Hi all--

The glow plug preheater light on the dash stopped lighting up yesterday, and now my car won't start. The starter turns, everything seems to be cranking, but the car just won't start. (1985 300TD wagon)

Here's how I got to this point: changed my headlights from sealed beam to H4 Cibies (60/55w) a few days ago, and a couple nights later the alternator light on the dash started to flicker (when the lights were on). After an evening of driving, car started fine the next day, but when I tested the headlights, the alternator light went on again. Next time I started the car, the orange glow plug preheater light on the dash failed to light. The car started fine anyway because it was still warm, but after sitting a few hours, it now won't start. The orange light doesn't go on, the car cranks, but doesn't start. The car is stuck in the lower level of the parking garage at my work.

If the alternator went out, is it possible that there's enough juice in the battery to do everything but pre-heat the glowplugs? Would that lead to these symptoms, and if that's the case, can I jump start it?

If that's not the case, does anyone have any suggestions how I can get the car started, so I can drive it out of this low-ceilinged-not-easy-to-get-a-tow-truck-in-there parking garage and take it straight to a mechanic for work on the alternator-glow plugs-battery-glow plug relay-whatever?

Thanks in advance for any quick responses. (Meanwhile, I'm studying all the posts here on what to do when the glow plugs aren't pre-heating)

have you checked the strip fuse on the glowplug relay? look real close for a hairline crack. Do you have a multimeter availible to you? To see of you are getting anything to the glowplugs.

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So everything electrical works except the glow plug light? Hmm....I wouldn't rule out the possibility of coincidence here, that the alternator light flickering and this problem are unrelated. Still, heck of a coincidence. When was the last time the GP's were changed?

When my glow plugs went out a few weeks ago, my light just stopped coming on, too, and I couldn't start the car. Numerous attempts at turning the key to the '2' position eventually got the light to come on, however, and then I was able to start. I would say try and try again in an effort to get back home or to somewhere that's not the parking garage. You might get lucky if you keep turning that key.

Good luck.

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Ralph

1985 300D Turbo, CA model
248,650 miles and counting...

you could have burned out your gloplug fusible link. mine is on the drivers fender well, close to the relay and such.temp fix maybe to use a piece of copper wire.ONLY TEMPORARY,THOUGH. if you can start it, it will run without an alternator, i believe.

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1984 123.193 372,xxx miles, room for Seven.

1999 Dodge Durango Cummins 4BTAA 47RE 5k lb 4x4 getting 25+mpgs, room for Seven.

Just for grins...
Try turning the key to glow position and using a watch to time it at one minute before trying to start the engine...

OK, there a few things you can check. It sounds possible that your alternator/voltage regulator has a problem, but that should not result in the glow plug light not coming on. In general, the glow plug light will not light if you have two or more glow plugs that are not functioning. If you have a multi-meter, you can verify if the plow plugs are getting power. They should be getting about 11 volts while they are glowing. If they are getting power, you can check the resistance of each plug by unplugging the cable from the glow plug relay to the plugs and measuring the resistance across each plug, they should be in the .5 to 1 ohm range. If the glow plugs are not getting power, take a look at the 85 amp fuse under the relay cover. I would also take a look at the fuses in the main fuse box. You may have also run the battery down, there is no problem jumping the car. Let us know what you find.

Thanks for all the quick responses (and please keep them coming).

The strip fuse in the glow plug relay APPEARS to be very much intact, but I'll try replacing it and see if that helps.

I don't know how old the glow plugs are. I bought the car last month with (seriously) only 40K miles on it, but I don't know when the plugs were last changed. But would this problem be happening if any of the glow plugs were still good? How many of them have to be bad before the car won't start?

These cars will normally start with a couple of bad plugs, unless it's very cold. I suspect that you have an electrical system problem that is preventing the relay from getting a signal. Checking the voltage at the relay would be a big help.

Where did you get a Mercedes diesel with 40,000 miles on it? Re-charge the battery whatever you do. Change or have the glow plugs changed as soon as possible. The alternator problem should be quickly solved, as well, with changing the alternator or connecting a loose wire being your most serious mechanical concern.

BenzDiesel

A 5-cylinder engine will usually start with one bad glow plug (if it's not freezing cold, etc.) and maybe even with two. You could have had one bad glow plug all along and not known it, I suppose, and then had a second one die. However, since the glow plug light is not coming on, I suspect it's not the glow plugs themselves but rather something else in the circuitry -- a fuse or the relay itself. While you're checking things, make sure the glow plug light itself is good.

Jeremy in Santa Rosa, California

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"Buster" in the '95

Our all-Diesel family
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When it got cold this winter I had a really hard time starting my 300TD with one bad GP. Changed the bad one and she would start right up. So you could possible have had one and and a second recetly go out causing the hard starting.

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When I changed my plugs I realized that one or two of them must have been bad all along, as the new plugs made it sound much smoother on start-up. I would guess you have bad plugs.

By the way, if you are going to change them yourself I would highly recommend investing in a 12 mm ratcheting wrench.

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Ralph

1985 300D Turbo, CA model
248,650 miles and counting...

the car will try to start with several glow plugs bad. it'll chuff and chug and such, and might start if 2 cylinders are firing enough to increase engine speed enough to fire the remaining cyl. check the glow plugs and if necessary jumper a large wire from the positive batt terminal to a single glow plug or that strip fuse. it'll feed all the plugs from there and hopefully allow you to start the car. I have a fully manual secondary glow plug controller and relay that works in parallel with the factory system and hasn't damaged the original controller despite backfeeding it.

karl

.5 to 1 ohm range

At room temperature, or when the glow is fully heated?

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1992 300D 2.5 turbo diesel. 319 k miles.
124.128 chassis, 602.962 engine, 722.418 tranny.

At room temperature (or garage temperature) the resistance is less than 1 ohm. It goes up significantly as the temperature of the GP increases. I don't know how you would measure them hot anyway. Normally the resistance just goes to infinity when they fail.