At 12:26 PM 6/16/98 -0500, Dan Pockrus wrote:
> Like many other B owners, my fuel gauge doesn't work. I tried
>the Moss method of checking it, but it's been so long since I've used my
>test light that it may be busted as well. Suppose I whip out my trusty
>VOM? Should I be seeing voltage on the sender wire when the key is on?
>Has anyone tried this approach?
Dan and others, a quick test to determine if your sending unit, gauge,
wiring, or combination is at fault:
turn on the ignition and unplug your wire (not the ground wire) that
connects to your sending unit.
ground this wire and check to make sure your gauge reads full.
When your gas tank is full and your sending unit works properly, you have a
good ground connection, the sending unit will fulling ground, showing zero
ohms resistance. This resistance corresponds to a full reading on your
gauge. As the tank empties, the resistance goes up and your gauge should,
of course, react to show less fuel.
If your gauge does not respond then you need to check the gauge out. I'm
guessing here, but I imagine that the gauge has power to it and it grounds
through the sending unit. Check for voltage at the gauge positive terminal.
Now, if your gauge did peg the full mark, then you know that your problem
is either in the sending unit, or the ground wire. check the resistance of
your ground wire that connects to your sending unit. It should read 0
ohms, or you have a bad ground. If this checks out, perform one more
simple test before extracting the sending unit. connect a wire to your
ground terminal on your sending unit, and ground this wire. Does your
gauge read any differently than before? If so, you have a bad ground wire.
If not, then your sending unit is bad.
If the sending unit is the culprit, then you need to drain your gas tank
and remove it. When taking the retaining ring from the gas tank, be sure
to use either a brass drift pin, or a piece of hardwood. No need to
generate any unnecessary sparks.
After removing the sending unit, connect your VOM to the terminals on the
sending unit (Note: I believe some MGBs have either a ground terminal, or
the body of the sending unit is the ground). Move the float up and down
and note a change in the resistance. If there is no change, or little
change, then your sending unit is shot. By little change, I'm talking
about less than 50 ohms. I believe a normal unit should show a change of
around 200-300 ohms between full and empty, but I could be totally off. If
your sending unit shows good resistance change, then you may very well have
a good unit, but that should not be the case, if you preformed the above
tests on the ground and gauge.
Jay
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