Glow Plug relay is Frying Strip Fuse - Page 2 - PeachParts Mercedes-Benz Forum

Mustang_man298 · #16 11-15-2007, 12:23 AM

Reading your posts, it looks like you keep rushing and leading yourself down a lot of goose chases. Slow down a minute now....The strip fuse you are blowing has one devoted purpose, the single heavy 12v wire that sits in the screw terminal on the relay is battery power for the plugs, that fuse strip sits between that wire and the glow plugs, and power on that circuit only passes thru a normally open contact on the relay that closes when you activate the glow cycle. It has absolutely nothing to do with the relay control circuitry. Your problem is either in the plugs themselves, in the 6 pin harness that goes to the glow plug studs, or internal in the relay, thats it.

Now do this in this order:
Install a correct fuse. Pull the 6 pin glow plug harness from the relay, leave the 4 pin plug alone as it has nothing to do with this problem. turn on the glow cycle, if fuse is good then relay is fine. Next pull all of the wires from the glow plug studs and keep them isolated from touching things. Using a reliable ohmmeter, place a lead on each glow plug wire, and place the other lead into the female pins on the 6 pin connector, you should only read continuity on one pin at a time, which would be the glow wire you're touching with the other lead. Repeat this for each wire. If a wire reads to no pins then it has gone open (which is not your problem however, and will not make the fuse blow). Also inspect the harness for cuts and damage. If it reads out ok then the harness is ok. Wanna double check it now? Make certain the ends are still isolated, plug the harness to the relay and turn it on, if the fuse stays, its good. Lastly read the ohms from each glow plug stud to a good clean spot of metal on the head. I believe you are aiming to be near the 1.1 ohm area. In any case if you made it to checking the plugs, thats where your problem is, and you can connect each plug one by one until the fuse blows (using the correct fuse) and making sure to keep the loose ends isolated on every test. When you find the one that blows the fuse, try hooking it up by itself if you still question it.

Diesel911 · #17 11-16-2007, 12:32 AM

Take a look at this thread. He dose not have a the same problem as you do but he also cannot find what is wrong with his system. The thread leads to the possibility of buypassing your glow plug relay (as a temp fix) so you can get back on the road.

After-glow/GP relay need explanation, please help

I bypassed the glowplug relay on my Volvo diesel and it has worked for me. I left some instructions and a web site where some pics are posted on the above thread. I left a couple post on this thread starting with lucky #13th post.

vstech · #18 11-16-2007, 08:45 AM

#14 can handle 15 to 20 amps without getting hot, you are pulling 60 or more here, #22 maxes out at about 2 amps... get a larger piece of wire, 14 is a nice size fuse, it WILL get hot with that load on it, but it will not melt in 30 seconds. I would put in some 12, it's rated for 20 to 25 amps, and will not get as hot as quickly. #22 phone cord is just WAAAAAYYYY too small for the 60 or so amps that 6 GP's pull.

raslaje · #19 11-16-2007, 01:56 PM

Here's something from 1985 300D 617. Might help, not sure how this will come out as converted from pdf to gif

Please tell me how to post pictures?-glow-circuit_html_6011f520.gif

Please tell me how to post pictures?-glow-circuit_html_6011f520.gif

gmaltz · #20 11-17-2007, 10:26 AM

I have been away for a few days now and thanks for all your help guys on this problem. Well back out in the garage to try all your suggestions. Good thing I have my waste oil heater out there. Temps down to low 30's this morning here in NY.

Just to get to these glow plugs and terminals is such a hassle (603 engine), plus all the wvo plumbing, I might take off the intake manifold again. Its almost impossible to test the GP wiring with it on. OK, back to work.

gmaltz · #21 11-18-2007, 06:45 PM

Quote:

Originally Posted by Mustang_man298

Reading your posts, it looks like you keep rushing and leading yourself down a lot of goose chases. Slow down a minute now....The strip fuse you are blowing has one devoted purpose, the single heavy 12v wire that sits in the screw terminal on the relay is battery power for the plugs, that fuse strip sits between that wire and the glow plugs, and power on that circuit only passes thru a normally open contact on the relay that closes when you activate the glow cycle. It has absolutely nothing to do with the relay control circuitry. Your problem is either in the plugs themselves, in the 6 pin harness that goes to the glow plug studs, or internal in the relay, thats it.

Now do this in this order:
Install a correct fuse. Pull the 6 pin glow plug harness from the relay, leave the 4 pin plug alone as it has nothing to do with this problem. turn on the glow cycle, if fuse is good then relay is fine.

THIS CHECKED - OK

Next pull all of the wires from the glow plug studs and keep them isolated from touching things. Using a reliable ohmmeter, place a lead on each glow plug wire, and place the other lead into the female pins on the 6 pin connector, you should only read continuity on one pin at a time, which would be the glow wire you're touching with the other lead. Repeat this for each wire. If a wire reads to no pins then it has gone open (which is not your problem however, and will not make the fuse blow). Also inspect the harness for cuts and damage. If it reads out ok then the harness is ok.

THIS ALSO CHECKED - OK

Wanna double check it now? Make certain the ends are still isolated, plug the harness to the relay and turn it on, if the fuse stays, its good.

CHECKED - OK

Lastly read the ohms from each glow plug stud to a good clean spot of metal on the head. I believe you are aiming to be near the 1.1 ohm area.

ALL PLUGS ARE NEW BOSCH AND CHECK OK - 0.8 ohms

In any case if you made it to checking the plugs, thats where your problem is, and you can connect each plug one by one until the fuse blows (using the correct fuse) and making sure to keep the loose ends isolated on every test. When you find the one that blows the fuse, try hooking it up by itself if you still question it.

Chris, I am still working on that part now, checking each plug separateley connected however a strange thing is happening.

two plugs are turning on a green light next to the glow light in dash but the rest are not.

WHAT IS THIS GREEN LIGHT? Its not in the operating manual and I can not remember if it is normal or not!

gmaltz · #22 11-18-2007, 09:15 PM

OK - Huge progress being made now!

Please disregard the previous post abut the green dash light. My mistake - Duh. When checked the black wire for continuity of the dash bulb, I put the bulb back in the wrong hole. So the glow bulb was lighting up green instead of yellow.

Any way all the leads checked out good and all plugs are good. Also took the cover off the relay and verified the contacts closing on each glow plug circuit individually with key to position 2 while all other leads disconnected and insulated.

I am now getting a dash glow light finally and will have to reinstall the intake manifold and wvo plumbing before engine start.

Upgraded temporary home made stripfuse to 18 ga solid copper (which work OK) until aluminum flat fuses arrive. The previous 22 ga fuses kept blowing and hampered testing.

gmaltz · #23 11-18-2007, 09:37 PM

The only way to easily get at the plugs and wires on this motor is to yank the intake!

To only way to really verify that the relay is working is to remove the cover as watch the contacts close when the circuit is energised.

gmaltz · #24 11-19-2007, 12:12 PM

SUCCESS!!!!!!!!!!

Reinstalled the intake and buttoned everything else up and she fired right up! WOW. I am so relieved. Still not sure exactly what was causing the short, but I am assuming it was one of the glow plugs. The wiring was OK and I even checked the old relay with out the cover on it and it was closing ok when the glow cycle was initiated so now its a spare in my shop.

Now some more suspension adjustments and back in service!

unkl300d · #25 12-29-2007, 02:47 PM

Gerry, glad to hear you resolved your problem. I just had to twice return new Bosch glow plugs (india) due to failed resistance tests.
I am now awaiting replacement Beru plugs, hopefully better quality production.

gmaltz · #26 12-30-2007, 07:12 PM

Thanks Curry. My 300D Turbo has been running good now for over a month now so my Bosch plugs seem to be OK for now.

Still have another issue I'm dealing with though. Rear end clunk!

I replaced most of the rear bushings including the sub frame bushes and control arms too to no avail.

It might be the axle shafts clunking due to wear, not sure.

Diesel911 · #27 12-30-2007, 11:32 PM

Quote:

Originally Posted by Diesel911

Take a look at this thread. He dose not have a the same problem as you do but he also cannot find what is wrong with his system. The thread leads to the possibility of buypassing your glow plug relay (as a temp fix) so you can get back on the road.

After-glow/GP relay need explanation, please help

I bypassed the glowplug relay on my Volvo diesel and it has worked for me. I left some instructions and a web site where some pics are posted on the above thread. I left a couple post on this thread starting with lucky #13th post.

That is my post mentioned here is the wireing drawing I made for another post. Also when I tested 1 glow plug with an amp meter connected the plug drew 30 amps for a second or 2 and setteled down to 16 amps steady. Your wires should be able to handle 30 amps. If I remember correctly I used 10 guage wire. ALso there is no fuse in my system; one should be added between the battery and the solenoid

gmaltz · #28 01-01-2008, 03:15 PM

Thanks Diesel/911.

My system is up and running fine now. Replaced the temp 18 gauge strip fuse with new factory aluminum ones. The copper temps worked ok for about a week though until new ones arrived. She starts fine and the new relay was probably not needed since I believe the culprit was one or two of the glow plugs were shorting. Replaced all of them with new Bosch units and all back together.

This was a great learning experience for me and as always many thanks to you all on this great forum.