I have an 89 F250 w/351 and dual tanks. The tanks draw gas fine, but if the switch is set for the front tank, the lowest it shows is half a tank. Even if the tank is empty and you add a couple of gallons of gas, the fuel level gauge will rise. The rear fuel gauge works fine. I've read conflicting information about how the gas gauges work on these trucks, so any information would be helpful. The strangest thing to me is that my initial reaction was a stuck sender in the tank, but if the tank is empty and you add 2 gallons, the fuel level shouldn't raise high enough to affect the sending unit.
Thoughts?

 

its prob a worn sending unit. im not familiar with the ins and outs of the common dual system problems, but since its registering, just not accurately, it seems to me that the rest of the system is in tact. the gauge is receiving the signal from the sending unit, its just a faulty one.

 

That was my first reaction, but like I said, if it was a stuck sending unit then a small amount of gas wouldn't reach the float to change the fuel gauge reading. I may be wrong about that, but it seems to me to be a logical conclusion.

 

its prob not stuck, or if it does get stuck its mid-range (unlikely). so, that leaves a faulty unit. it could be reading and sending below half tank, but faulty after.

 

I guess I'll give the switch a good cleaning. After that, it's on to percussive troubleshooting.
Thanks!

 

you really might be chasing problems that aren't worth chasing. cleaning the switch when its functioning isn't going to do anything. perhaps be happy its functioning, and just run the tank w/ faulty sending unit by mileage.

 

The fuel gage works off of resistance like a multimeter. I do not know the scale for the fords, but for instance on most GM cars 0 ohms is full and 90 ohms is empty. So probably have a loose or corroded connection some where in the sending unit that is not reading correctly. You can eliminate the gage and front connections as being bad because the rer tank reads good you said. Unfortunately you may need to pull the sending unit to check the connections

Matt

 

Yeah, I was in denial. I knew that somehow I was going to have to pull the tank. Truthfully, both tanks probably need to be cleaned out. Right now, I'm just concentrating on getting it to pass inspection.