Might be EZ fix. Check 635csi part # before swap. (archive)

Your problem sounds like a bad solder joint within the computer. There is a large transistor in there that is used for ignition timing control. The solder joints between that transistor and the circuit board can fail. If you're handy with a soldering iron you can fix it yourself. If you look through the archives you should be able to find instructions on how to do this.

You could try simply reseating the connector on the computer. You have to push a spring loaded clip at the back of the connector, then pivot it out toward you. It's tough, but it'll come. You won't be able to actually remove the connector, but you don't need to. Just reseat it and try starting your car again.

I wouldn't swap with your 635csi. The '86 535i uses Motronic part # 0-261-200-059, and the '89 635csi uses part # 0-261-200-179. I don't think they even use the same connector. If your 635csi was an '86 as well, then it'd word. Sorry.

86 535i has no spark. Checked everything out and I am down to computer or wiring harness to computer. Key symptom is if I pull down on compter in glove compartment the car starts but will not keep running when I let go. I need help for info on some one to diagnosis computer so I can isolate my problem. Has anyone had a electrical problem isolated to the computer wiring harnes. I also own a 89 635CSI, can I use that computer to isolate my problem?

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