BMW Repair: 1986 BMW 735i, inertia switch, crank pulley

Question
Hi,
I have a 1986 735i, it was running fine then one evening I went over a rough spot in the road and the engine died, I coasted to a stop and about 5 minutes later it started again, this happened two more time then it finially just will not start. I change the Dist. cap, rotor, wires, plugs and fuel pump (which was leaking)and it still will not start, it does crank. I checked the spark and "no spark". I cranked the engine when the dist. cap was off and the rotor is turning. I do know that when I went over the rough spot in was bumpy and thats when it died. Is there a reset somewhere or a relay that may need to be changed. My next step was to check if feul is being pumped up to the injectors... I was told if there is no spark and not pump action it may either be a fuse (which I checked them out) or a relay that controls both.
Is this info correct or am I barking up the wrong tree

Answer
hiya!

Mmmmmm, A couple of questions first.... do you perhaps have a huge bunch of keys on the ignition key? If so, you might have a weak ignition lock, it's been known to happen. Did you (before the incident) have to jiggle the ignition key in order to start the car?

If no to the above then we have to look elsewhere, like the Crank Position Sensor or perhaps a bad earth. Firstly check out the CPS positioned on the crank pulley. Check for resistance (1-15 Ohm). If that's ok start checking the earth connections are all clean and secure. It always pays to remove the battery negative cable while you set about cleaning all the contacts (including relays)with WD40 that you can get to including checking the ECU for any signs of damage (check that there was no water that could have got in while you were on the bumpy road).

I don't know if your car has an inertia switch, have a look in the handbook. But if it does check that out as well.

Also, do you have an aftermarket immobiliser fitted? If so check it for connections as well.

Generally speaking it sounds like an earthing/connection issue as the problem arising at the same time as hitting a bump seems too coincidental.  

Good luck and let me know if you have any luck!

Sorry if I can't be more precise but it really is going to be a process of elimination to get to the issue.

Regards

Rob