Fuel pump sender accuracy with BW e36 dual fuel pumps

[retrogrouch]

Has anyone had success in getting their fuel gauge to read accurately after installation of BW dual fuel pumps? I recall the passenger tank gets fed from the driver's side. Maybe that's the issue because my gauge typically won't fall below 1/2 tank reading even if the fuel volume is fairly low.

Even the super gurus have been stumped by this. I suppose that accurate assessment of fuel tank volume is impossible given the inherent design of the stock senders and the fuel starvation fix.

Thanks for ideas.

[m3bs]

Each pump has a level sensor, and the two air wired in series. One sensor is probably stuck, or shorted since you don't ever see below 1/2. Per the Bentley manual the individual sensor resistance should be about 10 ohms empty, 250 ohms full. Disconnect the white connector and see what kind of resistance you have at each sensor.

[jayjaya29]

When installing the driver's side pump you have to be very careful with its orientation so the float has full travel range.

[NeilM]

When installing the driver's side pump you have to be very careful with its orientation so the float has full travel range.

Exactly.

Following are my installation notes from 2003 which I sent to Bimmerworld. The dual pump setup has worked perfectly since then, allowing me to run at least down to the reserve light under track conditions. Note that all these notes refer to the Bimmerworld kit as it was then. It may have been changed since.

This message is to report how the installation turned out for me, and to
offer some suggestions. In each case I verified the left and right side
sender readings individually using an ohmmeter on the external terminals.

(1) My first installation put the DS pump in the standard orientation.
(Looking toward the rear of the car, the electrical sockets on the pump are
at the 6 o'clock position, and the suction and discharge ports both point
away from the transmission tunnel.) This resulted in the DS float hanging up
internally and failing to read a correct full tank value.

(2) I reinstalled the pump with its body rotated about 90 degrees CCW. I now
got a correct full reading, but the float apparently hung up as fuel level
dropped. The gauge showed almost 3/4 tank when in fact there was less than
1/4 tank remaining. Not good!

(3) I now tried Andrew Kalman's modification to the float mechanism, see
<http://www.pumpkininc.com/content/doc/guide/ag-8.pdf>, which involves
changing the orientation of the pump's float arm pivot. You can see this in
pages 13-15 of his instructions. I then reinstalled the DS pump in its
normal orientation. The sender now gave a correct low fuel reading, and
after refilling the tank the car's gauge indicated full. Success!

A couple of notes about this. Rotating the sender float pivot makes it hard
to get the pump mechanism through the aperture into the tank. I had to
remove the rubber sealing ring for extra clearance, and then refit that
while holding the pump up a couple of inches. This was somewhat fiddly to
do.

Other aspects of Andrew's installation aren't the same as Bimmerworld's. He
brings both the suction and discharge lines from each side to T-connectors,
whereas BW uses the second pump solely to transfer from one tank half to the
other. I prefer the BW system because without non-return valves, Andrew's
might result in air being pumped into the fuel line if the DS tank half runs
dry. The BW plumbing layout is also a bit simpler, avoiding the need for
T-connectors.


Some additional notes about plumbing
====================================

With the DS pump now in standard orientation, both the inlet and discharge
ports point in the wrong direction. I found that the hoses tended to kink
when looped around to the ports. At the hardware store I bought ordinary
coil springs about 5" long of similar or slightly smaller ID to the hoses,
and inserted them into the pump end of each hose. This prevented them from
collapsing or kinking when bent in a tight radius.

The bulk of the BW adapters makes clean DS hose routing difficult, and
aggravates the kinking problem. I did two things to get around this.

First I substituted 5/16" (roughly 8 mm) ID hose for the external crossover,
and connected the adapter to a very short length of the larger 12 mm hose on
the passenger side. There's plenty of room for it over there, and the
adapter now installs in a straight line.

Then for the DS return line I dropped a length of the 12 mm diameter hose
down in front of the tank toward where the connection to the hard line is
made. I installed the BW hose adapter in this vertical run just above the
hard line connection, using a very short length of 5/16" hose below the
adapter. The larger hose still fits OK in the stock plastic retaining clip.

The end result is that both adapters are now removed from the DS pump area,
allowing for better hose routing.

If more hose becomes necessary, make sure ONLY to buy automotive fuel
injection hose. You can find this at any auto parts store, or at a BMW
dealer.

To that I'd add that the first "half" of the full tank lasts longer than the second one does, but it's close enough.

Neil
96 M3

[lightingflash]

Mine seems fairly accurate and I followed the instructions as above. I can not however run on the track down to the reserve light. I start getting starvation before that.

[E39SD]

Exactly.

Following are my installation notes from 2003 which I sent to Bimmerworld. The dual pump setup has worked perfectly since then, allowing me to run at least down to the reserve light under track conditions. Note that all these notes refer to the Bimmerworld kit as it was then. It may have been changed since.

Thanks - copied and will file in the box with my as yet uninstalled Bimmerworld kit.

[retrogrouch]

Great info and I'll re (re- re, etc) check this.

Mike

[retrogrouch]

BTW, this really did the trick. I've been too chicken to run the car below 1/4 tank, but I'll try it some time.

I followed the directions about rotating the float mount 90 deg, removed a lot of the white, plastic pump material with a dremel, and bent the float arm a slight amount. I made sure the float arm moved freely through its range.

Thanks for the info and the link!

M

[thedizzle]

Mine are pretty accurate but as soon as I get to the 1/4 I'm dangerously low and have the potential for starvation even with the dual pump kit.