I'm having a problem with my diesel. It's a 1985 300SD, and it won't start. At first it started having intermittent problems where it wouldn't start, then i'd turn the ignition key off, wait, then turn it back to on and it would fire right up[:@]. I noticed during all this that if the glow plug light did not light up, it would crank and crank but not start, then if the glow plug light would miraculously light up, it would fire up like normal no problems. Is there a common problem i should look at or test related to this? I've heard of the glow plug relay going bad, but wouldn't it need to be cold out for the glow plugs to make a difference as to whether the car start or not (this was occuring when it was still 80 degrees out here in NM)?

 

sounds like the glow plug relay

you need those glow plugs whenever the engine isn't warmed up, no matter how hot it is outside
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Hmmmm, didn't know that. I thought this car would be similar to the TDI i had, when the glow plugs didn't work it would start rough, but always start. I guess i have some electrical troubleshooting to do........

 

test the glow plugs...there are many good threads available for accomplishing this.

 

I found the problem. I tested all 5 glow plugs and they are all within .6 to .7 ohms. However when i pulled off the cap on the glow plug relay, the 80amp strip fuse was broken in half. What's really strange though is that it's not burned at all, the edges of the break are clean, almost as if it was cut. Is it possible that the vibration caused it to break, and not a short in the circuit?

 

Your fuse did what it was suppose to do if you had a short or an overload. If it was blowen and you wereable to start car nevertheless...that means your engine's compression is most excellent.