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MPI fuel gauge inaccuraccies (12 replies)

7 years ago
jackbilly1 7 years ago

MPI fuel gauge inaccuraccies

7 years ago
MGMiniman 7 years ago

I have calibrated all of the fuel gauges/sender units on all of the Minis I have had.
Let's face it they are notoriously inaccurate. The most accurate gauge is a dip-stick!
I have carried out calibration on carb cars but never on a Spi or Mpi but I suspect this method will still work.
Before you do this I must caution that you will be playing about with a highly inflammable liquid and this must be carried out in a well ventilated out of doors environment and I accept absolutely no responsibility for any mishaps. You do this at your own risk.

However the best way of calibrating the gauge is to run the tank out or empty it.
Then put the amount of fuel you consider to be your "reserve" in the tank. I use 1 gallon.
Switch on the ignition and read the gauge. Just above zero - leave it alone.
It may be wise to get a new sender unit seal before you dismantle the tank/sender unit.
If this is not the case then carefully remove the sender unit from the tank. The fuel level will be below the sender unit mounting hole. Stuff a rag in the hole to reduce the fuel fumes coming out of the hole. Absolutely no smoking of course and make sure you turn off the ignition when connecting or reconnecting the wiring to ensure there are no sparks.
Check the plastic float is intact and there is no fuel inside it. I have seen these fill with fuel and of course then the gauge will not work.
Reconnect the wiring turn on the ignition and observe the gauge. Move the arm to the top or full position and make sure the gauge actually reads full. On the units I have worked on there is a small screw that allows you to move the arm on the shaft to achieve a full reading. Move the arm to the lower position and make sure that the gauge reads empty.
Only early cars will have gauges that react quickly. Cars after around 1964/65 will have hot wire type gauges that take a little while to react to change of the float position so give the gauge time to settle.
Put the sender unit back in the tank, reconnect the wiring to the sender unit and observe gauge reading.
If it reads just above empty then that's OK. If not bend the float arm appropriately to get a reading on the gauge to show just above empty. Make sure that when you replace the sender unit that it is sealed to the tank and check when the tank is next filled. Especially with injection cars.
I find that when you get down to the empty reading you should have enough fuel to reach a filling station.
Most modern cars have a warning light that gives you about 30miles reserve.
I hope this helps but again I caution take extreme care when messing with open tanks of fuel.

Peter Laidler
7 years ago
Peter Laidler 7 years ago

Thanks for that miniman. A good simple way to cure the problem with loads of good tips and advice.

I wish there was a little tick box below each thread to add a named thanks.........

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