1993 300TD Glow Plug Light

[230K]

Hi

Wifeys 1993 124 300TD is behaving funny, she has failed to start twice in the last 3 weeks or so.
When it fails to start the glow plug light doesnt light prior to cranking. It cranks over fine but will not start.
On the last couple of occasions while i was at work i have told her to put it on the charger for an hour and sure enough when she turns the key the glow plug light will illuminate as it should.

Could there be some sort of voltage sensor that decides if the battery voltage is low that it decides not to click in the glow plug relay. Seems strange that light will not illuminate but once it gets a bit of a charge it does. maybe it is just coincidence. Anyone had probs like this before?

When the relay gives porbs is it usually intermittent??

My problem is that car doesnt not illuminate the light when i am about so i can't get the meter out to check what is not getting power. Any time i try it the light comes on no prob.

Anyone?

230K

 

[Dieselman]

Wifey is behaving funny, she has failed to start twice in the last 3 weeks or so.

There is a happy man..

 

[Dieselman]

Sounds like the glow plug relay is going duff. I can't see it sensing battery voltage so try cleaning all the contacts.

 

[230K]

Hi

The first time it happened she was stuck outside a friends house and i came to the rescue, i tried tapping the relay to get the light to illuminate but it didnt help, i thought if it was dirty contacts a tap would have helped. That is the last time it has mis-behaved when i am around.

I have a 5 cylinder relay from a 190, would i be able to make it fit to eliminate the relay as a trial? Has anyone done that?

I might have to bite the bullet and take off the relay and have a look.

230K

 

[Dieselman]

I have a 5 cylinder relay from a 190, would i be able to make it fit to eliminate the relay as a trial? Has anyone done that?

That would probably fit.

The glow relay is a timer relay that uses the engine temperature sensor to decide how long to pre-glow (orange light) for.

 

[230K]

Hi

I just went out and pulled the relay, opened it and cleaned the 2 main contacts with emery paper. They were clean enough anyhow bit i gave them a rub. The half a dozen or so little ones were fine so i didnt touch them.

The 5 cylinder i could have made fit but it would have meant breaking off 2 lugs to allow the conectors to fit (one was a dummy for the 6th cylinder but was too big to fit the plug) and as its on loan from brother in law i didnt want to just yet.

The 5 cylinder one had one less connector or the accuator plug labelled "T" on the 6 cylinder, maybe it doesnt have the temperature sensing facility?? Could it be a temp sender on the engine that is causing the problem??

230K

 

[Number_Cruncher]

>>pre-glow (orange light) for

One thing I've been watching and learning on my 1995 E300D is that the glow plugs stay on for much longer than the dashboard light. If you switch on, let the light go out, and just wait, you'll hear a click after about 45 seconds, and the dash lights will glow brighter.

The glow plugs run for much longer than the light, and if you want to get more heat in, instead of glowing twice as many do, just leave it to run a bit longer.

This behaviour seems to be quite general for old-tech indirect injection MB diesels.

 

[Dieselman]

All diesels with glow plugs work like that. The stage after the light goes out is called post glow. Really it's post start glow.

This ensures continuous running and low emissions during the warm up phase.

 

[Number_Cruncher]

Yes, quite so, the point I was making is that the glow does continue after the light goes out - many people think that the glow stops when the light does, and they think that to get more heat, they need to switch off, and start again.

Many makes sense the engine has started, and apply a reduced voltage post start glow, which can remain on for a significant time.