2004 330ci ZHP no volts at fuel pump.
Couple days ago it started missfiring/loosing power accelerating onto onramp. Made it home (barely) sputtering whole way. Checked glovebox and ebox fuses under hood/good. There appears to be 5v. at one of the wires at fuel pump at all times, however with ign. in run position there is not 12v. at the pump. How do i get to the fuel pump relay behind the glove box?, i wanted to try swapping the relays to see if the pump would run. Could the MAF sensor have anything to do with the voltage missing because my code reader brought up the MAF once allong with four cylinder missfire codes as well as an intake air sensor code.........Thanks for any help, Robert.
Your car needs a fuel pump either way. Trust me.
The 5V at the pump is a supervisory Voltage the DME sends to the pump.
12 Volts or something close to 12 Volts is only supplied for the "Prime" cycle which is for only 2-3 seconds when the key is initially turned on. Many Voltmeters are not able to capture the prime cycle.
You may be able to capture 12 Volts while cranking, however, depending on how the circuit is wired the relay may not pull down without a load? I cannot recall the exact behavior of the circuit for sure.
This happens ALL the time, where there is too much focus on measuring 12 Volts at the pump and it cannot be reliably found!
If you want to swap the horn and fuel pump relay, they are behind the glove box, door and liner need to be removed, they are the darker green relays that are the same color. I think the far left and middle relays?
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