Glow plug light - PeachParts Mercedes-Benz Forum

psaboic · #1 05-06-2010, 10:43 PM

Tried the search and didn't find anything that fit my issue, so here goes.... Car is a 83 300D

Noticed today that when starting the car cold, the glow plug light came on, but did not go out. No buzzer either. I waited almost a full minute and the glow plug light never went out, so I turned the key. The car started normally, idled smooth, and as soon as it started, the glow plug light went out.

About ten minutes later, while driving, I noticed the glow plug light on. It stayed on for about 15 seconds then went off. About 3 minutes later it was on again for a few seconds then off. This on off cycle continued for my whole 30 minute drive. I shut the car off and about 15 minutes later I tried again.

Engine hot, same thing, glow light stays on until car is started. Glow light again randomly comes on and goes off while driving. Got home and waited 3 hours for the engine to cool before troubleshooting.

Here's the results. After unplugging the harness at the glow plug relay, all five plugs read at .8 ohms. Battery voltage of 15.55 volts is going to the glow plug relay, and at both sides of the the strip fuse (actually there is no strip fuse....the PO removed it and put a heavy gauge jumper wire there)

So, basically the system checks out, but why is the light staying on and no buzzer, and then randomly coming on while driving?

Glenn

1985300d · #2 05-07-2010, 08:53 AM

wow dude,
i would go find a fuse to put in there

could blow something if the HD wire dosnt melt and start a fire
cost alot for a new relay

then at least if the fuse blows right away,
you know the PO was covering up a bigger problem?

psaboic · #3 05-07-2010, 09:34 AM

A new fuse is definitely on the list. Is the glow plug relay strip fuse a 50 Amp or an 80 Amp fuse??

tangofox007 · #4 05-07-2010, 09:39 AM

Quote:

Originally Posted by psaboic

Battery voltage of 15.55 volts is going to the glow plug relay...

It might be time to buy a new voltmeter!!! Unless your battery has seven cells.

Quote:

Originally Posted by psaboic

Is the glow plug relay strip fuse a 50 Amp or an 80 Amp fuse??

80.

psaboic · #5 05-09-2010, 01:01 AM

The issue reared its ugly head again today. Worked fine at startup (light went out after a few seconds but no buzzer) and stayed out the whole 35 mile trip. But, after sitting for 8 hours, I went to start the car and the glow plug light came on but never went out after a full minute. I started the car (started fine) and the light went out. Started driving and the light came on and would not go out unless I pulled over, shut the car off, and re-started. Even then, it would come right back on in less then a minute. Finally, I got out and pulled the connector off the glow plug relay (the big one that connects to the glow plugs themselves) After disconnecting the connector, the light would now only come on randomly for a few seconds, then go out instead of staying on constantly.

After letting the car cool I checked the system again. Just like a couple days ago, all the glow plugs ohm out fine and voltages check out good.

What the hell could be causing the issue??? The only difference I noticed is that this morning when the system worked fine, the outside temperature was about 40 degrees, and both times when it acted up, the outside temperature was about 60 degrees.

Help

Glenn

rummur · #6 05-09-2010, 01:10 AM

Im not exactly sure how the glow plug system works on your car, but its gotta be somthing to do with the thermo switch that tells the relay when the engine temp is to cold and it needs glow plugs.

Follow the signal wires from the relay and find out where it gets its signal.. Its probably somthing that looks like a temp sender. then test the switch im sure its faulty, otherwise theres a short somewhere in that harness.

tangofox007 · #7 05-09-2010, 07:58 AM

Quote:

Originally Posted by rummur

Follow the signal wires from the relay and find out where it gets its signal.. Its probably somthing that looks like a temp sender.

Not on the subject vehicle. The temp sensor is in the relay assembly; it looks at ambient air temp, not engine temp.

Quote:

Originally Posted by rummur

Im not exactly sure how the glow plug system works on your car...

That would seem to make it difficult to diagnose the problem.

rummur · #8 05-09-2010, 11:22 AM

yeah yeah.. just trying to point them in some direction, better then walking in circles..

sorry for the misleading info though.

I wonder then, how does the relay know when to cycle off.. Does the ignition have a seperate detent for pre ignition and ignition?

kerry · #9 05-09-2010, 11:49 AM

Sounds to me like a failure in the glow plug timer. I'd get a junkyard relay, swap it in and see what happens. I'd also check to see if the plugs are actually being energized when the light it on. But I'm betting a different relay is in your future.

glenlloyd · #10 05-09-2010, 01:09 PM

Make sure when you test for ohms you check multimeter resistance first by putting both probes together. If your unit reports anything greater than zero you need to reduce your reading of the GP's by the same amount to get a real reading.

My guess is that you'll find at least 4 ohms resistance in the meter, or at least I would hope so. If all your plugs really test at 8 ohms then eventually you'll need to consider replacing.

Good luck

Steve A

tangofox007 · #11 05-09-2010, 07:03 PM

Quote:

Originally Posted by rummur

I wonder then, how does the relay know when to cycle off.. Does the ignition have a seperate detent for pre ignition and ignition?

In the original configuration, the relay cycles off when the key is released from the "start" position, unless the timer "runs out" (approx 30 seconds) before the switch is turned to the start position. The indicator light is controlled by the solid state circuitry in the timer and does not necessarily reflect the actual operating status of the glow system.

firemediceric · #12 05-09-2010, 09:38 PM

Maybe my trials and tribulations with a similar problem as chronicled here: Confirmation on GP relay issue, please will help you. Installing a volt meter in my car really helps me keep track of when power is being drawn and what the alternator is doing.

Here's what fixed my problem, and I don't think you can beat the price. http://www.**********.com/search/product.aspx?sid=hs5s44bd2mrn1n2cn4girt3v&partnumber=0250201953

That's part number 0250201953 at auto haus AZ

vstech · #13 05-09-2010, 11:05 PM

Quote:

Originally Posted by firemediceric

Maybe my trials and tribulations with a similar problem as chronicled here: Confirmation on GP relay issue, please will help you. Installing a volt meter in my car really helps me keep track of when power is being drawn and what the alternator is doing.

Here's what fixed my problem, and I don't think you can beat the price. http://www.**********.com/search/product.aspx?sid=hs5s44bd2mrn1n2cn4girt3v&partnumber=0250201953

That's part number 0250201953 at a

not nice posting competing pricing in a thread!
THIS FORUM IS SUPPORTED BY PARTS PURCHASES!

OP.
I would seriously check out your meter, if you are indeed reading 15.5 volts!
you could have an alternator issue, and a battery issue as well.
all of this could have damaged your controller.

psaboic · #14 05-10-2010, 09:40 AM

Ok, I'm pretty much convinced the relay is going. For the last three mornings, or when the temperature is below 50 degrees, the glow plug light works normally (on for about 15-30 seconds, then off. Start car and light stays off) Once the outside temp gets warmer you go to start the car and the glow plug light stays on indefinitely until you start the car. It will go off once the car is started, but come back on (and stay on) in about a minute.

What do you all think?

Glenn