If the E is like our K, the gas gauge in the dash contains an electronic circuit to maintain a low, but constant, voltage. The K gauge generates a steady 5.0 Volt source which is used in conjunction with the variable resistance of the tank sending unit and a big external capacitor connected to the power input side to produce a steady fuel gauge needle. The 5.0 Volt source is also fed to the temperature gauge in the K dash so that it might also produce an accurate temperature gauge reading regardless of the changing system Voltage. If that constant voltage circuit is not working correctly, both the temperature gauge and gas gauge should be affected.
Jeff Carter and others certainly know more about this system than I, but you should be able to measure that 5.0 Volt source Voltage (”A”) with 12 Volts applied to the power input side (“I”) and a variable resistance placed between ground and the sensor connection (“S”) of the Fuel Gage.
The tank level sensor is essentially an insulator wound on the outside with resistance wire. A finger slides across the wire as fuel level varies and produces a variable resistance to ground. Over time, alignment of the finger and the proper tension to keep it engaged against the wire winding can vary so that the finger is not always in contact with some point on the wire.. I would think that the sliding finger should be able to scrape off any crud as the tank level waxes and wanes.
The other element of the circuit is the wiring from the tank level sensor and the gauge. As with all wiring, it is exposed to possible wear through increasingly brittle insulation and rubbing if not properly routed.. There are several connectors in its length. All can be problematic. The flange of the sensor must be connected to a good ground somehow. The lock ring connects the mounting flange to the tank (if not corroded) and the tank must then be grounded to the chassis. Running a ground wire from the sensor mounting flange to the frame helps guarantee the necessary good ground. My K has two printed circuit boards behind the instrument panel. Checking out a spare panel I have, I found that there is a bad connection between one of the pin connectors and the copper surface to which it is crimped. It does not appear to be soldered and a bad connection at the instrument panel connector/pin is another possible source of the problem.
Mechanically, the float must float. If brass, it must not leak or have gasoline inside it, if cork or foam, it must not become saturated. And, the bends in the float mounting wire must be proper to track tank level from full to empty.
Or, you can just fill up every 150 miles on the trip odometer. I probably have a problem now with my K as I have driven it 70 miles since the last fill and it still reads Full. And the temp gauge has stopped working.
Do keep us posted as to which element or elements of the system had failed and how the repair was implemented.
Thanks,
300K’ly,
Rich Barber
Brentwood, CA
Good Evening to Everyone Out There in 300 Land!!!
Well, the gas gauge on my 300E does not work! Now, I know it is not the
sending unit - had that rebuilt and it is in working order. It has to be
the gauge on the dashboard. However, before I try and go to the trouble of
removing it, how much of a pain is it, or does anyone have any tips on how
to proceed doing this. Then, once removed, does anyone have someone they
recommend to fix it? Symptoms of the problem: when the tank is less than
half full, it registers empty and when more than half full it registers full!
Thanks to everyone in advance who replies!
Sincerely,
Tom
Miami, Florida
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