glow plugs circuitry

simion

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Your Mercedes
Sprinter 312 D
Hello and thanks to you all for a very informative forum. Have searched and found some help but could do with some specific questions answering.
I have a sprinter 312 D
Glow plug light is coming back on indicating a fault.
4 out of 5 plug leads have 12V come on for 30 seconds. The 5th plug (nearest the driver) shows no volts and also I can't change it, no room to move the socket. Have changed the other 4 plugs.
The 5 plug wires seem to dissapear into the loom.
Q1: where is the control relay for the plugs.
Q2: is the time that the plugs are on for automatically adjusted according to engine temperature?, 30 seconds seems a bit long to me.
Q3: is the glow lamp controlled by the same relays that control the plugs.
Q4: are there 5 seperate relays, 1 for each plug?
Q5: am I going to have to remove the metal box held on with a torx screw (not sure what it is) to gain access to the 5th heater pug, or should I go to a garage where they may have a special tool.

If I get these answered then I'm well on the way to fixing. Thanks for any help.

Sim.
 

Bolide

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www.w124.co.uk
Your Mercedes
BMW 525 Diesel Touring
Try metering the plugs. You've checked for volts from the glow plug relay, now check the resistance of the glow plugs. I would expect they'll all be about 0.7 Ohm apart from the one where there is no voltage from the relay - I'd expect that to be a short circuit (0 Ohm)

I can't help with the location of the glow plug relay. It will normally have fusible links which melt if they detect a dead short. This might explain the output with no voltage

The duration the plugs are on for is ECU controlled on later Mercedes and is designed to bring the engine up to operating temperature as fast as possible to reduce emissions

Nick Froome
www.w124.co.uk
 
A

andy@pcd-ltd

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What are the first 6 numbers of the chassis number and i will have a look for you
 

brianbrian

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cockney in the West Country
Your Mercedes
w124 250D, SL129-deisel
30 seconds, Far to long for glow plugs to warm up, 8 seconds more like it, and only 1 relay. Hope this helps
 
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simion

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Sprinter 312 D
  • Thread Starter
  • Thread starter
  • #7
Thanks for all replies.
The 5th plug (the one I can't get out because it's inaccessible) is open circuit. Infinite ohms, as opposed to the others which are very low resistance.
The VIN (from the plate by drivers door) has 1st 6 numbers 903412.
Yes I thought 30 seconds is too long. I think I'm being optimistic thinking that changing that 5th plug will help reduce this to 8 seconds. I think this is a seperate issue but I've no idea how to start dealing with it. Where is the timer that determines the glow plug on time? It's a 1996 model so I'll assume the on time is not set by engine temperature (or is it?).

Sim.
 

brianbrian

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cockney in the West Country
Your Mercedes
w124 250D, SL129-deisel
The timer for the glow plugs is in the relay, this could be faulty, so when you turn your ignition on, count 1to8 then try starting it. Hope this helps let us all know
 


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