and the engine jumped to max RPM. Engine screaming - black smoke - the whole thing.

Jumped into the car after only 3-4 sec's of this and turned the key. Engine stopped - thank goodness. Sat there for a few min's - replaying all the things I've done that weekend that could have caused this - nothing.

Started the car again - idle was fine. Drove it for the rest of the day - everything was normal.

What happened?

-John

Call Roy...

I cannot think of anything that would result in max rpm from what you've done.


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We look forward to hearing what comes of your conversation with Roy.

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I don’t know what it was, but I do know what it wasn’t. It wasn’t a true RUN AWAY. The only way to stop a true RUN AWAY is to smother the intake and cut off the air, completely. Or cut the fuel line and allow the fuel to burn off, unless it is crankcase oil that has ignited and then cutting off the fuel will probably not help, which is why you have to have an object to cut the air. On a real RUN AWAY, the next time you start the engine and haven’t fixed the problem, the engine is going to RUN AWAY again, no ifs ands or buts. And I doubt you would have run towards the car, once it was in RUN AWAY mode, unless you were really brave, when you didn’t already know what to do to kill the air to the engine.

If the car starts and drives fine now, you are probably o.k. You may have a leaking injector or something that allowed fuel to pool in a cylinder that had to be burned off, that caused the high revving, but it was not a RUN AWAY. A RUN AWAY is just what it says: A RUN AWAY, completely, FULL SPEED REVVING, out of control. The good thing is most folks couldn’t intentionally cause a real RUN AWAY if they were trying to do so to save their life.


However, I would still have the pump looked over by somebody who you really trust that they know what they are talking about.

BenzDiesel

I had a great long talk with Roy - great guy.

He gave me several things to check - many of the traditional "run away" causes related to leaking oil around the turbo, check for oil in the cross-over pipe, etc.

I agree - I don't believe it was a "true" run away after talking to Roy. The fact the engine DID shut off and the RPM's were steady at 5-6k RPM and not climbing...

Roy suggested it may be the cruise control - which is already flaky on the car - so I'm going to pull the linkage off the cruise control today.

Thanks everyone,

-John

Although your problem wasn’t a true RUN AWAY, your description indicates that something abnormal did happen that you need to find out what. It is very difficult to get these cars to rev over 5,000 rpm. Not to mention getting one to rev to 6,000 rpm and then have the rpms to stabilize in that rpm range. When my cars RAN AWAY, I don’t know what the rpms were, but it sounded like a jet engine taking off, so I can safely say that is was well above 6,000 rpms. On another one, I just let it go to see what would happen and the piston tore a hole out the side of the block after the engine revved so high as if it was a LIVING THING. Also, the smoke was white and hung in the air like a giant cloud over head, slowly falling back to the ground.

If you find out how to get a controlled 6,000 rpm on one of these cars, would you please post. Guys are now trying to hot rod these diesels and getting them to rev high in a controlled state is one of the problems I see or read that they are having. Whereas, you had a case of controlled high revving that you didn’t want. But, your case shows that it can happen, high revving while being controlled or limited.


BenzDiesel

that happened to me on my 300SD; cruise control just set to full throttle for no reason while i was in a parking lot. very scary. never had a problem after disconnecting the cruise control linkage.

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The cruise on my wife's 300E liked to behave weird also, I have since unplugged the actuator under the hood for safety. At least on the gassers it will rev limit with the computer if the throttle gets maxxed. The diesels aren't so lucky in that regard

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I thought the injector pump had an internal governor. isn't that what you check when you do the unloaded RPM check? See 07.1-105

Roy mentioned this is as another possibility.

-John

Yes, his Governor did the job it was supposed to do and limited the max RPMs.
On most Inline Fuel Injection Pumps the that High Idle Speed is adjusted at the full Throttle Stop.

Run Away = Stationary Italian Tune-up

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