W124 Continuous voltage to glow plugs + ignition vacuum connection

[Olze]

Hey!

I've been lurking and looking around but I can't seem to find a solution to this problem..!

I've 250D N/A (om602.912), and I get continuous voltage to couple of the glow plug relay pins. When you turn on the ignition, there will be the usual 12+ volts to all 5 pins. After about 20secs, the relay shuts off normally and voltage drops to 0 at 3 pins. One pin still has 0.8 volts, and one has 5.8 volts. The voltage to those two pins never disappear, even after driving for an hour or so. It does not matter whether the glow plus wires are connected to the relay or not. But if they are connected, the voltage goes all the way to the glowplug itself.

Also the glowplug light comes on only after the relay shuts off, and then disappears after a while. I've tried another glow-relay. There's no fuses in this particular relay and I can't find no wiring diagrams! Relay = 007 545 99 32

Another problem is that I've changed ignition switch, and the tumbler, and now my car wont start if both of the vacuum lines are connected to the ignition body vacuum hose nipples. The injection pump shut-off lever activates if both of them are connected. I've tried switching the lines around in the nipples. The car starts perfect if another one of the nipples are disconnected. The other nipple sucks air, the other one does nothing. If you put them together, car shuts off. Is there something in the ignition body that I've screwed up? The vacuum lines are ok.

Cheers!
- Olze

 

[grober]

INTERNALS of pattern part -Its a double relay one coil contacter is not switching off

the control electronics are represented by a box with a transistor - they will have inputs/outputs to/ from the following

taken from these pattern parts via part no given
0075459932 - Relay, control unit OE number by EVOBUS, MERCEDES-BENZ, STEYR | Spareto

 

[grober]

Your ignition vacuum switch is not isolating the injection pump shut off vacuum actuator- either its not adjusted correctly or its faultty There are 2 setups
https://www.startekinfo.com/StarTek/outside/11832/Resources/201Create/PDF/70006.pdf

 

[Olze]

Thank you for your replies and help! I really appreciate it.

The relay-diagram seems to be the same even if that one has a fuse in it. It's helpful, thanks. Is it possible there's no fuse at all in the whole system in my case? Or is it possibly controlled by OVP-relay, and if the ovp-fuse would blow out if necessary?

I tried another OVP-relay from a scrap-car I have aswell, because someone told it fixed their similar problem with the GP-relay, but it's not the same relay as the one in my diesel, it's from M111.960 2.2l DOHC gasoline engine (W124 too) - the part numbers don't match and it is 15A instead of 10A. I tried it on anyway but it didn't fix the problem, neither did it cause any more errors. But I'm unsure, maybe a correct OVP-relay could fix the GP-relay problem with the voltage coming to the two pins. I'm bad with electronics, and I'm trying to understand what could cause a problem like this. I'm here stratching my head, but then again I'm willing to learn more, so I'll try my best to figure out the problem by myself rather than paying a shop to fix it.


The pdf. you provided has such a massive amount of useful information. Thank you so much. I'll take a look in to the vacuum system later on! I had to take my ignition body apart and it sort of jammed itself up, I was dumb and turned the axle inside the ignition body, WITHOUT the tumbler being in place, and something jammed, and I had to use force to "flip" the internals back in their correct position, I guess that's the part where something messed up with the vacuum switch - I removed it aswell and put it back in place back then.

 

[grober]

Pin 30 is an "always live" connection direct from the battery- the fuse is that fuseable metal link at the end of the relay base ---pin 15 is live on ignition switch on. the varying voltage on the paired injectors that won't switch off may be indicative that one injector is burned out which might explain the relay failure. Your best bet is to replace the glow plug relay but check the glow plugs are OK first

 

[Olze]

The relays I have haven't got the strip fuse at all - even if it's the compatible part number. That's why I was wondering whether there's a fuse somewhere else. I'll try to get a picture here as an attachment.

The weird thing is, I have tried another relay too, and the same problem persists - even if glow plug wires wouldn't be connected! That's what makes me think the problem can't be in the plugs, even if they were bad. Then again, if the relay needs the glow plugs too, to function properly? The another relay I tested was used, but..could it really be bad aswell, feels like too bad odds but it's possible.

 

[Olze]

-

 

[grober]

Odd results like this are usually down to connectors/wiring/ earthing problems. Assuming the 2nd relay is ok- big assumption if its not fuse protected! - then all thats left are the connectors /glowplugs.

 

[Ted]

My guess fwiw is that the injectors where you are seeing a voltage have gone high resistance. There will be a slight voltage ‘bleed’ which will not be seen on the good injectors as they will be sinking it to earth.
Definitely worth checking the resistance of all injectors and seeing if they are to spec.

 

[Olze]

Hmm..shouldn't the voltage be at zero at the relay itself on all of the 5 pins, after it has "clicked" itself off? I have unplugged the glow plug wires compeletely from the relay, yet it still reads voltage from two of the pins. (Pin G4 = 5.8 volts, pin G2 = 1.8 volts)
If I plug in the glow plug wires, the voltage never changes - but with
multimeter, I tested that the voltage goes all the way to the plug. The relay just never completely shuts off the voltage coming to those two pins. And this happens with both relays, same pins, same voltage. That seems so odd! The glowplugs all read .8 ohms (with my meter), except one, which reads like 750ohms, so that one is most probably shot.

Edit: I want to (eventually) change all the plugs, I just want to make sure there's no continuous voltage coming to the new plugs which'd kill them "prematurely." Would it be possible to remove the wires going to the glowplugs, attach them to the new plugs, and run a ground wire from the body of the new glowplug to a proper ground point, and test them and the relay like that. (New plugs: attach the wires from old plugs to them, run ground wire from body, connect to relay, test if they glow properly - without the plugs being in the engine!)

 

[Ted]

I agree, that is strange if yours is as per the diagrams shown. G2 and G4 should be at the same potential whatever.
5.8 volts into 0.8 ohms should result in a current of 7 amps - around 40 watts. I’d expect the glowplug is getting pretty warm at that. Is there any way of putting your ammeter into circuit just to double check that?

 

[grober]

https://www.startekinfo.com/StarTek/outside/12264/Program/Engine/602_603/15-4000.pdf
FROM
Mercedes-Benz Model 124 Service Manual Library

 

[grober]

https://www.startekinfo.com/StarTek/outside/12264/Program/Engine/602_603/15-0705.pdf
Looks like you have the later relay with the built in electronic over current/short protection??
One "off the wall" suggestion would be that if the relay electronics uses TTL Logic it normally runs at around 5 volts so is this the source of the voltage you are seeing that's seeking a shorted path to earth via a glow plug connection?
First thing to check would be if you have indeed the correct relay for your cars circuitry/wiring via your MB dealer/vin number- they may all work after a fashion . Other might be to check the viability of the earth connection for the electronics is good at both ends - pin 31 on the relay - not sure where the earth connection to the body/engine is for this [ might be behind the dash?] but you could rig one up temporarily?
This may also be usefull altho it refers to the earlier relay design
Mercedes Diesel Glow Plug Repair

 

[grober]

A link to let people know what these relays look like inside
Inside the box: VDO Glow Plug Relay 5 Zyl - PeachParts Mercedes-Benz Forum
its the old design with the fuse link and the circuit board will be different in the newer model but gives an idea.

People have been known to operate these with the can off temporarily to monitor what happens to the main contactors.

 

[grober]

And a picture of the glow / after glow relays showing the big difference in the circuitboard

 

[wiq]

MBUSA ISP Portal
Looks like you have the later relay with the built in electronic over current/short protection??
One "off the wall" suggestion would be that if the relay electronics uses TTL Logic it normally runs at around 5 volts so is this the source of the voltage you are seeing that's seeking a shorted path to earth via a glow plug connection?
First thing to check would be if you have indeed the correct relay for your cars circuitry/wiring via your MB dealer/vin number- they may all work after a fashion . Other might be to check the viability of the earth connection for the electronics is good at both ends - pin 31 on the relay - not sure where the earth connection to the body/engine is for this [ might be behind the dash?] but you could rig one up temporarily?
This may also be usefull altho it refers to the earlier relay design
Mercedes Diesel Glow Plug Repair

First off sorry for this but I really cant seem to find anything else on the internet about this. I have an issue with the glowing part of my car and have the same never realy. How can I check if it has gone off? like the older one had a fuse so you could easily see if it had popped but what about the never one? Also the thing is that I dont own any electronic working tools so I cant check the voltages. I really dont hope my plugs are bad since It is like -18 here rn. Would not want to work that hard out there.

Also a weird thing that happens:
1. turn the key: no glow light
2. Start the car (I have not done this since the glowing failed and then I had a warm engine): The light came on
3. After a while it turned off

What issues do I have and how do I check if the failsafe on the relay has gone off since there is no fuse?