I had some engine trouble on my '94 325is IT car (dropped valve, piston damage, ventilated block, spark plug pushed up out of the head, etc). Since that motor was obviously less than healthy I swapped it out for a used motor out of a '95. I did the obvious maint moves with the engine out (seals, oil pump nut, new knock sensors, crank position sensor, injectors, plugs, etc) and threw it back in the car. It turns over, but no start. The plugs are all dry, but there is fuel pressure. I checked the wiring diagrams and noticed the injector harness was listed as being different for the '95 vs. the '94, so I swapped the harnesses. No change. The ECU is returning just one code for "control unit supply". Googling seems to indicate that it's likely either low battery voltage or a bad ECU. The battery voltage is about 12.5v and the pins on the harness that are supposed to deliver voltage to the ECU read proper voltage. There's also good continuity to ground on both ECU ground pins.

I haven't checked to see if there's spark since I've swapped harnesses simply because there's no easy way to do it with coil-on-plug -- at least not without help. The only thing I could think of is to remove the coil, put a plug in, and ground to the block with a screwdriver and crank to observe spark. Not a viable one-man job, unfortunately. All six coils read proper impedence and there's power at the proper pins in all the connectors.

I mentioned the previous motor destruction event: is it possible that when something metal came up and hammered the end of the spark plug in #6, it shorted the coil and fried the ECU? Is that plausible? Any suggestions for next troubleshooting step? Attempt to locate another ECU? Or just light the whole thing on fire and take up stamp collecting?

Thanks for the help -- I can't put an SIR on it unless I get it running! :P

tom