1993 300SD W140 glow plug issue

[mccark]

Hi all,

Been reading the posts on all the glow plug issues but still have questions.

Problem:
Turned the key, waited, no glow plug light, waited some more, started up (it was warm). After 10 seconds of running, glow plug light came back on for several minutes while driving before going out.
That was yesterday.

Today:
Turn key, wait, no glow indicator light. Started, but obviously forced, started very rough. (not going to make a habit of that) Glow plug light came on after startup, then went off. Let it run for 15 minutes until warm, stopped engine, turned on ignition, no plug light....

Question(s):
Is this a sign of a relay not dropping in/out of a circuit?
Are glow plug circuits in series or parallel?

What's first, clean the relay contacts and check the fuse?

Bosch shows 16.83 ea for plugs, seems reasonable, but I am unsure of my options.

Lastly:
Thanks,
kevin

[sixto]

I'm pretty sure a 93 SD glow relay has an automatic circuit breaker. If so, there's no fuse to check.

Get your hands on a wiring diagram so you can check power and ground.

Sixto
87 300D

[bigbillyboy]

any resolution on this issue?

[larry perkins]

i know the 91 had a glow system that had diagnostits,if you got a bad plug, the light will come on about 45 seconds after you start the engine.
larry perkins lou ky

[VegStew]

I know its a different beast, but the gp light on my 90 300d just started doing the same thing. It also uses no gp fuse. After testing i found 1 of my gps to be bad. Still starts, it just takes a few secs or so for the idle to smooth out.

[Fulcrum525]

Again not the same but my 91 did the same thing, turned out to be a bad glow plug interupting the circuit.

[compu_85]

Yup, the glow plug relay is "smart", if plugs are bad the light won't come on before you start the engine and then will remain on after it is going.

-Jason