[TR] gas gage

[Ann and Tim Buja]

oliver wrote:
<snip>
> the gas gage goes left when i turn the car off, and then goes to
> 1/4 when i turn the car on.  period.  irrespective of how much
> gas is in the tank.  just all of a sudden as far as i can tell.
>
> what do i look for?  where do i start trouble shooting?

As already mentioned, I'd look first at the temperature gauge to see if it
is also reading consistently high or consistently low. If so, then replace
the voltage stabilizer on the back of the speedometer.  You should see
battery voltage pulses at the light green wire if you have an OE unit, or a
steady state 10V if you have a new voltage regulator style.  You should not
see a steady state battery voltage reading or pulses of less than battery
voltage on the LG wire.

If the temp gauge is normal, look at the fuel tank sending unit.  It will
typically have a resistance of 30 ohms at full, and 330 ohms at empty. You
should be able to measure this at the sending unit where the green-black
wire is connected, or at the connector next to the hood release cable at the
top of the driver's side A-post, or at the gauge itself.

You may have a float that has filled with fuel and is now a sinker.  To fix
this, you'll have to remove the sending unit and replace the float.  The
British Motoring Club of New Orleans had this on their Tech Tips page at:
http://www.bmcno.org/tech%20tips/techtip.htm

  FUEL GAUGE SENDING UNIT- If your fuel gauge never reads above empty,
  the most common cause is that the sending unit plastic float has
  cracked and filled with fuel. Instead of spending $50 for a replacement
  of the entire unit, you can get a brass float of the same dimensions
  from your local Ford dealer for about $10. The part number is COAZ-9202-B.

When you have the sending unit out of the tank, measure the resistance on
the terminal to "ground".  An analog meter with a needle is the best way to
observe this.  If you don't have one, connect the sending unit to the wiring
in your TR6, turn the ignition on and watch the fuel gauge. Move the arm and
watch the ohmmeter (or the fuel gauge).  You should see a smooth resistance
change from approximately 30 ohms full to 330 ohms empty as you move the arm
from one extreme to the other.  There should be no shorts or opens in the
sending unit - if so, you'll need to replace the sending unit.

Let us know what you find.

Tim Buja - Rockford, IL - 80 TR8, 73 Stag, 72 TR6