Electrical problems....

[craigieeb]

I'v been working on the m50 trying to find out why cylinder 4 is not playing ball,
but thats not the problem i need help with,

I pulled out the coils to do a compression test, and when i put it back together again, it was refusing to start,
turn the key and the icv was not buzzing, and the pump wasnt priming,
so iv been over everything, to try and diagnose what changed,

I checked, fuses, relays, connections to the dme relay, changed the dme relay for a working one,
(tested on another e30)

but nothing, i then put an earth direct from the body to the brown/earth pin on the underside of the dme relay and it fired straight away,

but once its running, if i take off the earth the engine will cut straight out,
so is that a broken earth somewhere along the wiring?

and i dont know if this is related, but the rev counter has stopped working at the same time,

everything was working a few days ago when the car was out for it's shake down, I drove it off the drive and drove it back on before it refused to start.

anyone got any ideas at all?
I'v exhausted every avenue

[Brianmoooore]

Very strange! The brown wire on the DME relay isn't an 'earth' unfortunately. One end of the DME relay's coil is connected to permanent live (battery +), and the brown wire, from the other end of the coil, is earthed by the ECU, when instructed to do so by applying power to another of the ECUs pins (49) from the ignition switch.
Check that power is reaching here first. If it is, then it could be a failed section of the ECU.

[craigieeb]

Yeah I thought it was a bit strange also,
I'll find out where it connects to on the VEMS ECU and check it.

I hope the ecu hasn't fried it's self