<all> Check your Fuel Transfer Pumps!

["Aaron Bohnen" <bohnen@xxxxxxxxxxxxxxxx>]

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
___________________________________________________________
Aaron Bohnen                     email: bohnen@domain.elided
- -Ph.D. Student, Civil Engineering Department, U.B.C.
- -Technicraft Engineering Services

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