Fuel tank pump issue, level sender issue

[Collie]

2006 4.8is 2/1006 build date..

I figured I would ask before I spent more money. Vehicle started one morning ran for a second and quit. Crank, no start. Okay. Needs, spark, fuel, air. Fuel gauge reads 1/4 tank, but I don't hear fuel pump. Spray starting fluid in intake it starts. Got to be fuel pump issue. Pull rear seat, pull connector and test for voltage, no voltage to pump. All pump related fuses good. Switch horn relay with pump relay, same part, still nothing. Put voltage to pump and still no pump. All these test done alone, I really could have used a second set of hands. Figured I would just pull the pump out anyways. Put voltage directly to the pump out of car, no pumping. Figured previous test due to me being alone and not getting good connection and pump was bad. Ordered new electric pump and replaced it. Was going to put it back in and realized their was only a little fuel in the sump of tank.. I thought back since I had just parked it when the problem arose and think I had put fuel in it soon before this happened. So I thought maybe bad fuel level sender. Plugged assembly back up out of tank and manually moved float from full to empty position, never registered empty. Thought, okay, bad sending unit. Then I looked on real OEM to see the entire in tank assembly. It appears to show a line connecting to the right side assembly around the fuel level sensor, mine doesn't do that nor have somewhere to attach..? Searching online in a few places it appears there is also a level sensor on the left side..?

So, after this novel I just wrote explaining where I am. My questions are. Is there a sending unit on the left that works in conjunction with the one on the right for fuel level? But also, and more confusing. How is the fuel transferred across the fuel tank hump to the from the left to right side where the pump sump area is? The real OEM diagram makes it more confusing showing the line from the left side of tank to the right side connection to the fuel pump assembly which mine does not nor have a location to hook up..?

[Collie]

I just pulled unit out of left side of fuel tank.. There is fuel as well as another fuel level sender.. The unit only has two small two small wires and they go two the sending unit. There is no pump and as stated the hoses from left side of tank to the right so not connect to the only electric fuel pump in the tank. How is the fuel transferred and what is causing it not to transfer from left side to right?

[andrewwynn]

Find my detailed master thread on the fuel supply for the e53. Search for my username as started by. awr-fix should also be in the title. There is literally no more detailed description on the internet. Not even from BMW. They copied boilerplate from 5 series that doesn't apply to X5.

Some of the top points:

1) the electric pump is on the right side
2) the pump pushes fuel at roughly 65 psi to the fuel pressure regulator and filter
3) the FPR sends 50 psi to the fuel rail
4) the excess fuel pressure is used to send fuel at ≈ 18 psi back to the left side of the tank
5) the flow back to the left side goes though two venturi valves to suck fuel from the front and back to the pump well on the right side
6) there is a design defect that will eventually cause that Siphon jet to fail. Usually by 15-17 years or 130,000 miles. That can be fixed for a couple $ vs. replace the whole pump
7) when that fails you will fuel starve the engine when about 1/4-3/8 tank
8) once you are lower than about 28L of gas the car only "sees" about 5.0L of fuel, about 3.6 of that is not registered on the gauges.
9) the fuel filter is for all practical purposes lifetime, it can easily last 400,000 miles. However the FPR has an o-ring that will fail causing low and unstable pressure. They are usually sold as a unit.

[getty150]

Originally Posted by andrewwynn

Some of the top points
6) there is a design defect that will eventually cause that Siphon jet to fail. Usually by 15-17 years or 130,000 miles. That can be fixed for a couple $ vs. replace the whole pump
7) when that fails you will fuel starve the engine when about 1/4-3/8 tank
8) once you are lower than about 28L of gas the car only "sees" about 5.0L of fuel, about 3.6 of that is not registered on the gauges.

Tell me more about this please.
Fixing this for less monies.
I'm experiencing the 1/4 tank situation...I just changed out the fuel pump. But I don't want to experience this in the future...she has the e83 x3.

[Lucas.ua]

Simply said. It draws it from one side and returns it to the other. Right side has the pump which has 2 suction lines connected to it. The return is on top of the pump and the feed is on the opposite side.
2 level sender units. Check my post to see the replacement parts you’ll need. You don’t need the whole assembly!

Any more questions just fire away I’ve got mine out right now!

[getty150]

Question 1 what part is essential to replace?

[Lucas.ua]

It’s these that simply wear out over time

[getty150]

Yhis is extremely helpful...
Are they sold...?
I take it the sender arms swivel/slide here?
What are they called ?

[andrewwynn]

The resistance board for the level aren't a part I'm aware of sold. They can be cleaned and the wiper can be bent to increase pressure to get those working.

When that fails the symptom will be the fuel gauge will not go to full. The runs out of gas at 1/4 tank is a very different problem. That happens when the o-ring seal on the "sending unit" fails.

[getty150]

Originally Posted by andrewwynn

o-ring seal on the "sending unit" fails.

I like to see the location on the sending unit ....
Would I find this in the tank with the pump? Just trying to understand at rudimentary level.
Thanks

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