My glow plugs are smarter than I am. - PeachParts Mercedes-Benz Forum

Ben01 · #1 09-23-2007, 08:06 PM

The car: 1984 190D, 5spd, 180k miles

The Problem: Glow plugs stopped functioning. Dash indicator doesn't light and the engine refuses to start without prolonged cranking.

What I've Done: Metered out the GP timing relay box. It's getting 12V. Changed all four glow plugs. Problem still persists.

What I'd like from you: Suggestions on what to test and/or replace next.

Brian Carlton · #2 09-23-2007, 08:11 PM

Did you check for 12V at one of the plugs when the key is put into the #2 position?

If you have no voltage at the plugs, the problem is either the relay or the ignition switch. There is usually a violet wire that has 12V when the key is first put into the #2 position. This signals the relay to close.

You must determine if the relay is not functioning or the ignition switch is not providing 12V to the relay.

JimSmith · #3 09-23-2007, 08:20 PM

I think there used to be a big fuse in the box too. On the older cars this is a chunk of metal with holes that some screws go through. After a lot of serious heat cycles it buckles and then begins to fatigue. Eventually it cracks and you don't get juice to the glow plugs. Since the ends are bolted down, it doesn't move when it fails and you may have some difficulty seeing that it is cracked. Jim

777funk · #4 09-23-2007, 08:36 PM

This is doubtful but you may also have a bad wire or two to the Glow Plugs. I've changed glow plugs before and messed up wire ends (they are hard to reach on my 603 engine). Anyways, I'd also check for continuity on your wires. It is after all an 84 car. Wires can wear out. But as the two moderators said, it's most likely something to do with your GP relay. The 80 amp fuse is worth checking, easy to do with an ohm meter. then check voltage at the connector the goes to your GPs it's 4 pins with wires going to the GPs. Just snap the back cover of the wire harness off, turn the key to position two and quickly measure for 12 Volts. Make sure you have the black wire of your meter on a good ground of course.

Ben01 · #5 09-23-2007, 09:31 PM

Thanks for all the replies.

I can't check the plugs at the moment, because the motor is warm again. However, where's the 80 amp fuse you're referring to? If it's the metal strip screwed to the top of the GP timing relay box, I already metered that to be good.

pawoSD · #6 09-23-2007, 09:56 PM

Quote:

Originally Posted by Ben01

Thanks for all the replies.

I can't check the plugs at the moment, because the motor is warm again. However, where's the 80 amp fuse you're referring to? If it's the metal strip screwed to the top of the GP timing relay box, I already metered that to be good.

That would be the fuse...looks like the problem lies elsewhere in the system...

Ben01 · #7 09-24-2007, 01:04 AM

Okay, I metered the GPs themselves when cold and the ignition switched to the no.2 position. No juice.

Brian Carlton · #8 09-24-2007, 08:42 AM

Quote:

Originally Posted by Ben01

Okay, I metered the GPs themselves when cold and the ignition switched to the no.2 position. No juice.

I realize the fuse checked OK with the meter.

Please remove the fuse and look it over carefully outside the box. If it looks original..........replace it. If it's cracked, it won't transmit the current but the meter will find it OK.

If the fuse is not your issue, you're looking for power to the relay on a violet wire from the ignition switch. The wire should have power whenever the ignition switch is turned to the #2 position and the power should disappear when the ignition switch is turned back to the 0 position.

If you find this wire and it switches properly, the relay is confirmed to be NG.

vstech · #9 09-24-2007, 09:14 AM

ok, you have no power at the GP's, but do you have power at the fuse itself?
1. turn off the key.
2. turn the key to the #2 position (do not go all the way to the #3 position, or it will turn off the relay.)
3. quickly get the meter out and measure to ground on both screws of the strip fuse. if you have power on one screw but not the other, the fuse is bad. if you have power on both screws, quickly swing the meter over to one of the GP's. no power there? bad GP relay.

probear · #10 09-24-2007, 09:38 AM

Quote:

Originally Posted by JimSmith

I think there used to be a big fuse in the box too. On the older cars this is a chunk of metal with holes that some screws go through. After a lot of serious heat cycles it buckles and then begins to fatigue. Eventually it cracks and you don't get juice to the glow plugs. Since the ends are bolted down, it doesn't move when it fails and you may have some difficulty seeing that it is cracked. Jim

Exactly what happened to my SDL last week. Yep, at a glance, the fuse looked OK, but closer examination showed it to be broken.

Magoo · #11 09-24-2007, 01:42 PM

Can you hear your relay working? Not sure how a 190 is setup, but mine makes a loud "CLICK" on pickup and dropout.

pawoSD · #12 09-24-2007, 01:44 PM

Quote:

Originally Posted by Magoo

Can you hear your relay working? Not sure how a 190 is setup, but mine makes a loud "CLICK" on pickup and dropout.

Yep, it should click on and off, its pretty loud. If its not clicking either its not getting a signal to activate from the ignition switch or the relay itself is bad.

Ben01 · #13 09-26-2007, 01:48 AM

Okay, more confounding revelations in Mercedes land.

This morning I decided to check the power from the ign lead, so I removed the plug @ the relay and metered it, only to reveal that it had power. It just didn't have power from the prongs leading to the plugs themselves. I plugged everything back in and...it worked. For the first time in two weeks it worked perfectly. And it worked again when I started it up this evening. I'll be damned.

slarson80 · #14 09-26-2007, 02:19 AM

Either the connections where loose and you plugged it back in nice and tight. Or you removed some corrosion just by unplugging and reconnecting. I'd recheck the connections, and clean the contacts with alcohol.