'79 240D - where is GP relay? - PeachParts Mercedes-Benz Forum

mbzr4ever · #1 10-22-2007, 06:10 PM

I just replaced all the glow plugs in my resto '79 240D w123, as in my thread:

No glow plug light

and she was running great until this AM.

Put the key in, radio and all lights were going fine, GP light included, then the GP light went off, I went to crank, then nothing. Tried again, nothing, no lights...felt like the battery was dead. But then I got a faint buzzer of like when you leave the lights on, or the key in the ignition - that reminder buzz.

Checked the battery, I'm getting a reading on the multimeter, but nothing to the black fuse (metal strip) box against the firewall.

Question, how do I check the exact voltage on the multimeter for the battery to make sure it is high enough?

Under my dash, I have 2 black boxes, 2 silver boxes. One black box is fastened underneath, about center, and looks like the wires are going to the steering wheel.

Another black box is to the left, kinda hangs around where the parking brake is located. (Maybe it should be attached and out of the way?)

Is this the GP relay? I'd like to test the right box.

Or could this problem be related to the ignition mechanism? It's as if I'm not getting any electrical connection at the switch?

Thanks all for educating this novice, who knows enough to be dangerous...

C.Doner · #2 10-23-2007, 03:44 AM

I believe it is on the steering column under the dash. Probably silver. you could also try a jumper wire over to the fuse. see if that gets it running. easy to find a replacement relay at a boneyard. the 300d 77-79 are the same also. might as well switch over to the pencil style plugs as well.

nuclearw · #3 10-23-2007, 09:44 AM

Funny this happened to my '77 240d as well.. Got it started by cranking thursday, but the master cylinder went out on my way home from work .. rather unpleasent.

2 Days ago I checked, the GP light came on, and the car fired up nice. Last night I changed out the MC, wanted to go take it for a test run but again the GP's wouldnt kick on.

Is there something I should check that would cause an intermittent GP failure, or is it pretty much limited to a bad relay?

Fuse is solid from what I can see, I do have the older loop style plugs. Anyone have a good source, or a part # for pencil plugs that have the right fit?

Stevo · #4 10-23-2007, 10:25 AM

Quote:

Originally Posted by nuclearw

Funny this happened to my '77 240d as well.. Got it started by cranking thursday, but the master cylinder went out on my way home from work .. rather unpleasent.

2 Days ago I checked, the GP light came on, and the car fired up nice. Last night I changed out the MC, wanted to go take it for a test run but again the GP's wouldnt kick on.

Is there something I should check that would cause an intermittent GP failure, or is it pretty much limited to a bad relay?

Fuse is solid from what I can see, I do have the older loop style plugs. Anyone have a good source, or a part # for pencil plugs that have the right fit?

You prolly should start a new thread instead of hijacking this one and its a good idea to ID your car in your signature.

trouble with those loopers is "one goes, they all go". Phil here in the parts dept can help you and their prices are right. The new style GPs are a huge improvement.

nuclearw · #5 10-23-2007, 10:54 AM

Quote:

Originally Posted by Stevo

You prolly should start a new thread instead of hijacking this one and its a good idea to ID your car in your signature.

trouble with those loopers is "one goes, they all go". Phil here in the parts dept can help you and their prices are right. The new style GPs are a huge improvement.

Sorry, added sig after i posted that, and on-topic, which silver box under the dash is the gp relay, the one closest to me?

Stevo · #6 10-23-2007, 11:14 AM

Quote:

Originally Posted by nuclearw

Sorry, added sig after i posted that, and on-topic, which silver box under the dash is the gp relay, the one closest to me?

As I remember the relay is under the driver side 'knee" panel too the left of the steering column.

There is a 50 amp strip fuse on the firewall that often looks good but is not.

79-240d-project · #7 10-23-2007, 11:38 AM

Yup, under the dash.

Double check that 50 amp fuse on the firewall. When I got my 240 I checked mine and it was an 80 amp. The 79 240D has a serial loop type glow plug and the correct fuse is the 50 amp. The 80 amp is for the later pencil type glow plugs.

nuclearw · #8 10-23-2007, 12:54 PM

I just went out and tested it. I didn't realize my multimeter was in the car .. i'll pull the fuse out later today and see what its status is, read 0-ohms.

I'm wondering if plug #1 is dead, I checked the resistance for the plugs, 4,3,2 were .5-.6 1 read what seemed to be in the 300 range(ie the cheap meter saying i cant see me).

mbzr4ever · #9 10-23-2007, 04:08 PM

So the relay is a silver box? I was looking at the black ones....

nuclearw · #10 10-23-2007, 04:12 PM

I think someone said it was black in 81+. On mine the relay is in the cabin, not the engine compartment. I think the same goes for yours, you need to pull the panel from under your steering wheel to access it.

mbzr4ever · #11 10-23-2007, 04:17 PM

Quote:

Originally Posted by C.Doner

I believe it is on the steering column under the dash. Probably silver. you could also try a jumper wire over to the fuse. see if that gets it running. easy to find a replacement relay at a boneyard. the 300d 77-79 are the same also. might as well switch over to the pencil style plugs as well.

Are you saying take a jumper wire from the battery to the fuse?

I wish there were some boneyards around....I live in a pretty isolated area, I think the closest yard is about 90 miles, and the pickings would be slim to find a similar car (I live on the Big Island).

Pencil style plugs - yes, I saw those, but it was longer to order and wait, and I needed to get the plugs right away, so I got the regular loop kind, bosch brand.

I'm still thinking it is a problem in the ignition mechanism, because I'm not getting any lights on the dash when I turn the key.

mbzr4ever · #12 10-23-2007, 04:26 PM

Quote:

Originally Posted by nuclearw

I think someone said it was black in 81+. On mine the relay is in the cabin, not the engine compartment. I think the same goes for yours, you need to pull the panel from under your steering wheel to access it.

yes, nuclearw, I have the panel underneath the steering wheel off, and there are least 2 silver boxes and 2 black ones staring at me.

mbzr4ever · #13 10-24-2007, 04:58 AM

I need to get new reading glasses, this from my previous thread:

No glow plug light

mbzr4ever · #14 10-30-2007, 08:06 PM

Well, this is sooo strange...

After a week of disconnecting the battery and just letting it sit, I re-connected the battery - headlights came on. I turned the key, now all the lights on the panel are normal, even the glow plug. So, I go ahead and start it, it runs!

I just don't get it...let it run for about a half an hour just to charge to battery.

Don't know if I want to take it off my property yet, until I know why it would not start before. I might have to tow it should it not start and I am stranded somewhere.

nuclearw · #15 10-30-2007, 10:55 PM

mbz,

I just replaced the GP on my car.. Unfortunately this is my daily driver, it's been in the 30-40 range at night. I have plugged in the block heater, then letting it crank for 30-60 seconds would start it up...

Coming home was a little harder, ambient temp of 50-60, cranking for 1-2minutes would start it up.

I was in a pinch the other evening to get home when I thought to try this.. After a bit here I found someone else mentioning doing it.

My thought process: compression heats the fuel, it must heat the cylinder.. Eventually it will heat it enough to auto-ignite. This will work if your in a pinch.

Also after your car's engine is warm, you don't even need to run the GP's

Hope this helps