1957 Ford gas gauge not working.

[57jake]

Gas gauge needle shows full tank all the time with ignition on. With ignition on and off needle moves freely up and down full scale. New tank sending unit tests good.

Disconnected the wire at the sending unit. Tested sender disconnected gauge wire to ground with ohm meter and it reads 1or 2 ohms, shorted.

Replaced the old wire from gauge to the sender with a new wire. Now the gas gauge reads about 5/8 full all the time. Disconnected the wire from the sending unit, and tested again with ohm meter to ground and the meter reads 400 ohms.

Lyle

[Ford blue blood]

I am going to assume the temp gauge is working OK? If so both the temp and fuel gauge are fed power from the same source. Lift the sender wire off the sender and turn on the ignition switch to run. The fuel gauge and the temp gauge should both read zero (low gas and temp). Next measure the voltage at the wire in the trunk with the sender still disconnected. Should be a pulsing reading if you have a good digital volt meter or just about 5 - 7 volts with an old analog meter. Next with the help of a friend momentarily ground the lead to the trunk floor, the fuel gauge should start moving toward full. If this happens your gauge, wire and power source are good. Next is the sender, it should provide a variable resistance starting high on empty and getting lower as the tanks fills. if you know it is good check to make sure your gas tank is grounded.

[57jake]

Bill,

All these tests check good.

The sending unit is new and provides variable resistance with an ohm meter.

Pulsing reading is 5-7 volts with an analog meter.

Tank is grounded.

Fuel gauge moves toward full when sender wire is grounded.

Lyle

[SSsssteamer]

I visited '57 Jake today. I tested his tank's new sending unit. First obvious thing was that the sending unit was not capable of giving a full tank reading. The best that it would show was half of a tank. The sending unit in the full tank position still showed quite a bit of resistance with an ohm meter. The other tank sending units that I have worked with on the early V 8 Fords, always showed zero ohms resistance in the full tank position. When 57 Jake's fuel guage wire is touched to ground, the fuel gauge would show full. On the 1957 Ford, how many Ohms resistance can be expected in the sending unit in the full tank position? 57 Jake has misplaced his tank's old sending unit, so we couldn't get any information off of that one.

[SSsssteamer]

I forgot to add that 57Jake's fuel tank has a good ground and that the wire to the sending unit was grounded to the tank at the sending unit to get the full tank reading. The new sending unit has a too high of a resistance to produce a full tank reading. I suspect that the new sending unit is incorrect for the car. Even the gasket that they sent with the sending unit is about a 1/2" too large of diameter. Any likely chance that the gas gauge has changed its calibration and is now requiring more voltage for a full tank reading?

[Ford blue blood]

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Nope, given the sending unit does not read a low resistance when full indicates it is the incorrect unit. The temp gauge and fuel gauge are simple current meters. The regulated voltage provides a consistant source, the sender provides the variable resistance and the meter deflects according to the amount of resulting current. He needs to get the correct sending unit.

[Frankenstein57]

Good stuff Bill

[57jake]

Thanks for the help Bill. I ordered another sender.
Lyle

[Ford blue blood]

Lyle any up date?

[SSsssteamer]

Dear Ford Blue, I asked Lyle about his fuel gauge. He says that he has received his new sending unit but he has been overloaded with honey do's around his home. He will get to the sending unit as soon as his other "do me first" projects are caught up.

[Ford blue blood]

Yup, well familiar with that deal, got to keep the other half happy or there is just no fun to be had!

[57jake]

Hi Ford Blue,

I received my new sender and it looks just like the other one I have. Testing it with a Fluke 75 meter it reads E 95 ohms. F 10 ohms. The other sender reads E 118 ohms and F 20 ohms.

When I move the float up and down, and testeing it with the ohm meter, the meter reads pretty steady on the new one. When testing the other sender, (E 118, F 20,) the ohms reading was not steady and would jump around some.

So I think I found my problem. I won't realy know until I drive my car. Now the tank is full and the gauge reads full.

Thanks for the help. This forum is great. Now it's back to more honey do projects.

Lyle

[Ford blue blood]

Excellent!