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Discussion Starter #1
Hi Folks,

I'll cut straight to the chase on this one as I've been through a lot of diagnostics to solve my problem.

Basically, my glow plugs are not heating and the old shed is having starting issues. Having dived into the Ebox (under the hood) and found the glowplug relay there is a damn big red cable that is attached to the relay (12v 100A I think) however, when at rest this cable has 2.5 volts when at key pos 2 it drops to 0 volts. I suspect that there is something a little wrong here, but before I shell out on a new relay does anyone know what power should on this fat red cable and when? The relay does click when activated but what I do not understand is why is there only one red cable going to the relay, I thought it it were switching there should be at least two!

Any experts out there that can point me in the right direction?
 

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Discussion Starter #2
Fixed - Well very nearly...

So the process goes like this.. the big red wire supplies 12v (and a lot of amps) to the glow-plug relay in the EBox - the glow-plug relay in turn supplies this power to each of the glow-plugs (the switching of the relay is controlled by the ECU depending on the engine block temperature.

I found the 100A fuse (eventually), it's buried in the main fuse board behind the glove box and it is not a blade fuse, but a proprietary BMW fuse (61138364631). Easiest way to get at it is to 'un-hook' the fuse board so that you can get at the top-panel, unclip it and you'll find a bank of hi-ampage fuses. Be careful with those metal objects chaps, there are some big bus-bars in there.

So what caused the fuse to go pop? No4 Glow-Plug had taken a turn for the worse in a previous life. I pulled the power from No4, applied a fused bridge to the relay and the little beggar started perfectly.

Now it remains to get a fuse from BMW of Tuesday and that should be it! DONE!
 

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My fuse keeps on blowing

Hi there,

I know its been some time since this thread was alive, but anyhow, here I go...

I have a 320d Touring, M47 (136bhp). I happen to have starting problems when cold, so I started measuring on the plugs, supply voltage and so on.
I have measured the glow plugs directly on the engine and read each approx 0.6 ohm, which seems to be OK. When I measure on the disconnected relay connector, I read more or less the same.
I measured on the relay input 1,54 volts. I figured the 100 amps fuse must be bad so I replaced the fuse and measured 12,5 volts on the relay input afterwards. Way to go I thought...
After starting a couple of times, I measured again because the engine still wouldn't start. I measured 4,5 volts. Fuse blown again?! The fuse seems to act like a resistor, since I measure 4.5 volts on the relay input.

So I figured somehow the current must have been greater than 100 amps! Then I disconnected the big supply wire and measured 0.2 ohms between the relay input and ground (Ignition turned on).
This would mean, assuming the battery voltage is 12 volts, 80 amps of current would flow. Even 14 volts would raise the current only till 93.3 amps. While glowing, the resistance should increase and the current should therefore go down.
So I'm puzzled now. Measuring between the disconnected thick supply wire and ground (also removed the fuse) didn't show any short circuit (infinite resistance).

Does anybody have an idea?

Regards,
Marvin
 
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