AWR-fix: e53 Fuel pump / siphon pump details

[andrewwynn]

Originally Posted by cn90

Mechanic checked: fuel pressure low, opened the tank, there was only 1 gallon in the fuel pump well!

There is always only one gallon on the right side once the total fuel quantity is about 1/3 of a tank.

If the fuel pump was submerged in gas the fuel pump itself is the likely fault.

The NORMAL reason for gas starvation when the gauge reads 1/4 for example is that the siphon jet connection is leaking at the o-ring. The left tank usually will have 15-20L of gas and the right side will mere ounces of fuel.

I would love to know what the follow up early with that car because what you are reporting doesn't logically make sense.

I have personally had the right side sensor hang up and that will give you a few liters of error. I hadn't seen a case of the left sensor hanging up but like I said if there's "a gallon of gas" on the pump side that's enough to drive 20 miles you won't stall unless the pump is worn out and can't provide 50psi.

[cn90]

The factory design is fine AS LONG AS the siphon pump works.
The BMW engineers did not anticipate siphon pump failure somewhere down the road!

What I meant is: build a tiny recess on the L side and put the pump down there. This way when the siphon pump fails, you can still drive until 1-2 gallons remaining.

Again, they did not predict siphon pump issue.

It is all because of the driveshaft tunnel issue...

[bcredliner]

Since new I have always run the fuel level down until readout is between 10-15 miles of fuel remaining. Still have original fuel delivery components with exception of fuel filter. Current mileage about 121,000.

[andrewwynn]

Confirm how much fuel fits when you say it is empty and reads 1/3.

A design flaw in the siphon jet that will give you an out of gas situation at between 1/4 and 1/3 of a tank of gas.

2/3 of a tank is 64 liters. If you can only add 17 gal then the gauge is correct and almost certainly your siphon jet is leaking.

100% of the BMWs that I've serviced the fuel supply have has the leaking o-ring problem. I will do preemptive maintenance on any BMW I maintain at about 120,000 miles or less because they have a design flaw that lets the o-ring come out of the groove and will not be able to pump the last 1/4 of a tank of gas.

You should be able to get 23-24 gallons of gas into the car when the low fuel light comes on. If your needle doesn't get below 1/3 and you can get a full fill then it's quite likely that one of the fuel level floats is getting caught up on the tank and reporting the wrong level.

[andrewwynn]

The o-ring will pop out of the groove because the fault in the design. It's a standard size o-ring but it's not a BMW part they only sell the entire unit.

I may have measured the o-ring look on the siphon jet repair thread. I've always had an o-ring on hand the correct size so I didn't need to buy one.

There also is a joint that has no seal but should have one and needs some Teflon tape to fix that also


Sent from my iPhone using Tapatalk Pro

[andrewwynn]

If your o-ring didn't dislodge yet, you just need to add a screw or a zip tie in the right place to prevent the failure in the first place


Sent from my iPhone using Tapatalk Pro

[80stech]

The o-ring only gets deformed from fuel pressure pushing on it when the plastic tubes get deformed/shrink/tilt and provides excess clearance. I took mine apart to check and everything looks like new. Not sure if in some cases like Andrewwynn's if it's poor quality plastic or ethanol in the fuel that causes the deformation/discoloring of the plastic or maybe a combination. Also I wonder if the problem wasn't corrected in later production and with a replacement assembly.

[andrewwynn]

It's the tilting. The assembly is only held together on one side opposite of where the forces are applied. I have not seen a change in the design to avoid the problem I think it takes about 4000-5000 hours to fail so multiply that by your average mph to determine when it might fail.
If there isn't and improvement in the design it will fail given enough time.


Sent from my iPhone using Tapatalk Pro

[andrewwynn]

Siphon pump DIY repair
https://r.tapatalk.com/shareLink?sha...8&share_type=t

That's the direct link to the siphon jet repair thread


Sent from my iPhone using Tapatalk Pro

[andrewwynn]

It's on purpose and makes more sense this way. They want the pump to be submerged in gas even when the car is at a sharp angle up or down.

By putting the pump in a 5L "dent" on the right side the pump is submerged when the tank has 0.0L on the gauge.

If the pump was in the bigger side it would take about 20L of gas to submerge the pump but more importantly when you are pointing down or up the pump would be dry.


Sent from my iPhone using Tapatalk Pro