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The new gasoline additives are indeed hard on some of the components in the fuel systems of our old cars, but the only damage I am aware of is to rubber parts that have not been updated to modern materials. These parts are found in the flexible fuel lines, the fuel pump, and the carburetor. There are no such parts in the fuel sender, unless it was a repaired unit which happened to have had a leaky float in the past, and said float had been repaired with some rubber compound – a very unlikely scenario, in my opinion.
A. The first step is to verify that the problem is the sender itself:
1. Measure the resistance from the sender output wire to the tank metal, to see if you get a reading that makes sense. With an empty tank, the reading should be above 50 ohms, and up to 100 Ohms. With the tank full, the reading should be between 0 and 10 Ohms. If this is what you read, there is nothing wrong with the sender. If the reading does not fall within these limits, or if it does not change as you change the fuel level, the sender has to come out for inspection.
2a. If the float is a solid cork or plastic float, forget the above – it’s OK.
3. If the float arm will move freely, monitor the Ohms reading as you move the arm – it should change over the above stated range. If it does, smoothly, the sender is OK and your problem is elsewhere. If it jumps, or the reading goes out of range at some positions, the sender is worn out. These can be repaired, but you’re probably better off to find another one that works. These should not wear out in 20 years or so of normal use, but of course that’s only an estimate. If it is worn out, and you want to try to rejuvenate it, it is a laughably simple device – take it apart and study it, you’ll see where the problem is right away, most likely – the wire wound rheostat winding will have broken or lost contact with the ground terminal, or the moving contact will have lost contact with the wire – there are really only two failure modes.
B. If the sender checks out OK, but the gauge still doesn’t work, verify that the wire that goes to the sender shows a pulsing voltage signal on it when your key is on. If your car is still 6 volts, the voltage should be jumping from 0 to 6 volts about once per second or so. If your car is 12 volts, the same thing happens, but the meter will jump higher regularly. The value doesn’t matter, if you see the varying voltage, your instrument regulator and all your wiring is OK. If you don’t see the pulsing voltage, your problem is electrical, probably in the wire coming from the dash indicator back to the tank – get out your shop manual and trace the wire. The most likely place for problems is right at the dash indicator – inspect that connection very carefully. Turn on the key and make sure you see the pulsing voltage there. If you don’t and your other gauges work OK, the problem is in your dash wiring.
If the above all checks out, the problem is most likely that your gas tank ground wire is missing, or making poor contact. Add a wire to one of the mounting bolts and make sure that it has clean bright bare metal contact both to the metal of the tank and to the car’s chassis. One of those steps will fix your sender problems.
Dick Benjamin
From:
mailing-list-owner@xxxxxxxxxxxxxxxx
[mailto:mailing-list-owner@xxxxxxxxxxxxxxxx] On
Behalf Of DONALDDICKINSOND@xxxxxx
Two years ago I bought a NOS unit for over $100 and it
lasted one year. I have been told two things about this sending unit
which I would like to have confirmed (or rebutted): |
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