I have a 1977 Bronco that I got last fall. I pulled the tank today to check out why the gauge wasn't reading right. The tank is a plastic tank and it looks like it has a newer sending unit in it also. I took the sending unit out and it reads 50ohms empty and about 50ohms full when I move the float up and down. I hooked it to the Bronco and moved the float out of the tank and the gauge reads right. When I put the tank back in with no gas in it the gauge reads about 3/4 tank. I put the gas in that I took out before I took it out and it shows full with about 7-8 gallons in it. It is the same as it was when I took it out.

Has anyone had this problem before? Anyone have any ideas on what the problem is? I would appreciate any help.

Steve

 

The simple diagnosis I have always heard is you take the wire off the sending unit from the harness and ground it. The the gas guage reads full you replace the sending unit. If the guage does not read full, you replace the guage.

 

Yeah, I have heard that before too, but like I said it worked fine out of the tank when I had it hooked to the Bronco. That is what has me stumped. It works fine out of the tank, but not in the tank.

Steve

 

Did you happen to shake the float to discover if there was gas inside? The float is made from 2 pieces of copper soldered together. Solder breaks down, gas seeps into float, float settles slowly to the bottom of the tank.

The float, sender gasket and the plastic mesh filter screen that slides over the end of the pickup tube are available separately from Ford. The float fits every Ford fuel sender, car & truck from 1957 thru 1979.


C0AZ-9202-B .. Fuel Sender Float

C0AF-9276-A .. Fuel Sender O Ring Gasket

D1AZ-9A011-A .. Plastic Mesh Filter Screen

 

That was one of the first things I checked after I got it out of the tank. There wasn't anything in the float. I think that the sender in an aftermarket unit though. I didn't see any Ford part numbers on it anywhere.

Maybe I should just buy another sender. They are like $50 from Bronco Graveyard. I think I will drop the tank again and check things out before I do that though. See if I missed something.

Steve

 

Just buy another sender. If it doesn't work in the tank, it doesn't work.
Make sure the gas guage reads full when the lead is grounded. Drive it with the line grounded for while and see if the guage still says full. What you are really looking for in that test is making sure there is not a bare spot on that wire to the sender in the harness that's messing with your reading.

 

I hadn't thought of there being a bad wire. I will try that. Thanks for the idea.

Steve

 

The Early Bronco gauges don't work off of 12 volts there is a resistor that drops the voltage to about 2.5 volts (I don't remember exactly). Having a good ground is extreamly important for the gauge to work corectly. I would run a wire to the sending unit from a very good ground to check to see if that is the reason the gauge works out of the tank and not when it is installed.

 

Ford fuel tank sending units have always come in cardboard boxes (since 1932), and for that reason have no part numbers on them. This is true for most Ford parts. If the parts are boxed, there's no number.

 

When I had it out of the tank though I had the factory harness plugged onto the sender just like it is in the tank. There is a resistor under the dash that the gauge runs through. I don't know if it could be bad maybe letting too much voltage through? I ran wires from the sender to a good ground and from the sender to the side of the gauge that the sender hooks to in order to eliminate any bad wiring. It still worked the same, so I am pretty sure the wiring is good.

Numberdummy, thanks for the info on the part numbers. Another reason I thought it was aftermarket is that it is chrome. All of the other Ford senders I have seen were like galvanized or zinc plated.

Steve

 

Where that wiring harness goes into the firewall there are three plugs. I think I know which plug it is but don't know which wire to ground. Anyone know the wire color? 86 F150

Thanks,

Chuck

 

Sorry, wrong forum. But I found it anyway. It's the two wire connector.