87 190D glow plug fuse? - PeachParts Mercedes-Benz Forum

Doc Brown · #1 09-04-2018, 08:15 AM

Hi 'ya folks,

This weekend I replaced the glow plugs on my OM602. While I had the plugs out, I ran a reamer through the glow plug cavitys.

Anyway before I installed the new plugs, I cranked the engine over to blow out any carbon that may have dropped into the cylinder.

Now that the car is back together, I do not get 12V at the glow plugs, however the glow plug light on the dash continues to work as expected.

When I had the plugs out and cranked the engine over to blow out the carbon, I guess it is possible one or more of the glow plug wires may have come in contact with the engine block.

I found a schematic of the glow plug circuit on the net but there doesn't seem to be a fuse on the high current feed.

Is there a fuse in the glow plug circuit?

Diesel911 · #2 09-04-2018, 10:16 AM

This is glow plug relays that are under the hood.

I am not specifically sure on your year and model. A small number of the newer then 1985's have a circuit breaker built into the glow plug relay. I don't know if there is a removable plastic cover on or not but you will have a button if it has the circuit breaker.

I think the others have as in mine a strip fuse in the glow plug relay. You need to remove the cover to see it.

On my year and model there is no fuse to the main power wire that goes to the Relay until it is inside of the Relay and that wire connects eventually direct to the Battery and is live all of the time.

People have had the strip fuse screws come loose and also the strip fuse can crack as in the picture. If your fuse is cracked you can bridge the fuse with an alligator cip and still retain the fuse protection while you obtain another fuse.
Of course if it is burned you need a new strip fuse.

On mine the strip fuse is 80 amps. I have no picture of the relay with a circuit breaker.

The pictures are of the relay on my year and model.

Diseasel300 · #3 09-04-2018, 10:50 AM

The circuit breaker came along in the 90s with the updated OM603 and OM602's. The 80s cars have the strip fuse unless the glow plug relay has been replaced with an aftermarket or later model version.

Doc Brown · #4 09-04-2018, 02:42 PM

Thanks for the response!. I'm at the office right now and will update my findings as soon as I get home.

Doc Brown · #5 09-04-2018, 06:00 PM

OK, so I found the Glow Plug relay. Mine does not have a fusable link like what was shown above.

I checked the main power wire and it had 12V. Awesome! Next I opened up the GP relay and to my surprise there was no internal fuse. I reckon this relay assembly must be able to sense the current draw or something. Anyway I flipped the ignition key on and I saw the contacts close for about half a second and then open. Crap.

Next I pulled the intake manifold and disconnected all the glow plugs... then flipped the ignition key and the relay closed and stayed closed.....

At this point I'm thinking the new glow plugs are drawing too much current...

GP relay assembly

Glow plugs. Old on left and new on right.

After zeroing the meter, I measures an average of .5 OHMs on the new glow plugs and .8 OHMs on the old plugs.

__E__
I | R

Current = 12.50/ .5 = 25 amps per plug for the new glow plugs..

The old glow plugs calculate to 15.25 amps per plug.

The part number of the old glow plugs is DRX0068 (not Bosch)
The part number of the new glow plugs are 0 250 201 055 (Bosch)

I'm actually sick as a dog with a sinus infection and this concludes todays activities. Any thoughts from the experts?

Doc Brown · #6 09-04-2018, 06:29 PM

Update, The Bosch 0 250 201 055 GP I purchased are the wrong ones for my 87 OM602

I guess I'll put the old ones back in for now.

Diesel911 · #7 09-05-2018, 08:11 PM

Quote:

Originally Posted by Doc Brown

OK, so I found the Glow Plug relay. Mine does not have a fusable link like what was shown above.

I checked the main power wire and it had 12V. Awesome! Next I opened up the GP relay and to my surprise there was no internal fuse. I reckon this relay assembly must be able to sense the current draw or something. Anyway I flipped the ignition key on and I saw the contacts close for about half a second and then open. Crap.

Next I pulled the intake manifold and disconnected all the glow plugs... then flipped the ignition key and the relay closed and stayed closed.....

At this point I'm thinking the new glow plugs are drawing too much current...

GP relay assembly

Glow plugs. Old on left and new on right.

After zeroing the meter, I measures an average of .5 OHMs on the new glow plugs and .8 OHMs on the old plugs.

__E__
I | R

Current = 12.50/ .5 = 25 amps per plug for the new glow plugs..

The old glow plugs calculate to 15.25 amps per plug.

The part number of the old glow plugs is DRX0068 (not Bosch)
The part number of the new glow plugs are 0 250 201 055 (Bosch)

I'm actually sick as a dog with a sinus infection and this concludes todays activities. Any thoughts from the experts?

I hope the member that told me the tip of the glow plugs don't swell up views the pic of the old and new glow plugs. Autolite and sometimes Monark glow plugs sometime swell like that when the fail. Don't use either.

Never read of the pencil type glow plugs coming out of the box with a short circuit. When there is a short circuit it is usually the wires worn thought somewhere.

On my year and model I connected one plug at a time to an automotive dash board type ammeter. 60 was the max amps on the gauge.

When I tested each plug the gauge would peg out at 60amps and then as the glow plug got hotter quickly dropped down and held to approximately 16 amps.

Also the Battery voltage drops when you apply the Glow Plugs to around 11 volts if you battery is good.

Doc Brown · #8 09-07-2018, 05:18 PM

I ended up putting the old glow plugs back in for the moment. While the old GP seem to measure ok, I'm getting poor performance on start up. I reckon the car is hitting on 3 or four cylinders for the first 20-30 seconds.

The new glow plugs that I attempted to install were apparently the wrong ones for my application.

Diseasel300 · #9 09-07-2018, 06:24 PM

A 60x engine with good compression should start even without glow plugs in above-freezing temps. If it's taking that long to hit on all cylinders, you probably have air ingress, not glow plug issues.

Doc Brown · #10 09-10-2018, 06:16 AM

Thats is interesting.... This engine will not start warm or cold without the aid of the glow plugs.

Diseasel300 · #11 09-10-2018, 10:55 AM

Time for a compression test. If the compression is good, it's almost certainly air in the fuel system. Install a piece of clear tubing for your return line back to the fuel tank. It should be full of fuel with no air or foam at all times. If you see air bubbles, foam, or a bubble after sitting, you have work to do.

Doc Brown · #12 09-10-2018, 12:56 PM

Looks like Harbor freight sells an affordable compression tester kit. Any reason I shouldn't pick one up?

For the clear tubing on the return line, I'm thinking of using clear vinyl tubing that can be sourced locally for a few bucks. I understand this is temporary and the tubing will be used just long enough to verify whether or not air is in the system.