Fuel gauge problem's?

[nomad]

Please remind me. When the gauge reads full is that at maximum or minimum resistance. Appears my gauge has succumb to the third world roads I drive here in this good conservative state of South Dakota. Changing my suspention back to the softest I can come up with while I fix the gauge!

Kurt

 

[dklawson]

For Smiths gauge systems using the voltage stabilizer, the nominal values for fuel gauge sending units are: 270 Ohms = Empty, 33 Ohms = Full

Those are nominal values. Your sending unit may be different.

 

[nomad]

Thanks, Doug.
Should have mentioned that this is the earlier gauge but least resistance is at full for them too I imagine. Just hoping that a connection had shaken loose. Went from reading a tank almost empty to one reading almost full. Thought maybe my memory was at fault and trusted the gauge.....fortunately I did manage to coast up to a neighbors gas tank!

So if it was a dead short in the wiring it should read full but it only reads 3/4 so I suspect something's gone wrong with the sending unit. What do you think?

Kurt

 

[dklawson]

Sorry, I didn't realize you were dealing with an earlier car.

If this is the gauge system without the voltage stabilizer (skinny needle that can bounce all over the place) the resistance values are different from the later bimetallic gauges I mentioned above and the system is much more finicky.

For the magnetic gauges (w/o the stabilizer) the resistance range goes from nominally 10 Ohms = Empty to 80-90 Ohms = Full. This direction of resistance change is opposite that of the later bimetallic gauges I talked about in my first post. For a great explanation of that gauge system and how to tweak its calibration visit Barney Gaylord's MGA Guru website.

However, I do want to mention that with the magnetic gauges the fuel gauge itself MUST have a good ground connection or it won't read correctly. If during your work you disconnect any wires from the magnetic gauges note where each wire was attached. Unlike the bimetallic gauges, the wires have to be on the correct terminals (green to the gauge's "B" terminal, green/black to the gauge's "T" terminal... B for battery, T for tank). If you have a break inside the sending unit, if the tank or sending unit loses its ground, or if the green/black wire is cut/broken somewhere the gauge will read "beyond full"... not empty as you might expect.

 

[nomad]

Ah, should have thought of MGA Guru. So, as you mention, I could still have a wiring problem. Its a Mk3 Sprite late 64 BTW.
I'll see what Mr Gaylord has to say.

Kurt