Date: Wed, 9 Sep 1998 00:02:00 +0000
From: "Aaron Bohnen" <bohnen at pop.unixg.ubc.ca>
Subject: <all> Check your Fuel Transfer Pumps!

Hi everyone,

I have come to a scary conclusion. More than half of the not-brand-new BMW's I've inspected during the last week or so, both at wreckers and driving around, have inoperative fuel transfer pumps. This is bad!

This condition puts added strain on the main fuel pump, eventually leading to the demise of the main pump. It also has a bad effect on driveability, effectively reducing the fuel flow rate and pressure - causing the car to run lean.

Although the transfer fuel pump is quite an expensive part and generally sold as a complete unit which includes the fuel pickup/strainer assembly there is another way around the expense. If you do not need to replace the strainer/pickup assembly you can replace only the transfer pump itself.

This must be done with aftermarket parts - BWD and Niehoff both make suitable transfer pumps that cost approximately a third to a sixth of the complete pickup assembly. The classic kludge is to the order the transfer pump from a '73 Vega which is said to work. I would be very careful about that - take your pickup assembly with you to your parts supplier and be very sure that the strainer assembly will fit onto the bottom of the new transfer pump.

If you do this kludge fix you will also have to do some soldering. I suggest out and out replacement of the power wire leading from the cap to the transfer pump. Most of the older cars' pumps used wire whose jackets were not entirely impervious to gasoline. I suggest complete replacement of this wire with a silver-plated copper, teflon-insulated piece, with carefully soldered end-connections and a good dose of high-grade shrinkwrap for the ends.

You will also have to fabricate a bracketing scheme for the pump into the pickup assembly. Some high-grade tubing and Zip-Ties make a very secure mounting scheme. Do not increase the diameter of the package much at all since it won't fit down the hole in the top of your tank if you do.

Result: much better driveability (less of flatspot mid-band and also more oomph from a standstill - feels to my butt-dyno like at least 10 to 15 more horsepower. Honest!)

Cost: much less $$$ than a BMW pickup assembly.

Verdict: check it. Replace/Repair/Kludge as necessary.

best regards to all,

Aaron

• -Ph.D. Student, Civil Engineering Department, U.B.C.
• -Technicraft Engineering Services