I have posted this question also in another thread, but I figured this one is slightly different so 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?