For about $200 you can solve any fuel problems for years to come. Replace the fuel pump, fuel filter, fuel pump relay. It's 99% the fuel pump. Just hope you don't have the SULEV M56 engine.

 

See 2nd link below in my signature.

The fuel pump will likely always have a very low Voltage present until Prime or Cranking.

Worry less about the Voltage and realize you likely need to replace your fuel pump if it is not working. You can swap the horn relay and fuel pump relay for a test, but likely not worth the effort, the pump is easier to change then getting at the relay in my opinion!

 

I have the M54 engine, thank god. The bad fuel pump could still explain the low voltage? I already have one ordered anyway and I think it was one of your posts from a while ago that suggested I replace everything. The low voltage is the part that's confusing me.

 

5v is normal at the pump when it's not running. Google "fuel pump voltage site:e46fanatics.com". I suspect it sends 12v to the pump only when it's running but it becomes difficult to test that because the harness is connected to the pump.

Your symptoms do point to the fuel pump itself. Mine failed at 89k miles.

 

Yeah i don't get the low voltage either. maybe the car switches voltage once fired up?? maybe someone else here can test theirs. Teddy? your car is gutted out so you should have quick access with a multimeter

 

Maybe the DME needs the signal from the crank sensor to apply full voltage.

 

good. we don't need teddy afterall. teddy you can take your drift shoes back off and hang them up. go back to bed

 

Well, it seems its always something with my car lately.

I'm in the same club as well. Good luck OP

 

Thanks for all the help and verification guys. Hopefully I may be able to get that fuel pump in today and all goes well.

 

Report back when you do, good for the archives.

 

The DME sends a supervisory low Voltage to most circuit when not energized. Usually this is 5 Volts, sometimes it can read higher when the load on the circuit is not present.

12 Volts, or usually 11 and change, is send to run the pump during prime, a very short period of time, maybe 1-2 seconds, then while cranking. The reason the fuel pump does not always have 12 Volts present is for safety reasons. The DME has to see a crank signal and/or oil pressure before the fuel pump relay is energized. This is in case the engine stalls or the car is wrecked that the fuel pump does not continue to run and when you sit in your car with the key in position 2 the pump will not run until the DME pick up crank signal and/or oil pressure.

I cannot recall 100% if BMW follows oil pressure, but it is usually a wise idea to shut the fuel off when there is a loss of oil pressure. It likely will save the engine and get the drivers attention, however, this also leads to the likelyhood the engine can cut off in traffic so it is a double edged sword. Protect the engine, or protect the occupant??

I think at the end the day the lawyers decide what happens anyway!!

 

Well, I got the new pump and plugged it in and turned the key on and it did kick on so the pump was definitely the issue. However I'm having some trouble getting the old pump out. The black hose on top of the pump is being a real pain to get off. Also the metal ring that screws down around the pump isn't budging. I'm think I'll spray some WD-40 or something under it to help break it loose. Any tips to get that black hose off? There's not a whole lot of room to pull on it. Thanks in advance.

 

UPDATE: I got the new pump in and everything is running smoothly. I did have to put a new hose clamp on the line. Thanks again for all the advice!