94 730i fuel pump fuse keeps blowing

[Nisaja]

Hey guys.

I recently bought a 1994 730i with a whining fuel pump. The indie BMW workshop I took the car to couldn't find an E38 pump, but found an E39 pump with the matching LPH (Liters per hour) rating. They installed the pump to the E38 pump assembly and installed it. The car ran fine for a few days. Then the fuse blew. Replaced the fuse and the car ran for 2 weeks. Again, blown fuse. I'm wondering what this could be? Could it be the pump itself or some other electrical issue in the car?

Thanks a lot!

[Timm]

The E39 pump takes the same current so should be OK - my guess is the insulation on the in-tank wiring to the pump has fallen apart as they often do.

[Nisaja]

The E39 pump takes the same current so should be OK - my guess is the insulation on the in-tank wiring to the pump has fallen apart as they often do.

Thanks for the reply. How sure are you that they all take the same current? Mine is a 730i, so a 3 liter V8. Not sure if you guys that that model.

Isn't the in-tank wiring inside the fuel tank? Isn't that a potential fire hazard?

[CD05001CIA]

Thanks for the reply. How sure are you that they all take the same current? Mine is a 730i, so a 3 liter V8. Not sure if you guys that that model.

Isn't the in-tank wiring inside the fuel tank? Isn't that a potential fire hazard?

That's why it is fused AND why you should fix it. (rolls eyes)

[Nisaja]

Hey guys. Sorry for the delay.

The cover for the earth wire was damaged at one spot. We welded that up. Sadly the same thing happened again after a few days. Car didn't start back up after stopping. Removing the fuse and plugging it back in fixed it!

Took it back to the workshop and checked the current draw for the pump. It was 6.5 amps. Really stumped.

The cover for the ribbon behind the instrument cluster is damaged, causing all the wires to short. My temp gauge read above the middle and sometimes all the lights on the cluster would light up.

Could that have something to do with this? We fixed that by separating the wires.

Didn't drive the car much after that. The fuel tank started leaking. Fuel was spraying underneath the car. Checked the fault codes and found a few about the fuel tank ventilator lines being clogged. Seems like the tank is pressurized. I read a couple of posts about fuel tank implosion. Guess that's what's happening to me.

[Nisaja]

Update.

So the fuel tank imploded. Started leaking from the middle. Checked the codes and got a few for the ventilator lines. I'm assuming they're blocked. Should've seen it coming. The gas cap always made a pshh noise when opening. Read here that a cheap fix is to drill a small hole in the gas cap. Did that and fixed the leak.

Now, before this, the fuel pump would make a faint whine after about an hour of driving. Not loud enough to notice, but if you bring your head close to the rear tire, you hear it. After drilling the hole, I'm not hearing anything at all. So I'm guessing the pump was working harder before, because the tank was pressurized.

Could this be the reason for the blown fuel pump fuse? The pump worked harder and harder as the tank got pressurized, drawing more and more current, until the fuse blew?

[CD05001CIA]

Update.


Could this be the reason for the blown fuel pump fuse? The pump worked harder and harder as the tank got pressurized, drawing more and more current, until the fuse blew?

No. fuse blowing much more likely, -> damaged wiring <- faint fuel pump whine-ing normal because fuel travels in a loop to a fuel scavenger that moves fuel from far side to pump side.

[Nisaja]

No. fuse blowing much more likely, -> damaged wiring <- faint fuel pump whine-ing normal because fuel travels in a loop to a fuel scavenger that moves fuel from far side to pump side.

I checked out the wiring. Couldn't find anything wrong. I've read here that the fuel pump fuse blows when the fuel filter is clogged up. It stresses the pump more so it pulls more current to keep working, and then Ultimately the fuse blows. Isn't it the same story here? Tank under pressure and pump trying hard to suck the fuel out of it?

[Nisaja]

Well guys, it seems like drilling a hole in the gas cap fixed everything. Fuel pump doesn't blow the fuse. No whining sound from the pump. No leaks from the tank and no implosions.

I guess it was all because the tank was pressurized and the pump was working harder to get the fuel out of the tank, and that causes the fuse to blow.