Replacing the fuel pump without the sender

[Riba]

I got the common problem with running out of gas on 1/4 tank, meaning the fuel is not getting transferred from the left side to the right. Already changed the fuel filter. Glad I did judging from the stuff that dripped out of it but it hasn't solved the problem. I can hear the pump faintly whining which is making me feel uneasy and as I am planning a longer trip I decided to do something about it. I know the perfect scenario is to get the new sender unit with the pump from the dealer, but as I am not planning to keep the car forever I would like to do it on a budget.
First of all, is there a particular reason not to replace just the fuel pump itself instead of the complete sender unit? If replacing the pump only, is there a particular one I should get (where?), or do I just get a generic cheap one from ebay and hope for the best? Hell, I can even keep the original one in the trunk if the cheapo one decides to give up the ghost, wouldn't mind changing it on the road.

Fire away!

[cn90]

Common issues in E39 forum (1997-2003 5 series).

- "Siphon Pump" failure causes fuel starvation when gas tank <1/4. When dealing with this issue, there are 2 options:
a. Replace the Siphon Pump
b. Learn a new habit of always keep gas above 1/4.

- Now that the fuel pump has been run dry a few times, there may be some very minor damage to the fuel pump (remember fuel pump needs to fuel to cool off). Whenever the fuel pump fails is anyone's guess. So, my advice for you on long trip is:
a. Keep a spare fuel pump in the trunk for long trips.
b. Print out procedure on DIY and keep it in the trunk, along with basic tools needed for the job. The key thing on long trip is: keep fuel between 1/4 and 3/4.
Above 1/4: to avoid siphon pump issue.
Below 3/4: in case you need to replace the fuel pump, you don't have to deal with full gas tank and its risks.

This way you are ready for this job, should you have to do it.

On the issue of brand name:

a. Do not buy the Chinese-made fuel pumps!

b. BMW OEM PN 16116755043 ---> $250.

c. Since the fuel pump is made by Pierburg, you can buy only the insert (fuel pump only) for about >$180:
New BMW E53 Fuel Pump No Send Unit x5 2000 2006 Pierburg 16116755043 | eBay

[Riba]

From the information I gathered it is very unlikely it is the siphon pump, as it is just a number of passive pipes. What is more likely is that the fuel pump is not generating enough volume of fuel to come back through the return line which in turn makes the siphon pump move the fuel from the left side using venturi effect. This can be caused also by the clogged fuel filter of course. Even if the pump is ok, I would rather replace it since the car has around 120k miles and I am not familiar with the maintenance history.

I completely agree with the rest of the info.

[cn90]

Not really.

When the siphon pump fails (search bimmerfest E39 forum), it fails. A new siphon pump will solve the problem of "stalling when gas tank below 1/4".

In your particular case, keep fuel above 1/4 for now.

For long trips, carry a spare Pierburg fuel pump and you are all set.

[Riba]

Thanks. I guess I will open up the tank one of these days and take a peek what is actually happening in there.