Fuel pump issue

[e30jr88]

Hey guys I have an inconsistent fuel pump issue with my 91' 318i(M42).
For some reason the fuel pump doesn't always get power(no priming), about a month ago I had an issue and after changing negative battery cable and cleaning the connection on the fuel pump I was able to make it work.

It ran fine for about 3 weeks, about 3-4 days ago it did not want to start(since fuel pump not getting any power, couldn't hear it prime when in ON position). I changed the Relay for the pump and still didn't want to start. This morning I was going to start to figure out what was wrong, before I popped the hood I decided to give it a try to see if it would turn on. To my surprise, the pump primed in the ACC position and the car actually started!

My question is what could be causing this inconsistent power issue to the pump?
Since it works for a couple days and then decides not work after sometime. (pump doesn’t prime)
- I have replaced the Relay
- Cleaned connections at the pump

[jlevie]

A 91 318is could be different, but no other E30 that I've ever seen primes the pump. The DME only engages the fuel pump relay when it sees timing data from a rotating engine. Does the pump run when cranking? And if so what is the fuel rail pressure?

[vpilarrt]

The 318is is the same as the other E30s as far as fuel pump operation goes.

[e30jr88]

I don't think it's a pressure issue but more of a electrical issue, since the car is actually turning on and driving today. The pump does make a small noise when its working properly and the relay makes a clicking noise too.
The thing is sometimes it randomly doesn't want to turn on and I dont hear either the clicking or the pump making noise.

Since the car is driving right now, that means there is pressure and the pump is priming, I have no idea what was wrong and how it "fixed" itself.

So I'm thinking maybe there is a failing sensor somewhere or a bad connection but I don't know where to begin searching. Specially since the car actually drives right now.

[vpilarrt]

Could be that the pump is going bad. Have you noticed that its been getting louder recently?

[603Racing]

If you don't hear the clicking (relay) then you may have a relay going bad. Or there is a wiring problem. Not much involved with getting the relay to "click". Power and ground, ciruit activated by the ignition switch being on the ON position.