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MG MGB Technical - Incorrect fuel gauge reading

My Smiths fuel gauge reads 3/4 when the fuel tank is full on my MG B GT. I have changed the tank sender unit, the voltage stabilizer and now the fuel gauge but it still reads 3/4 when full. Any help appreciated.
B Powell

Ground the contact at the sender unit. With ign on the guage should read full. If it does then the wiring is OK.
I would check any grounds I could find. To me, it sounds like high resistance some where.
Other more knowlegable(and better spellers) should chime in soon.
Good Luck
Steve
Steve

Thanks Steve, will have a go on the weekend.
Brian
Brian

I had problems with my fuel gauge not reading correctly but sorted it by calibrating again.

First I made sure sender was in good order (fitted a new en) and fitted a voltage stabilizer.

then the fuel guage was removed but left wired in.

then jacked the car up (knowing not much petrol in it) so the sender unit could be removed without leaking fuel - again leave wired up (make up a temp earth lead).

turn ignition "on"

then move the sender float to where it would be if "full" and adjust the gauge to show full.

then move the sender float to where it would be if "empty" and adjust the gauge.

see link for calibration instructions...... http://www.mgb-stuff.org.uk/wn_fuelframe.htm
S Longstaff

In my experience with two cars this is normal when changing the sender from the original to current stock, you have to adjust the gauge to compensate, as the real problem is when the tank is empty the gauge can still read between E and 1/4 full. Fill the tank, then on level ground remove the gauge and look at the back. You will either see two slots in holes, or two cork plugs in holes. Remove the cork plugs to see the two slots. Use the one on the F side of the gauge to adjust the F reading and vice-versa. The metal with the slot in is only thin, and it can be stiff, so you need to use a full-width screwdriver or you risk 'rounding-out' the slots to holes. Twist the slotted plate to get an F reading.

Next drive your car to run the fuel down, then carry a spare gallon. Again in my experience, the gauge stops moving down before the fuel has run out, so this is the point to start watching closely and listening for the fuel pump chattering, which means the tank is effectively empty. At that point you have a choice. Either adjust the gauge to show E, add your spare gallon, then go and find a filling station. Or do what I did and add the spare gallon before adjusting the gauge, so you then have a psychological 'reserve'.
Paul Hunt 2

Mine does this but ius reliable and repeatable and I prefer the effective magnification on fuel remaining as you get towards empty, and yes it happened when the old sender was replaced in about 1997.
Stan Best

This thread was discussed between 04/10/2007 and 05/10/2007

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