Fuel Gauge not working

[boss]

I recently purchased a 1975 Bronco and the fuel gauge would not move. I cleaned the ground connection and the gauge will move just beyond E and then settle back just below E. Is it possible the ground is still not good enough to operate the fuel gauge properly or do have an other issue. The fuel tank has about 4 gals. of fuel.

 

[dao1980]

My fuel gauge and sending unit have had some crazy times together.
Here are a few things I've run into tinkering with them.

1: Little voltage regulator on the back of the gauge cluster was old and grumpy

2: The actual little fuel gauge pod was equally as old and almost as grumpy

3: When I went to fuel injection I cut 4" from the forward-side bottom and 3" from the forward-side top of my 24million gallon tank to give my rear axle a little breathing room, and did the factory ford fuel pump/sending unit in the tank to run the SEFI.
I didn't bend the little float arm just right (the first three tries) and even though I had the gauge and the fuel indicator pod seemingly happy, it still wouldn't read correctly.
It showed about 1/2 tank at full and I could drive it on empty for weeks before I really needed fuel.

These are just the three things I ran into.
I'm sure the folks here can offer much more in depth advice on trouble shooting it.

I know it stinks driving around wondering "how far can I go..." or "is there any gas left??"

 

[70_Steve]

I recently purchased a 1975 Bronco and the fuel gauge would not move. I cleaned the ground connection and the gauge will move just beyond E and then settle back just below E. Is it possible the ground is still not good enough to operate the fuel gauge properly or do have an other issue. The fuel tank has about 4 gals. of fuel.

Yes, it's possible the ground isn't sufficient. On these old Bronco's, the ONLY thing that used the frame for a ground was the fuel level sending unit. But, as far as I know, there was not a specific frame ground connection back to the battery.

The oil pressure, water temp, and fuel level gauges are all powered by an Instrument Voltage Regulator (IVR) mounted on the back of the gauge cluster. The output of the IVR is a pulsed voltage, and is daisy-chained to one side of all three gauges at the cluster. The other side of all three gauges goes to it's respective sending unit, with the possible exception of the fuel level, which may go to a dash switch to allow switching the gauge from the main tank sending unit to an auxiliary tank sending unit, if it came with one.

The sending units all change resistance, in the range of ~73 ohms at 0% and ~10 ohms at 100%. A quick check of the circuit operation would be to unplug the wire at the sending unit and verify the gauge goes below 0%. Then ground that wire, and verify the gauge goes above 100%. In your case, grounding that wire to the frame may not be the best check, until you verify or install a dedicated frame ground.

A good grounding scheme will have the negative battery cable bolted to the engine block, since the largest current draw on the Bronco is the starter. I've found a convenient spot right behind the stock alternator. Then, using the engine block as a collection point, install a ground strap/cable to the body. Another convenient spot is from the rear of the intake manifold to the firewall. Lots of extra bolt thread holes on the rear of the intake, without disturbing the intake manifold bolts. To provide my frame ground, I used the same bolt location on the block as my negative battery cable, and ran a ground strap to the frame.

 

[savage]

70_Steve ,can you just run a ground strap directly of the neg of the battery to the frame?

 

[70_Steve]

70_Steve ,can you just run a ground strap directly of the neg of the battery to the frame?

Yeah that will work. For me it was more convenient to use the same bolt on the block that attached my negative battery cable.

However you do it, the objective is to have the engine, body and frame all grounded back to the battery negative terminal.

 

[savage]

Thanks ,I going to ground it like you did.

 

[Authorizedcc]

My fuel gauge wasn't working, turn out to be the float on the sending unit was bad.

 

[broncobilly72]

you can test your gauge with a nine volt battery with two wires attached and alligator clips on the end. If the gauge is good it will respond to the nine volts.... and oh yeah ,do this test with the key off. If nthe gauge is good, then it is more than likely the sending unit float is shot.

 

[boss]

Dose it matter which connection from the 9 volt battery goes to which post of the fuel gauge?( + or - )

 

[asinor]

Also, old cracked, loose, broken corroded wiring / connectors from the sending unit.

 

[asinor]

Check the continuity of the wires. Check the resistance of the sending unit at the tank.

 

[67RT]

My issue was the gas tank selector switch. I took the wires from the senders off of the selector and jumped directly to the gauge. It then worked..

As said, check resistance from senders and also across middle and side tabs of selector (a pain to get to). As yo switch selector resistance should go from infinite to zero depending on where you are hooked up..

 

[69red]

when my gauge don't work, the problem is the same as 67RT said.

I just have to wiggle the wires on the back of the selector on the dash and they work again for a few years.

its on my list of things to fix...

 

[dmplatt]

I have a bit of wonkiness with my gauge and wiggling the wires just changed the specifics so I'm guessing I have some bad connections back there. If I take the clip and bezel off the front will it slide out the back of the dash pretty easily or is there a better way to get to those wires?