For the past couple of weeks my 81 240D has been very hard to start. It takes about 10 cranks to get it start when the engine is cold. I h ave no problem when the car has been driven for awhile and is setting for a couple of hours it starts right up.

I replaced the glow plug relay has I was thinking that it was the issue, but it wasn't has it still very hard to get it started. The glowplug light, lights up like normal.

Any ideas?

So, having replaced the glow plug relay without the benefit of any proof that it was bad, have you tested the new glow plug relay to verify that it works?

Since the dash light lights up, probably the first place to look would be to see if you're getting voltage to the glow plugs. Check them all. If that looks good, maybe you should check the glow plugs themselves. They do go bad, and one bad one out of four is enough to give you starting problems on a cold day, especially if the engine is not in top shape.

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'79 240D

Check the actual glow plugs themselves first. If there is an issue with the glow plug circuit they are the most likely suspect.

Do you have the early series plugs or the smaller parallel ones? The series are identifiable by having some squiggly wires between them.

Have you done a valve adjustment?

How old is the battery?

Ever clean the ground connections?

How are the battery cables?

Oil change recently?

Any alternative fuel use?

New black primer pump or old twist style?

Condition of air filter?

Fuel filters changed last?

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Changed out the secondly one about 2 days ago.
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I changed the relay out because the dash light wouldn't come on. I test the plugs and one of the them appears to be bad, I have the series plugs.

I'm looking at upgrading to this Back to the* Mercedes Diesel parts for sale


Is this a good kit? How hard is it to do this?

I would suggest doing a valve adjustment and see how bad they are...

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Do you have loop style plugs? I'm pretty sure an '81 would have pencil style already. Not 100% sure tho.

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Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"