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Fuel Transfer Pump

How do you know the transfer pump is dead?

It is dead ..

Here's how I determined that ..

First .. main pump is making loud buzzing sound ..

Second .. Access the transfer pump, borrow stetoscope from Nurse Wife
          (Annie .. get your gun ;)

Third .. bypass fuel pump relay and listen to transfer pump ..

Now you WILL hear what sounds like the xfr pump working, but it is really just
a column of sound from the main pump, up an hose of incompressible fluid (gas)

So ..

Fourth .. Listen to the xfr pump area while disconnecting and reconnecting the
          xfr pump connector (smaller 2 pin job) .. hmm .. NO CHANGE in sound

Which means ..


   :) :) :) :)

Replacing the transfer pump.

Date: Sat, 23 Apr 1994 18:16:07 -700 (MDT)
Subject: Fuel Transfer Pump on 1987 325is
To: bmw 
Mime-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII

Well, bought the part earlier today at the dealer .. 101.00 v. 13x.nn list
(Noble wanted 99, so I wen't with my dealer!)

Simple job, 15 minutes max .. 

Thanks to all the tips ;)

BTW, I used a handivac to cleanup all the dust on the top of the tank,
before opening anything ..

Here's what I did .. (just for posterity and others who may have to do this)

1) Remove lower rear seat cushion, and remove access cover .. clean up dust!

2) Disconnect 2 sets of wires, 1 for sensor, 1 for pump

3) Remove 2 orig. clamps (with diag. cutters)

4) Remove 4 nuts and washers from sensor ..

5) Slowly remove sensor to avoid gas mess ..

6) Remove 2 hoses from xfr. pump and rotate and remove pump

   Note: once you have "unlocked" the pump, you'll have to turn it around
         a bit to remove the pump from the gas tank ..

7) Reassembly is the reverse, using 2 new hose clamps and 2 new o rings ..
   1 is included with the pump, and the second fits on the sensor and costs
   3.00 (big deal) .. don't forget to pry out the old sensor o-ring which
   fits into a recess under the sensor bolt flange, around the sensor body
    tube .. use a paper clip ..

I detailed this for 1 main reason, note that the best way to make sure that
nothing falls into the tank, is to make sure that nothing is NEAR the tank
opening that CAN fall in (like nuts, hose clamps .. etc ..) :)

OH, AND BTW .. a bad transfer pump DOES affect idle quality .. once I replaced
the pump .. I restarted to check for leaks .. it took about 15 sec. for the
buzzing to stop as the system assumed proper pressure ..

Then on the test drive, my idle now stays ROCK steady and smooth ..

Can't wait to do the valves and plugs tomorrow !

(94 325i / 87 325iS w/ new xfr pump ;)

Using a AC-Delco pump

On some models, the ones that use a metal housing-ed pump with detachable bracket, you can buy an identical pump from you local AC-Delco parts supplier. It's the same pump as used on some GM cars (the Vega was one, I believe). A lot cheaper than buying the whole pick-up assembly from BMW. Also, Volvos use the same transfer pump, so you can sometimes use the transfer pump off of an '84 or later Volvo. Volvo sells their pump seperately. However, some BMW's came with a plastic VDO transfer pump. This unit is not replaceable, you need to buy the whole pick-up unit. A metal pump can be retrofitted, but you need to find a bracket for it. (the plastic pump has a built in bracket) Still researching this one. Hope this helps, Ben

A real Kludge

From: (Sam Chien-shin Lin)
Subject: Transfer Pump & Strainer Kludging (long)
For the past year, I've been told by the local dealer and other BMW shops that I should ignore the incessant buzzing sound coming out of my '85 325e's fuel pump. With all the ongoing discussion of transfer pumps lately, I began to get suspicious that perhaps my transfer pump was to blame. So, I decided to investigate this past weekend...

Taking out the rear seat and jumping the fuel pump relay, I crossed my fingers and prayed that the transfer pump was running. Just as xxx XXX said, it's really hard to tell over the racket that the main fuel pump makes. Putting my ear up the the transfer pump and connecting/disconnecting it, I couldn't detect any change in sound. So I hooked up my ohmmeter across the transfer pump, and got an open circuit. Not good. Removing the pump and hooking it up directly to the battery, I came to the dreaded conclusion: it was dead. kaput.

ARGHH! Not another $100 again! After all the hundreds of $$$ I've poured into this car over the past 2 years, I wasn't about to be licked by this one! Ben Thongsai mentioned last week that AC-Delco transfer pumps from a Vega might retrofit nicely in cars that have metal transfer pumps. Lucky me...I had that plastic one instead, which has the bracket molded directly into it. With very little hope, I trucked out (in my 2002, the car that RUNS!!!) the the nearest Pep Boys, and asked for a Vega transfer pump. "What year?" the counterman asked. "I don't know...what years were Vegas made? I want to put it in a BMW." He shook his head in disgust, but then came back with a pump. Hmm...same diameter, but no bracket, and it was about 3/8" shorter. Amazingly, though, it had screw-on terminals w/ the same terminal orientation as my VDO unit, and the pickup screen even fit! I paid $29.48 for a BWD P1 pump and $1.99 for a pack of hose clamps and headed home.

BTW, the dealer doesn't sell the strainers separately - YOU HAVE TO BUY THE WHOLE PUMP!!! Pep Boys sells a BWD F4 strainer for $4.12 which fits nicely on the VDO and the BWD P1 pumps. It is a different design from the BMW part, but the fitting is the same, and it appears to have more surface area than the BMW part, so it should flow better. Anyway, it's 70 micron polyester mesh.

Ok, you purists...those who wince at the thought of parts lacking BMW logos in your precious Bimmer...avert your eyes, because what I'm about to describe will make your stomach churn...Yes, I did it...I INSTALLED A CHEVY VEGA TRANSFER PUMP - not even OEM AC-Delco, but an AFTERMARKET BWD unit! It comes with a lifetime warranty, BTW.

The hardest part of the kludge was popping the rivets that held the positive wire and the brass negative strap onto the old VDO pump. Looking carefully at the VDO unit, I noticed that the mounting bracket had an outline around it, which would leave just enough extra plastic to clamp on my hose clamps. I got out my hacksaw to cut along the outline and used two hose clamps to clamp the bracket onto the Vega pump. After some fiddling, I was able to adjust the positioning so that the wires would reach and the short rubber connecting hose would fit. Using the screws supplied w/ the pump, I connected up the terminals and Voila! Done! When I tried to install it, I ran across an unpleasant surprise...the hole in the fuel tank is such a tight fit that the hose clamp screws wouldn't clear; I couldn't get it into the tank no matter how I tried. Back to the drawing board...

I had to throw away the mount I cut out of the old pump, was too thick to fit into the fuel tank. Finally, I got a short length of fuel line hose and slipped it over the fuel return tube (for shock absorption and traction) - the fuel return tube is what the mount/negative terminal is welded to, and then secured the pump to the hose-covered return tube with two large nylon wire ties (the zip-on type). It might not sound secure, but I pulled on it hard, and it was firmly secured. This time, it fit into the tank w/ room to spare.

Not only is the buzzing gone, but the severe midrange RPM flat spot the car's had ever since I had it is gone! It definitely accelerates faster and smoother now. Hopefully, the main fuel pump isn't already roached from running it so long w/o the transfer pump.

Was the effort worth it? Maybe not in terms of money saved per hour, but it was worth it to keep the $120 out of the dealer's sticky fingers. The kludge took about 1 hour including the failure of the first mounting method.

BTW, the later models do away w/ the transfer/main pump setup, and have only one pump in the gas tank. Does anyone know if these can be retrofitted in the older models? If the main pump goes, I'd like to just bypass it and install in the newer in-tank pump if possible. -Sam