I know, I know, another glow plug thread, but I'm doing my research on this using the search feature. Maybe I just haven't successfully found the thread about this.
Machine: 1985 300D Turbo, w123, 617, Bosch GPs
Problem: Car starts smoothly if I wait 8-15 seconds in pre-glow before starting. But the dash light does not come on. I know the GP's are working. But why doesn't the light come on? So I checked the following.
Continuity, voltage, resistance: The resistance on the plugs is under .7 ohms. The voltage on the fuse
and in the relay sockets and pins checks out. The GP dash light bulb works when the relay plug is disconnected.
Cleaning/Reaming: Took a glow plug out today using some thin 8mm and 12mm wrenches. It had some carbon buildup on it that I cleaned off. I don't have a reamer, so I tried using different drill bits in there. Nothing really came out. I'm going to take all the plugs out and crank the engine and see if any carbon shoots out. But most likely, the dirt doesn't seem to be the culprit.
Checking each plug: Still need to get a jump box and run current through the plugs to make sure they get hot.
What a certified MB tech thinks: I talked to the mechanic who sold me this car, and who knows a hell of a lot about these machines. He said if the light on the dash goes out, but the car still starts smoothly, then I shouldn't waste money replacing the plugs. I can just count to 10 during pre-glow like I do now, and in the Chicago winter I'll have to count to 20. He thinks the problem is with the relay timing. Is that true? Can replacing the relay fix this problem? I've read on this forum that if the voltage checks out fine in the relay box, nothing is wrong with the relay. Has anyone had this problem and just left it alone?
What I haven't done:- Hook up each GP to a jump box, see if it glows.
- Take each GP out and test resistance across it.
- Check the resistance on each GP's wire.
I didn't think I needed to do these things because
http://dieselgiant.com/glowplugrepair.htm only checks those things out for plugs where there is a continuity problem. Should I do these checks anyway?