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Offline caravan3921

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Gas gauge
« on: June 05, 2021, 12:22:43 PM »
The gas gauge appears to be acting unreliable lately.
Seems to always be stuck at 3/4 full when it should be going down.
Filled it to full yesterday and drove it home 2 blocks away and it was at 3/4.
What would the experts do?
Thanks!

Offline Wittsend

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Re: Gas gauge
« Reply #1 on: June 05, 2021, 02:54:57 PM »
Likely it is a sinking float, or there is varnish on the sender resistor. I don't know if the floats are available but it isn't too difficult to remove one (the float itself and a length of the arm it attaches too) from a junk yard car and adapt (solder) it to the existing arm. And by that I mean solder a portion of  metal arm that holds the new-er float to the existing arm, not solder the float itself  - which today is likely plastic.

Varnish can be removed often by scraping it but be careful not to damage the wound wires on the resistor.

Offline oldandcrotchety

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Re: Gas gauge
« Reply #2 on: June 05, 2021, 05:10:05 PM »
I don't know if Pintos used them, but a lot of the old fords had a resistor behind the fuel gauge that would go bad.  When it does go bad, the gauge will read 3/4 tank when it is really full, and then run out of gas with the gauge showing 1/4.  I had that happen on my '64 ford pickup and also on a 1970.  They are real easy to replace, but as I said, I have no idea if were used on the Pintos.

Offline Mattb

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Re: Gas gauge
« Reply #3 on: June 05, 2021, 06:27:55 PM »
Based on the picture of you car looks like you have a 77 or a 78.  For those years in my experience the Pinto and Mustang II used the same sending units. If you go to Spectra’s website and look at their e catalogue they list sending units for the Mustang  II.  You would probably want the FG 179B( I believe that is what I used). It has a second pipe for a return line. The V8 Mustang II  did not have a return line. It appears the 179B is not available right now. The 1976 cars use a FG 178B which looks like the same dimensions but has a slightly different Ohm range( 85-10 vs75-10).  When I pulled the tank we actually put in a new tank as well along with new rubber parts. Just something to consider. Best wishes.

Offline LongTimeFordMan

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Re: Gas gauge
« Reply #4 on: June 05, 2021, 08:57:01 PM »
i think the "resistor is actually a voltage regulator to regulate the instrument voltage at 6 volts.

the oem ones had a system like a turn signal flasher that turned and off. there are also new style electronic ones avaialble.

but your problem seems like it might be the sending unit.

you can also test the resistance of the sending unit.. it should range from 10 ohms full to to.70 or 80 ohms empty (see the above post ) as the level in the tank

if the.resistance of the sending unit changes with the level, the problem could be the voltage regulator.

inpostes a post about building and calibrating an electronic regulator here awhile back.
Red 1973 pinto wagon DD, SoCal desert car, Factory 4 speed, 3.40 gears, Stock engine, 14" rims and tires, 60 K original miles