74 240D left me stranded today
 

Hi:

Was driving my 74 240D home from work today and all of a sudden noticed lots of smoke in the rear view mirror then the engine began running very fast and would not turn off. This is my first diesel Mercedes so things are still a little unfamiliar. Anybody have any ideas? Vacuum lines looked good and most of the little one way vacuum valves are new. Also, vacuum pump was rebuilt by previous owner last year. The only maintenance manual I have doesn't cover diesel engine troubleshooting.

Thanks.
Drew

Hmm
 

It sounds like a run away diesel engine.
Did the engine stop suddenly?

No. Engine kept right on running until I finally had to kill it with the clutch. It was quite an impressive cloud of smoke too.

Look at the 85 300d sudden oil loss thread just below this thread. It sounds like your engine may have been doing something similar: running on its own lubricating oil. This would explain the smoke and inability to stop.
The question is: why did this happen? Did you do anything different to the vehicle?

The broader issue is why is there a rash of these events? Has some cosmic karma turned against diesels in the last few weeks?

That was an interesting thread.
I haven't done anything unusual or made any modifications. Fortunately I stopped right away and got things shut down. There was still good oil pressure and proper oil level too, so if it was burining it's own crankcase oil, it didn't get through very much of it.

drewleroy, tell us more about your car. How many miles were on it?

i never took the injection pump apart in my '76 240 engine but
it doesnt shut off via vacuum. has a direct cable shutoff. all
that power and smoke means an uncontroled amount of fuel,
so something in the ip itself broke, probably in the rear section.

don

The car is in extremely good condition. It has had a string of obsessive owners and is well maintained. Mileage is something less than 120K. Exact value is unknown as speedo was changed out at some point by previous owner.

It transistioned into this mode instantly, there was no gradual decline or buildup of symptoms. One moment it was fine and the next it wasn't.

Thanks.
Drew

I had a throtle linkage spring break on my 74 240 D and it started to run away ,got it shut off with no damage.I had been messing with the linkage the day before..........

William Rogers..........

Suggest a test:
 

#1. Remove air filter housing.
#2. Get a smooth flat board to cover the intake.
#3. Inspect the throttle linkage, visual and manual, push - pull- jerk, look for binding - jamming - interference contact, under dash and hood.
#4. When you are sure the linkage is free moving, get an assistant to help with the next steps.
#5. Stand over the intake with board ready; but watch the throttle linkage at the injection pump.
#6. Have assistant start car.
#7. Do not hesitate to seal the intake with board, if it accelerates wild = over 1500 – 2000 RPM.

#A. Turn off with stop lever.

#B. Turn off with board.

If you feel confident to do this test, it will give you and us a lot of information.
Have a great day.

I believe this engine has a pnumatic governor with a rubber diaphram. I remember an old thread describing what happens when the diaphram breaks, but I can't find the thread at the moment. I remember it involves a lot of smoke, but I don't remember anything about a runaway condition. Maybe somebody can dig up the old threads(s) on the governor diaphram and see what's there.

Your vacuum pump diaphragm may have failed. I believe on this model, that permits oil to be sucked into the intake. Check the line going from the pump to the intake to see if there is oil in it.

Thanks for all the great advice. Hopefully I can get back at it tonight after work and see what shows up.

Kindest Regards.
Drew

drewleroy, first thing you do is look at the rear of the injection pump. If there is a vacuum tube from there to a box just upstream of the intake manifold (and no where else) then you have a pneumatic governor. If you have it and you have a gorilla knob (push/pull switch to left of steering wheel used to glow, start, and stop the engine) then you're in luck and the troubleshooting is pretty easy with a helper and a hand vacuum pump. You won't need to start the engine to check throttle linkage, governor, gorilla knob or linkage. Suspect an internal oil leak after the first three. Let us know what you have so we can get you started. I go away in a week for three weeks to climb smoke stacks.

dabenz, climbing smokestacks? hobby or profession?????????

William Rogers.......