Vito V6 glowplugs not working

[MikeyBee]

The glowplugs are not all working on my W639 V6 Dualiner. This has been an ongoing problem for years. All the glowplugs have been replaced more than once and now I'm down again to just two or three working I reckon judging by the way it just about starts and runs on 3 or 4 in the morning, before picking up onto 6. The garage looking after the van seem perplexed and are suggesting a new engine wiring loom, which I'm reluctant to agree to without a proper technical diagnosis proving where the fault lies.

So I'm trying to learn about how the glowplug system works. On my collection of old vintage diesels (in boats) the glowplugs are simply wired to the 12V supply and turned on with a relay. On my Vito there seems to be a "Glow plug controller" with one big wire and a 12-way multiplug connected into it. What does this do please? Does the 12-way connector carry data or is it the 12V power connections to the glowplugs? Or something else, does anyone know? We've replaced this glow plug controller on the off chance of it helping but the new one made no difference.

Thanks for any advice anyone can offer.

 

[Blobcat]

Modern diesel engines use the glow plugs at many different times to improve combustion - not just at start up. I’d find a Mercedes independent specialist and get them to go through the glow plug controller and diagnose it properly

 

[mattkh]

Please put up some photos of :-
1. The 12way multiplug
2. The glow plug controller
3. The view of any side showing the cables going to the 3 glow plugs
4. The plug connected to any one of the glow plugs
Please make sure that the colours of the individual wires are easily seen.
Thanks

 

[M80]

Glow plugs should last for years.
If you are replacing at regular intervals I suggest they are :
1) cheap plugs,
2) the wrong voltage plugs for the controller (there are 2 types),
3) they were installed with too much torque and have twisted (that should be apparent on removal.

Glow plug controllers are a common failure.

 

[MikeyBee]

Modern diesel engines use the glow plugs at many different times to improve combustion - not just at start up. I’d find a Mercedes independent specialist and get them to go through the glow plug controller and diagnose it properly

Hmmm that's interesting, I didn't realise that. Thanks for the info.

I'm tending towards being inclined to just scrap it and get a lower mileage one as its pushing 300k miles now, and the dual mass flywheel or propshaft makes a horrible booming noise under gentle acceleration. Also the silver bodywork laquer is beginning to delaminate so I think this vehicle needs some big money spending on it to fix all this, and then I've still got a high mileage example probably living on borrowed time.

 

[MikeyBee]

Glow plugs should last for years.
If you are replacing at regular intervals I suggest they are :
1) cheap plugs,
2) the wrong voltage plugs for the controller (there are 2 types),
3) they were installed with too much torque and have twisted (that should be apparent on removal.

Glow plug controllers are a common failure.

That too is interesting. I had all the glowplugs changed at about 200k as two or three had packed up according to the fault diagnosis interrogation and all six were changed as a set IIRC. I thought it odd as the motor still started easily at this stage.

All the new glowplugs failed pretty rapidly. My vehicle bod had fitted NGK glowplugs as Rygor were out of stock of Merc branded plugs at the time and he reckoned NGK were therefore shyte (technical term). A new set of Merc plugs were fitted along with some sort of glowplug lead upgrade kit supplied by Merc as there was a known problem with the connections onto the plugs, and this starting problem has persisted ever since then.

He fitted a new controller a month ago with no change.

I'm not up for taking it to bits and photographing the multiway plug that goes into the controller but I watched it being changed and the wires into the 12-way connector were all concealed inside a single black-wrapped loom cable with a big plug on the end IIRC. I can photo the old controller that came off though, I have it here. Will post some pics shortly.

 

[MikeyBee]

 

[mattkh]

.........I'm not up for taking it to bits and photographing the multiway plug

Thanks for the photos you have pu tup.
I am still without any wiring diagrams. I was hoping to workout the circuit by looking at the colours of the wires.

 

[supernoodle]

I don't know the Vito, but glow controllers are pretty similar in all marques of that era. Plugs used in low cost variants tend to be metal plugs, mid range use low voltage metal and the higher end trend to use ceramic. Metal can be used before start and for a short post glow (after engine has started) . Low voltage before start and a bit longer post glow. Ceramic, before start, much longer post glows.

The glow module is pretty dumb. The ECU decides when and for how long to glow. It will communicate this request to the module using either PWM, LIN or CAN. The module might do some ground offset compensation. The module can also report back error information to the ECU. (In the case of PWM, diagnostic ground keying is used to allow two way communication)

AFAIK Merc tend to use LIN bus glow controller. LIN is a 12v serial data signal.
So that 12 way plug will have the data (LIN), glow module power and ground and output for each plug.

I'm not sure where in the harness the garage is expecting there is a problem. If there is a problem with the data line, ECU would flag an error. If there was an open/short circuit problem with the glow outputs, glow controller would detect this and report back to ECU. If you think plugs are fubar with no errors, that shouldn't happen.
Regardless you can always check module output and plugs with a meter. Even better is to monitor current draw of each plug with current clamp and oscilloscope.