What would cause an ECU to go bad?

[cj]

My M5 would'nt start this afternoon. I had fuel and no spark. I switched out the ECU with my spare one that has a stock chip and it fired right up.

Cris

[Skeen]

Sometimes vibration will cause some of the soldered joints to crack, making poor connections.

[Rich Euro M5]

My M5 would'nt start this afternoon. I had fuel and no spark. I switched out the ECU with my spare one that has a stock chip and it fired right up.

Cris

Possibly a defective output transistor for the ignition side. I haven't seen recommendations for what type of transistor to use. I do know that you WILL NOT find a cross reference for the transistors used in the ECU. Maybe someone will chime in with a transistor PN that will work.

Rich

[cj]

The weirdness continues. I went ahead and mounted the ecu in place with the car off. I tried to start it once the ecu was mounted and nothing. Cranked but would'nt fire. Again no spark and I did'nt smell fuel. Since I had the other ecu handy, I unplugged the mounted one and plugged in the other ecu. It fired right up. Any insights?

Cris

[BMWCCA2]

Broken wire in the harness to the ECU?