Fuel Gauge issue
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Senior User
Joined: Oct 2015
Posts: 413
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From: Yakima, WA
Fuel Gauge issue
I have a 1948 Ford F1 that I have switched to 12V. All gauges, lights, and electronics work. My issue is that when I turn the key to the on position the fuel gauge pegs itself to the “full” reading. I have a new EZ wiring harness, Runtz, and sending unit. Anyone have any tips of where to start this chase?grounding? Anything I need to do to prep sending unit? Thanks for any help
More Turbo
Joined: Sep 2020
Posts: 577
Likes: 175
From: Thompsons Station, TN
I had the same problem. Turns out the “new” sending unit was bad. Pulled it out and checked the ohms. It should read from ten (10) to one hundred (100) as you rotate the arm. My first one didn’t come close. Sent it back. Checked the replacement before installing; it was fine. Try not to buy “made in China”. My latest was made in Taiwan. Couldn’t find US made.
Mountain Pass
Joined: Nov 2015
Posts: 189
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From: South Jersey
Unless you have a wiring issue and If are satisfied with “close enough” readings the new sender will work. If you want it to work like it should look and be reliable, for a OEM gas tank sender unit. They appear on E Bay occasionally. The new sender units are not and never will be compatible with the original dash board gauges. No matter what the vendors say.
hope this helps,
tom
hope this helps,
tom
FTE Legend
Joined: Nov 2015
Posts: 30,895
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From: Angier, NC
If you pull the wire off the sender does it still peg at full?
If so then you have an issue with the wiring from gauge to sender.
If the gauge does not move with the wire off the sender then it is a sender issue.
Dave ----
If so then you have an issue with the wiring from gauge to sender.
If the gauge does not move with the wire off the sender then it is a sender issue.
Dave ----
Parts Nerd Extraordinaire
Joined: Sep 2010
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From: Western NY
Stock sending units and gauges for your truck do not work on an ohms/resistance model that most cars and aftermarket components use. Instead, The stock units uses the The King-Seeley principle where the sending units supply a full 6V through the heater wire in the gauge in the form of a square wave with the duration of the "on" being the variable determining the gauge reading. The longer the duration, the more fuel in the tank. It is this full 6v of current which heats the bi-metallic strip in the stock gauge that causes the gauge to read via a small gear train (that has some adjustability). As stated before, most after market sending units are simply a variable resistor which sends a constant voltage to the gauge, lessening that voltage as the fuel level goes down. Therefore, the sending units signal doesn't heat the bimetallic strip in the stock gauge in a meaningful way. Unfortunately, the calibration of the resistance/ohm after-market sending units and the stock gauges don't match up very well due to the differences in the principle of the signal.
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Fleet Mechanic
Joined: Jun 2020
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From: Hillsborough NJ
Stock sending units and gauges for your truck do not work on an ohms/resistance model that most cars and aftermarket components use. Instead, The stock units uses the The King-Sealy principle where the sending units supply a full 6V through the heater wire in the gauge in the form of a square wave with the duration of the "on" being the variable determining the gauge reading. The longer the duration, the more fuel in the tank. It is this full 6v of current which heats the bi-metallic strip in the stock gauge that causes the gauge to read via a small gear train (that has some adjustability). As stated before, most after market sending units are simply a variable resistor which sends a constant voltage to the gauge, lessening that voltage as the fuel level goes down. Therefore, the sending units signal doesn't heat the bimetallic strip in the stock gauge in a meaningful way. Unfortunately, the calibration of the resistance/ohm after-market sending units and the stock gauges don't match up very well due to the differences in the principle of the signal.
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Parts Nerd Extraordinaire
Joined: Sep 2010
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From: Western NY
The way I test sending units is to FIRST test/verify the gauge using the D cell method described in the shop manual, and then connect the sending unit to the just tested gauge.
More Turbo
Joined: Sep 2011
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Hi I ran into the same problem with my gas gauge. I ran a 6 volt sender with a runtz voltage reducer to a 6 volt gauge this did nothing. The gauge always pegged full. I tested it and checked ground and checked that the fuel sender swung freely. I used the d cell battery test also. But my gauge moved but wouldn't do it in the tank. Finally I bought a 12 volt gauge and sending unit from Mid Fifty. Here is the rub the fuel sender was bad from the get go. I had to send it back and get another one. Finally I got it all to work. A little advice the end that bolts into the plastic end on the sending unit put a bend in it to form a l shape so it won't slip off and fall off the sender.
Hope all goes welll
Jerry
Hope all goes welll
Jerry
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Senior User
Joined: Oct 2015
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From: Yakima, WA
Pulled out the sending unit.
1. Removed ground wire from tab and attached sending wire on stud, turned key on - pegged at empty
2. Attached ground wire to tab, removed sending wire from stud, turned key on - pegged at empty
3. Attached ground wire to tab, attached sending wire to to stud, turned key on - pegged at full
i am going to assume from all 3 of these tests that I have a bad brand new sending unit.
1. Removed ground wire from tab and attached sending wire on stud, turned key on - pegged at empty
2. Attached ground wire to tab, removed sending wire from stud, turned key on - pegged at empty
3. Attached ground wire to tab, attached sending wire to to stud, turned key on - pegged at full
i am going to assume from all 3 of these tests that I have a bad brand new sending unit.
Parts Nerd Extraordinaire
Joined: Sep 2010
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From: Western NY
I do not know of any BRAND NEW/Aftermarket sending units that use the K-S principle signal that stock gauge requires.
Parts Nerd Extraordinaire
Joined: Sep 2010
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From: Western NY
You need a KS sending unit to match your KS gauge. That's the first problem.
The second problem is as you convert it to 12 volts which will require a proper reducer. I do not know if all reducers are compatible with the KS signal.
Third if you were not careful with your voltage conversion, I have seen many stock KS gauges burn up or become so uncalibrated when inadvertently fed with a 12-volt system. A D cell batter test as outlined in the Ford service manual should be able to validate both the halfway and full readings of the gauge ensuring that it is in spec.