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Old 09-18-2000, 01:02 PM
otto increment
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Howdy! I am new on this forum, so I apologize if I break from whatever convention exists, but please bear with me.

I have a 79 300TD (non-turbo) that put up a rather spectacular display of revving up uncontrollably and spewing out enough white smoke to completely obscure the road. (thats the short version, if anyone is really interested I will post the long version with all the gory details) I am at a loss as to what could have happened, but my intuition suggests that something in the injection system might have broken causing unrestricted flow of fuel into the engine. I am generally mechanically competent, but I am new to mercedes diesels and would really appreciate any suggestions or input.

I also will prbably end up taking the car into a shop to have it evaluated at some point, and I was wondering if anyone could recommend a competent shop in the Olympia Washington area. Taking the car to Seattle is not a problem, but obviously it would be easier if the shop was local.

Thanks in advance...


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Old 09-18-2000, 08:41 PM
Wm. Lewallen
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You should check the vacuum pump for a ruptured diaphram. Good luck. Bill L.
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Old 09-19-2000, 12:59 PM
otto increment
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Well you asked for it, so here is the whole story...

The day BEFORE the catastrophic display of smoke and noise, the vacuum pump failed. I spent a few hours thinking and looking, and determined that there were no significant leaks, and the pump was not doing its thing. The pump seemed to be putting air out of the line that goes to the air cleaner, but there was not a corresponding amount of vacuum on the other side of the pump. I decided that this was not a big enough deal to ruin our vacation, since as far as I could tell the only significance of loss of vacuum was harder brakes, no power locks, and having to shut off the engine manually.

The next morning, we were driving down a steep hill and I downshifted to low since the brakes obviously had no boost. We drove like this for a minute or two (long steep hill!!) and then all of the sudden the car started trying to accelerate without me giving it any throttle. I quickly shifted into neutral, at which point the engine started to race, and smoke started to pour out. I quickly stopped and popped the hood to shut off the engine. Pushing the manual shutoff was not as effective as it normally would be, it took a moment before the engine started to slow down, and then another moment or two to stop. Total time from moment of shifting to neutral to the engine stopping wasnt more than 10-20 seconds, but it seemed like forever!!

After the car was stopped, it started leaking oil rather severely from somewhere on the passenger side lower half of the engine, I havent had time to jack the car up and actually find out where, but the leak was enough to turn the tow dolly black with oil while towing the car from San Francisco to Olympia.

Thats the story... Last night I spent some time looking for a correlation between the vacuum pump and the injection system, and discovered that the pump is driven off the injector timing wheel. This leads to me current theory about the nature of my problem... It goes like this: Something broke in the timing mechanism that caused the vacuum pump to fail first, and then later the timing device itself. This caused the fuel timing to become advanced and/or more fuel to be delivered, which explains the sudden revving. The high RPMs caused the oil leak either through excessive oil pressure bursting a seal/line/etc., or excessive crankcase pressure due to high RPMs blew out a oil pan seal.

This theory may be improbable to those of you who know more about these engines, but in my ignorance it seems like a pretty good explanation.

It looks to me that I can remove the vacuum pump, and then the timing device rather easily, although the Haynes manual is unclear about how you re-index the timing device to the rest of the engine when you reinstall it, whick raises another question, what is the best service manual for this car? The haynes manual seems to cover brakes, tuneup, etc, but not much else... Should I go to the dealer and get the proper service literature?? Any suggestions would be appreciated.

Thanks again...

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Old 09-19-2000, 02:44 PM
Join Date: Aug 2000
Location: Holland, MI
Posts: 1,316
Sorry to hear of your trouble, and it sounds like a puzzle.

A word of caution; I understand that if there is an internal leak where engine oil can get into the combustion chambers, it can cause a "runaway" in a diesel! I have heard of this happening in stationary engines, so I suppose it could happen in a car.

The engine doesn't care whether you inject diesel fuel, or motor oil, and since the motor oil leak is NOT controlled, you get as much power out as you put oil in, ready or not!

I'd advise you proceed really carefully, up to and including having it towed to a technician for a better look.

BCingU, Jim

'96 E300D 60k mi (wife's daily ride)
'95 Audi 90 118k mi (for sale)
'92 GMC Suburban 138k mi
'85 300SD 231k mi (my daily ride)
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