W123 240TD - engine very slow to switch off

[shivayash]

Dear All,

My engine takes ages to switch off, to the point that I take the key out and after about 2 minutes it coughs until finally stalling.

Any thoughts?

Best wishes,

Shivayash
(mercedes newbie)

 

[star]

You have a leak in the vacuum system, its a matter of isolating it, could be anything from the shut off cell on top of the pump to a major leak in the c/locking sytem. A vac pump with guage would be helpful in diagnosing this.

 

[brandwooddixon]

I'm sure that you'll get a reply from someone more knowledgeable than I, but I think that this is due to a vacuum leak.

It may not apply to your car but I'm sure that I've read on here about other diesel vehicles which wouldn't turn off and it's commonly down to a leak in the vacuum system used to actuate the fuel cut off.


- Damn pipped to the post!

Another problem could be oil leaking from the turb into the intake, but this sounds unlikely given your description.

 

[wireman]

I have had this problem, mine was the pneumatic stop capsules diaphragm had failed (£20 from bosch).

There is not much to the stop system, a vac pipe goes to the "ignition switch" actually its a 3 port valve on the steering lock body and the "switch" puts a vac onto the fuel pump mounted capsule via a second vac pipe to stop the engine. In the on position the engine side of the valve is closed off and the fuel pump side is vented to atmosphere.


Lift the 4mm pipe off the fuel pump and measure the vacuum when the ignition is turned off, it should be at least 20 inches of mercury, 500mm hg. The vac should remain for some considerable time after the engine is stopped by using the lever on the pump. if this vac exists its the capsule, if it is low its a either leak on the pipes or "switch" or a duff vac pump (which could also cause poor brake servo asistance).

The 4mm nylon vac pipes are joined with short rubber hoses which can split and leak or fail completely.

If you dont sort it out the coughing engine will evenualy tear the engine mounts apart.

Dig around the forum there is more info on this.

 

[Bolide]

I think I'm right in saying the W123 has a vacuum accumulator (a small tank that contains lots of vacuums...) and that they tend to leak. Whatever, look for a vacuum leak

Nick Froome
www.w124.co.uk

 

[stever]

I think I'm right in saying the W123 has a vacuum accumulator (a small tank that contains lots of vacuums...) and that they tend to leak. Whatever, look for a vacuum leak

Nick Froome
www.w124.co.uk

You're correct that there is an accumulator - it's underneath the parcel shelf. All the leaks I've come across are due to other problems though - usually split diaphragms on the various actuators, or cracked pipes.