Just joined this forum.
I'm the owner of a 1990 W124 300 Diesel.
The last 15 years the car did an outstanding job. It never failed and
maintenance costs were surprisingly low!
Recently problems started with stopping the motor. After turning the
ignition key in the off position the motor is still running for a few
The time the motor is running despite turning the key in the off
position becomes every day a little bit longer.
I'm afraid that the moment is near that the motor won't stop at all.
It would be great if somebody could advise me how to solve this
AFAIK, the MB Diesels have a fuel valve that is controlled by a vacuum
hose that runs to the ignition lock. The problem could be with the
valve, the hose, the ignition lock or the vacuum in general. I think the
valve that shuts down the fuel supply is the most likely candidate.
You'll get lots of advice here. In fact, I'm sure someone will correct
my post any time now. I (also Dutch) have a 250D but I've never had any
vacuum problems yet. Fingers crossed.
Our three weapons are fear, surprise, and ruthless efficiency...
and an almost fanatical devotion to the Pope....
Classic symptom of either a vacuum leak or failing shut down device
(vacuum powered bellows on the old cars, I suspect the same on your
model). Vacuum leak in old cars is often in door locks - sufficient to
prevent engine shut down - may also be so in your model IF it uses a
vacuum powered central (door) locking system.
There's probably a STOP lever on the engine's throttle linkage that
you'll soon need to use so take a look for it now rather than some dark
I think this is OM603 motor, and the door locks are not controlled by
the same vacuum.
On top of the injection pump, there is a round "bell" (sort like a
smaller bike bell). It has a vacuum tube attached. Disconnect the
tube. Use a vacuum pump to draw air from the "bell". It should hold
vacuum for at least 30 seconds. If not (most likely), this fuel shutoff
diaphragm needs replacing.
If the diaphragm works fine, you need to trace the vacuum route. Does
the climate control work fine? And power brake? If both fail, then it
is likely the vacuum pump (front of engine, same axle as injection
pump). This pump is not like the old one on OM617. It cannot be
rebuilt and is quite expensive.
Many thanks for your help!
I did check the vacuum of "the bell" and it didn't last for 30 seconds
at all. After approximately 3 - 5 seconds the vacuum was gone. So
accordingly your advise it must be the diaphragm.
Is it possible to replace this diaphragm only or do I have to replace
the complete "bell"?
Although I do normally all the maintenance and repair myself I'm a
little bit worried about the question if I can replace the diaphragm or
the complete "bell" myself. I know the fuel pump is a complicate device
and if I ruin it by trying to replace this item it will be a very
expensive repair by the garage!
Has anybody experience or knowledge replacing these items?
Sure. you replace the while thing, which is cheao. It comes off
with two bolts and should take you maybe 15-30 minutes to do it.
It can be a bit of a bugger to put it back on, but everybody
maages to do just that after cussing for about 10 minutes.
You can't ruin the injection pump by doing this (unless you
let sand get in it while the bell is off. Rather unlkely to happen)
Need Mercedes parts ? - http://parts.mbz.org
Richard Sexton | Mercedes stuff: http://mbz.org
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