From digest.v6.n224 Sat Feb 15 16:17:51 1997
From: "Brett Anderson" <bretta_at_webspan.net>
Date: Sat, 15 Feb 1997 11:41:57 -0500
Subject: <E36> Fuel sender description
> From: RL <r2l4_at_vitinc.com>
> Date: Fri, 14 Feb 1997 23:35:45 -0500
> Subject: E36 fuel guage reset , why?
> I have a 95 E36 M3 and have read many posts
> about the fuel guage causing problems like
> not going back to the full or remaining near
> empty upon fill-up. My car just did this
> today for the first time in 20,000 miles. The
> car was at 1/4 tank and at fill-up it went
> up a small amount and stayed there until I
> disconnected and reconnected the battery. Why
> does this happen and is it a repairable
> problem? Also, after reading through the wiring
> manual I noticed this car has two tank
> sending units why is this?
> Thanks in advance.
All problems are repairable, if the car is out of warranty, the only
problem is if you are willing to invest in diagnostic time.
There have been a lot of problems with the fuel senders burning their
tracks, although your problem sounds more like a cluster problem.
As for why there are 2 senders. The fuel tank is made up of 2 seperate
cells, one on each side of the car. The old E30's used a similar design but
had a transfer pipe joining the bottom of the 2 cells, in the E36 they
opted to do without the transfer pipe and use 2 senders instead.
A ground signal is sent from the cluster to the left sender, through it to
the right sender, which also has the pump, and back the the cluster. the
final signal is the sum of the 2 senders resistance, the more resistance,
the fuller the tank.
When you fill the tank, both sides fill as the tank is one at the top, the
fuel pump then sucks from the right side of the tank, the return line from
the engine bay empties into the left side of the tank. At the base of the
fuel pump is a shroud that ensures the pump does not loose prime with a
hard corner and a low tank. Inside this shroud is the end of a hose which
goes across the top of the tank to the left side, the suction action of the
pump creates a siphon with this hose, transferring fuel back to the right
side from the left.
When the car has a half tank of gas, the left side will be almost empty,
with about 10 Ohms of resistance in the sender unit, and the right side
will be full, will about 250 Ohms of resistance. The gauge reads 260 Ohms
out of a possible 500 ( or there abouts ) and says half.
Hope this helps those that are interested
From: Dale Beuning
Subject: <E36> Fuel guage reset
Saturday I was near empty on the tank, so I stopped to fill it.
I did something I've never done before when filling the tank,
I left the key in the ign, in the accessory position.
After filling and driving away, I noticed my guage didn't show
full, it was still down on E. The range also still said 30 miles
on the OBC.
Today it still didn't work, so I brought it to Camelback BMW.
They pulled out fuse #21 for 10seconds, then reinstalled it.
Presto, the fuel guage now works!
Moral of the story, key belongs in your pocket when fueling the car.
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