Hello all, Just got another 240d, this one is a '83. Its got a few problems, but the first one I need to get at is getting it started in this cold weather. The glow plug light does not come on at all, when 1st trying to start, but after I get her going, and running for a while, then stop. the glow plug light works like its suppost to, and she starts right up. Is she telling me to replace the plugs ? Or the glow plug relay ? thanks

Maybe a combination of things. Youc an test the GPs using a volt/ohm meter and then check the current coming fromt eh relay to the plugs.
Sounds semi-intermittent enough that I would recommend checking the stripfuse at the relay. They sometimes look good but have broken ends. It is easy to check by removing two phillips screws. Might be that after the engine compartment warms the strip fuse makes partial contact.

I'm guessing a little here but those are cheap diagnostics.

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

Check and clean all of the grounds. Cold and contracted and poor contact, warm and expanded and better contact. All of them means per-the-wiring-diagram. After that it's a matter of finding the broken/corroded wire or connector, as Fisherman stated.

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daBenz - 1970 220D

Thanks for the quick replies. It must be a wireing problem, this morning I went out to try to start her up, I had the block heater on for the first time, had it on a timer to start at 3 this morning. Well, went out and turned the key, and the dashlight for the glow plugs came on, cycled off, and she started right up. Too wet and cold right now to track down. thanks again

Linsky.

The GP dash light works intermittently on my '79 300SD, but the GP are working correctly.

Observe the overhead cabin light when turning the key on. If it dims slightly, that tells you that the GP are being energized. They should stay energized for about 40 seconds then shut off.

Only a blinking of the GP dash light after the engine starts indicates a bad GP.

P E H

Went out to try PEH"s overhead light-energize GP idea, and got no GP light and no difference in overhead light. Try to start anyway, but battery went dead. Charged it up a few hours, and went to try it again, this time the GP dashlight came on, I couldn't believe it, so I cycled the GP again, and she started right up. Could this be just a bad battery ?

Actually, if one or more glow plugs don't work, the amber instrument cluster light won't come on at all. It acts as a crude trouble shooting tool to tell the consumer/driver that something's wrong. If it flashes after having started the engine, that too means faulty glow plugs at least (maybe even a faulty g.p. relay ??).

Linsky,

Did you notice if the overhead cabin light dimmed the time the engine started? If it doesn't dim, the GP aren't working which is probably caused by the GP relay not working or the fuse in it is intermittant.

If your battery went dead with out cranking the engine for at least 30 seconds after charging, its time for a new battery especially now that the winter is coming.

It could also be that your alternator in not putting out enough voltage to charge the battery properly. Check the voltage with fast idle engine, it should be at least 14.3 volts.

If you need a new battery, I suggest a group 49 from AutoZone. $60 + tax for a 7 year warranty battery is a good deal to me.

P E H

Ive tugged and pulled every wire under dash and to and from the GP relay, trying to find a short, but nothing obvious. Seem like it might be in the ignition switch, anymore ideas ?

I'd check that ground strap from the starter to the unibody. Pull both ends and do the clean, bright, and tight thing to those connectors. Same thing for both ends of the battery cables. I still think you have a corroded connector - those grounds are the first to get dirty and the first place I look, after I know I have a good chassis ground via the starter and battery. Then, when the dash light doesn't come on, check for power at the relay box - power to the box, power out of the box to the plugs.

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daBenz - 1970 220D

The first thing that I would do is make sure that the glow plugs and the relay are good. New plugs are cheap.

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N. Hodges
1994 S350
1987 300 SDL (for sale)

Check the 80 amp strip fuse in the glow plug relay - it could have a hairline crack. Loosen the screws and take the fuse out to check it. Be careful, as it is always "hot", not disconnected by the key switch.

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Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References

N Hodges,

You think about $12 per GP is cheap. I don't.

P E H

To each his own. Compared to the time wasted trying to find a short that may or may not be there, $12 is cheap. For $48 you get a working system and save a day or two. You pay your money and you make your choice.

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N. Hodges
1994 S350
1987 300 SDL (for sale)

N Hodges,

My choice is to replace only the bad GP and save $48 (I have 5 cylinders) since a GP is like a light bulb: it either works or it doesn't.

Maybe I could get you to send to me all the good GPs you throw away.

P E H