Glow Plug Problem! - PeachParts Mercedes-Benz Forum

#1 01-05-2004, 08:58 PM

I just got an 87 300 TD wagon, The prior owner changed all the glow plugs one year ago. The other day the car would not start and the glow Plug light would not come on, the Relay fuse was burnt, so i put in a new fuse and it burnt out immediately. So I ordered a new relay from MB-but I am wondering if it is a good idea to change the glow plugs also? how ofton should they be changed?
I also have one other concern: I am a Ham radio enthusiest, and I hooked up my 11 amp radio into a cigarette lighter adapter, and THAT is exactly when i noticed the problem began. I asked a mechanic who said it is unrelated because the cig lighter is a different line, but just wondering

Fisherman · #2 01-05-2004, 10:24 PM

One thing you might find though is that your wipers run when you transmit. I found this on my 300 with my CB plugged into the cig lighter. Too weird.

Test the GPs with a ohm meter. I belive they should run around .06 ohms but i have had them at .05 also and worked fine.

The relay could be it but there is a troubleshooting section on the relay on the CD for this car. You might try going that route or checking a wrecker as they are kind of spendy I think.

You can find the reapir manuals on CD on ebay a lot of the time.

P.E.Haiges · #3 01-05-2004, 10:42 PM

Kobeck,

I would think you have one GP with a dead short. Check the GP with an Ohmeter and look for the one with much lower resistance than the others. You will need a digital Ohmmeter to do this.

I you don't have an ohmeter, you might disconnect all the GP wires except one and energize the GP one at a time to see if one blows the fuse. If one blows the fuse, that's the bad one. However, this might not work because without the other GP working, there might not be enough current drawn by the shorted GP alone to blow the fuse.

Use this test if the above test does not work: Disconnect one GP and energize the GP. Repeat this procedure until the fuse doesn't blow. That then is the shorted GP. You will need about 5 extea fuses but they are inexpensive.

The test below is the ultimate test but you must remove the GP to perform the test: Remove the GP one at a time and connect them directly across the battery terminals using 2 Vice Grip pliers. The one that draws a lot of current (large spark when connected) and doesn't glow, is the shorted plug. Be careful, the GP get very hot.

Cancel the order for the new GP relay. When you find the shorted GP, you won't need it.

I don't believe the problem is related to the Ham radio in the lighter socket either. 11 amps might less than the lighter draws and its a separate circuit.

P E H

#4 01-06-2004, 12:59 AM

Quote:

Originally posted by P.E.Haiges
Kobeck,

I would think you have one GP with a dead short. Check the GP with an Ohmeter and look for the one with much lower resistance than the others. You will need a digital Ohmmeter to do this.

I you don't have an ohmeter, you might disconnect all the GP wires except one and energize the GP one at a time to see if one blows the fuse. If one blows the fuse, that's the bad one. However, this might not work because without the other GP working, there might not be enough current drawn by the shorted GP alone to blow the fuse.

Use this test if the above test does not work: Disconnect one GP and energize the GP. Repeat this procedure until the fuse doesn't blow. That then is the shorted GP. You will need about 5 extea fuses but they are inexpensive.

The test below is the ultimate test but you must remove the GP to perform the test: Remove the GP one at a time and connect them directly across the battery terminals using 2 Vice Grip pliers. The one that draws a lot of current (large spark when connected) and doesn't glow, is the shorted plug. Be careful, the GP get very hot.

Cancel the order for the new GP relay. When you find the shorted GP, you won't need it.

I don't believe the problem is related to the Ham radio in the lighter socket either. 11 amps might less than the lighter draws and its a separate circuit.

P E H

Hi PE H
When I blew the fuse, in order to start the car my buddy used the screw drive to arc the current in place of the burnt fuse, so if one GP is bad would the thing have still worked?
I think as a precaution I am just going to change ALL the GPs anyway, they are cheap enough, rather than try to find out which one is the culprit....I dont have the tools or patience to do it my self so I guess I will have to take it into the service station tomorrow anyway. I can pop the new relay in though, but I am wondering what i should now do, because if it is a shorted plug, than the new relay will just blow the fuse immediately anyway and i wanted $180.00 for a relay, but the car is sitting in my driveway disabled so i am in a pince

Tell me, how hard and what what tools would i need to do the plugs myself????

P.E.Haiges · #5 01-06-2004, 12:39 PM

Kobeck,

Sorry,

I'm not familiar with removing the GP on an '87 engine even though I have an '87 300SDL. I am familiar with R&R the GP on the older 4 and 5 cylinder engines but it looks like the new engines are more difficult to do the GP. Maybe someone else can help you.

If the engine started by the screw driver method, the good GP worked and the engine started. This shows that your old GP relay is OK. The new GP relay will probably blow the fuse the same way. That's why the fuse is there, so you don't melt the wires from having a shorted GP. Can you return the new relay you bought because I'm sure you old one is OK? Don't install it or you might not be able to return it. You should have asked here before you ordered it.

You can do the test I explained about connecting the GP across the battery with no other tools than 2 Vise Grip pliers or equilvalent tools. Even a set of jumper cables would allow you to check the GP this way.

Maybe you are in a higher tax bracket than I am but $60 for new set of GP when only one is needed is too costly for me. I just replace the bad GP. If you replace all the GP, keep the good old ones for spares, you probably will eventually need them.

P E H

HGV · #6 01-06-2004, 01:59 PM

Removing the glow plugs can be a big job or it can be ease depending on a couple of things. The GP's have a tendenacy to cake up with carbon and they can be diffiuclt if they are stuck. If not it is fairly straight forward.

Not sure if you have to remove the intake manifold. According to the namual, you don't. The manual state the following two steps.
1.Cable to glow plugs ...........Disconnect
2.Pencil type glow plugs........Remove, intall.

To easy to be true. If you tackle this your self, soke the glow plugs the night before with penetrating oil to loosen and make it easy. Use a 3/8 drive socket with a universal or ball joint. Go easy and do not strip the head. If one won't budge, don't strip the GP head. Not sure what you may need to remove.

Good luck

Henry

#7 01-06-2004, 02:42 PM

Quote:

Originally posted by HGV
Removing the glow plugs can be a big job or it can be ease depending on a couple of things. The GP's have a tendenacy to cake up with carbon and they can be diffiuclt if they are stuck. If not it is fairly straight forward.

Not sure if you have to remove the intake manifold. According to the namual, you don't. The manual state the following two steps.
1.Cable to glow plugs ...........Disconnect
2.Pencil type glow plugs........Remove, intall.

To easy to be true. If you tackle this your self, soke the glow plugs the night before with penetrating oil to loosen and make it easy. Use a 3/8 drive socket with a universal or ball joint. Go easy and do not strip the head. If one won't budge, don't strip the GP head. Not sure what you may need to remove.

Good luck

Henry

I dont mean to sound dumb, but where exactly are the GPs located? I see 2 wired going into each cylinder, is that them?

HGV · #8 01-06-2004, 04:56 PM

THe glow plugs are not easy to access. The attached section is from the MBZ manual.

Good luck
henry

P.E.Haiges · #9 01-07-2004, 12:38 AM

Dieseldiehard,

BUT a bad GP isn't an "off the air" situation.

P E H

P.E.Haiges · #10 01-07-2004, 10:21 PM

DDH,

I haven't tried any GP replacement on my 300SDL as none of them have failed yet. But I suppose if the intake manifold has to be removed to replace any of the GP, I might replace more than the bad one.

P E H

Tymbrymi · #11 01-07-2004, 10:46 PM

Quote:

Originally posted by kobeck
Hi PE H
When I blew the fuse, in order to start the car my buddy used the screw drive to arc the current in place of the burnt fuse, so if one GP is bad would the thing have still worked?

How long was the screwdriver used as the fuse(seconds/entire glow cycle/etc)? You smell any burnt plastic afterwords? If one of the glow plugs was indeed shorted (sounds reasonable) you just ran a LOT of juice through that GP wire and the relay. That could have fried your old relay, and some wiring, or maybe not.... but I would investigate.

----
John Robbins
'79 300SD

lrg · #12 01-08-2004, 12:54 AM

You'll need a gasket for both sides (ends?) of the manifold, where it attaches to the head and where it attaches to the crossover pipe. While you are at it you should replace the plastic clips that hold the injection pipes to the manifold. You'll probably break most of them taking it apart and it's not unheard off for the injection pipes to wear through the sides if they are allowed to vibrate due to them not being clipped down.

PEH: 4 out of 6 of the 603 engine glow plugs are virtually unreachable without removing the intake. This may be one time where it pays to at least replace all of those 4.

HGV · #13 01-08-2004, 11:27 AM

If you are going to tackle removing the intake manifold, one tool that is indispensable is a tee handled allen with a ball end. The ball end allows for the allen to grap the bolt at a very high offset angle. The allen needs to be about 8" long to work. Also, upon replacing the manifold, make sure that the intake manifold gasket is placed properly before you start tighting the bolts. When I did mind, it wasn't until I got to the last set of bolts that I realized that I missed the alignment.. Had to take the dam thing off again to correct.

Henry