Re: Help...92 535i

["Michel Drainville" <MDrainville@xxxxxxxxxxx>]

Dennis,
I troubleshooted a similar problem on my wife's ex VW Cabriolet.

Start by checking if 12v is at the pump connector when you start. Don't use
the body as a ground, but use the two wires of the pump connector. You may
have 12v referenced to ground(the body) but, the negative wire of the pump
may be broken. If 12v is present at the pump, the pump is defective. If no
power, check if the ECU is outputing 12v on the output pin to activate the
fuel pump relay. If yes, check if the relay really engage (mechanically).
If it does, check if the relay is receiving 12v from the battery. If OK,
check the output of the relay if you have 12v. The contact of the relay may
be burnt or having a high resistance, which will give you 12v without load,
but when the pump is connected, you may have only 8V (V=RI).

If the pump is working when starting, but stops as soon the engine is
started, it may be related to the AFM circuit. When starting, the ECU gives
power to the pump, but when the ECU sense RPM on the engine, it checks if
the engine is still running using a switch in the AFM box (I'm not sure if
BMWs use this method but Toyota does). If no air flows into the AFM, it
means the engine is stalled, and the ECU stops the fuel pump.

I hope these tips will help you solve your problem.

BRs
Michel Drainville
91 318ic