1985 BMW 635CSI Starting Problems - No Spark


I just purchased Rob Siegel’s "Guide to European Automotive Electrical Systems, but have not had time to delve into it yet. I checked my fuses and relays, which all seem to be good, but I am not getting spark when I turn the engine over. Curious thing is that the battery is not slowly draining when sitting like it used to when it ran fine, so there must be a disconnect somewhere. The only thing that changed is that I washed down the engine, ran it for a minute and then it wouldn’t start the next time I tried it.
A little guidance would be appreciated.
Thank you! Brett


Interesting issue @brett1!

Not being a BMW expert like Rob, I would start with general ignition troubleshooting. Going straight to the coil and ensure it is still connected properly and getting power appropriately. Then I would move to the distributor cap and make sure no moisture got in and corroded the rotor or cap.

Keep us up to date on your findings, there might be someone else here with the same problem!


Sounds like you sprayed water where you shouldn’t have. Grab a can of WD40 and spray all of the electrical parts.


Does an '85 have a distributor? If so, be sure to check for water & condensation inside the cap.


Go to the BMW E24 bigcoupe.com website and do a search or join the forum. This problem has been addressed before IIRC. I believe it has to do with the main relay but not sure but the members of that forumwill almost certainly direct you in the right direct. BTW I also own a 1985 635CSi and just love the car. The 635CSi M30 engine does have a distributor but I don’t think it would cause the problem of no spark. What water would do would maybe cause a miss but not a total failure unless you really saturated things.


Thank you for the suggestions. No power at coil when cranking. Swapped main relay with new one, seems to be okay. I will update as I get further along.


So, after checking all my electrical connections, fuses and relays, it appears that a cat has been crawling into my engine compartment and knocked loose a connector from the OBC… She runs again! Thank you for all of the input, on to the maintenance and upgrades.