Ignition Coil Wires - Continuity with Ground with Fuse #10 Inserted

[jrobie79]

So I've been trying to diagnose my no start issue on my m42 (e36 m42 installed into e30). I initially thought it was the CPS, swapped that out, no dice.

While diagnosing and checking continuity between the different components (DME, Coils, Switch, Fuel Pump, CPS's, etc...) I noticed that the Green wire  to ground for all 4 ignition coils only read 7Ω.

I started tracing wires to discover if there was any spots where the wire insulation was worn and/or cut that would indicate near continuity between ground and the green ignition coil wire.

What I figured out was that this wire leads back to pin 7 in the C101. so I unplugged that. The body side of C101 read open from green wire to ground, so that was eliminated. Then I disconnected the ignition switch plug and read that, open, eliminated that section.

What I discovered was that if Fuse #10 was plugged in I was getting the 7Ω reading, if I took fuse #10 out, the Ω jumped to 300+.

Kind of stuck where to go from here, I dug through all the wiring diagrams, but I'm still have trouble where to go from here.

Any advice?

I put all the pictures of wiring diagrams from the ETM that include fuse #10 below:

[DesktopDave]

I'd suspect the transistors are tricking your DMM. I'm not an expert, but I've heard that the DMM essentially powers up the coil driver (forward bias) and then the DMM deduces an incorrect reading.

I'm honestly not sure why #10 would cause any change either. The fuse is only powered in start & run.

I'm not sure about resistance tests with a DMM, but continuity tests often use fairly high voltages. I'm reluctant to use either one, because I wasted an E34 cluster readout once when I hadn't changed a DMM setting. I'd advise against using any continuity tests across any sort of control electronics in BMWs. You never know what kind of control circuit they've designed. Everything built after the E30 has an awful lot of solid-state controllers. I've heard some DMMs will push 9VDC. That's a fatally high voltage for transistors and ICs! It's easy to damage solid state components with that sort of voltage.