Once I'm started there's NO stopping me...

[glasgowkiss]

Good evening Merc Gurus.

My beloved 300D on a '92 plate has developed a pecular fault.

When I turn off the engine, everything stops and switches off...except the engine.

I'm having to use the fuel cut off lever in the engine compartment.

The car's revs drop considerably but she won't actually turn off completely with the key turning.

What's wrong? How much will it cost? Can I fix it myself do you think?

Cheers

Ken

 

[whitenemesis]

Something to do with the vacuum system, simple solution..

Some one more specialised will be along soon...

 

[Number_Cruncher]

As above, check the vacuum pipes and the connectors back from the injector pump to the vacuum switch which is behined the ignition switch. It's worth checking all the visible vacuum pipes because vacuum loss anywhere will make the vacuum levels in the rest of the system a bit marginal.

If you don't find a pipe that's rubbed through, or a rubber joining pipe that's perished, or a pipe that's coming off, you'll need to check the amount of vacuum in the system, and the vacuum tightness of the shut off valve on the injector pump itself.

It's highly likley that you'll find and fix this fault for pennies.

 

[glasgowkiss]

Hi

Sounds like a lot of dismantling then, but better that than a merc dealership and the labour charges.

Is it all quite easy to see, as I've no manuals or books to refer to.

Will try today!

 

[jaymanek]

im pretty sure the diesels have a simple shut off valve..

 

[Number_Cruncher]

im pretty sure the diesels have a simple shut off valve..

Yes, it's likely that this engine has a vacuum shut off valve which is mounted vertically on the back of the injector pump.

The unusual feature of the shut off systems of MB diesels prior to CDi engine is that they actually apply vacuum to shut the engine off. So, if there's a vacuum problem, the engine will just keep running.

Contrast this to almost every other car engine I can think of, where if the shut off wire comes off, the engine stalls.

This is the reason why these engines either have an accessible shut off lever, or, as on OM606s, where the manifold prevents access to the pump, a shut off tap on the fuel filter - because the main shut off is not fail safe. I don't think you would get away with such a design today in the litigious times we currently enjoy!