The missus has a BMW325 diesel c@r. It has for a few months now has random starting (and random stopping!)trouble. it always seems like a fuel blockage or air in the fuel. But each time I get to looka at the car after a brakedown there is nothing wrong with it.
I finally discovered the problem.
it has a sadle shaped fuel tank. When you fill up the fuel only goes in the right side of the tank unless you fil right up and then the fuel goes over the hump and into the left side. The engine takes fuel from the left side. both sides have a fuel level sender. when the fuel in the left gets lower than the fuel in the right a transfer pump (is suposed!) kicks in and top up the left side.
There is some trouble with the electrics which I have narrowed down to the wiring between the left side or the control unit that switches the pump on.
Both senders work. The resistance scale in both senders is 10ohms empty 130ohms full. Can you rig a ciruit that will work on the logic of.
when left has lower resistance than right switch the pump on till right is =to or les than left?
If it was me Id just have a switch for the pump and live with it but she cant be doing with braking down when you forget to pump fuel over which I can understand.