Date: Sat, 10 Apr 1999 20:12:09 -0400
From: "Nick G." <nikog_at_gate.net>
Subject: [E36M3] E36 fuel gauge explanation
There have been many reports of the fuel gauge in E36 cars not showing the
proper amount after refueling. My '95 M3 often has the same problem. I have
spoken with a mechanic at the local dealership about this, and he described
a few things to me.
On my car, if I let the fuel level get to 1/4 or below, and then refill the
tank *to the max*, the fuel gauge would read EMPTY, or stay at the 1/4 mark.
This would happen whether or not I had the key in the ignition.
The problem doesn't stem from the ignition key, but a bad fuel sending unit.
The E36 has 2 sending units, one to measure the 0 to 1/2 fuel level, and
another to measure the 1/2 to FULL fuel level. What usually happens (at
least in mine) is that the second sending unit (used to measure 1/2 to FULL)
has a bad contact point in its resistor winding, most likely at the FULL
position. When the gas tank is filled up, the second sending unit is
positioned on this faulty contact point, causing a break in the signal and
the incorrect fuel level reading. After driving a few miles, the fuel level
changes and positions the sending unit on a good part of the windings. Then
the fuel level reading is correct.
The fix is to replace the faulty sending unit. Filling up the tank with or
without the key in the ignition makes no difference, just coincidence.
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