91 525i Won't start

[ctroxtell]

I hope someone can help me, my 525i just stopped running. It was at least starting and then cutting right back off but now it won't even start. Car turns over but won't start up. Fuse 23 is good, I pulled the main relay and tested the voltage...its jumping from OL up to 16v consistently, the fuel pump voltage signal is getting this same voltage. What would cause the voltage to jump around like this?

[BMW IDFR]

This is a textbook case of the Crank position sensor.

When they are failing, they fail to send the "engine started" signal to the DME, and cut out after start.
Eventually it will stop starting.

Your car is similar to mine and I went trough this too.

*Assuming the fuel pump is doing it's job*

[cochise325]

Definitely check the fuel pump.

[FernandoBunster]

The first thing I would do is check to see if you have gas in the tank. This happed to me a few weeks ago with my '95 Touring and it turned out to be an ambitiously reading fuel gauge. Added some gasoline and it started right up.

[ctroxtell]

Just wanted to post what I had determined. First off if your going to take readings with a multimeter, make sure you know how to use it and have it in the correct range, I grabbed my newest meter and had it in AC mode. My fuel pump was what had died on me, luckily I had a great help, another local BMW fanatic let me have a spare pump he had and I was back up and running in no time. Found a large O-ring in the gas tank also...not sure where it came from.

[mdimillo]

I had the same symptoms, changed the fuel pump and wasted $200 (aftermarket Aeromotive). It ended up being the crank position sensor. Either unplug the connector and test it, or unplug the ECU and test the proper pins. You can find the pin #'s if you can get your hands on an electrical troubleshooting manual for the E34 (common PDF). If you want to rule out the fuel pump, jump the relay terminals.