77 f250 ranger w 351m. I put in a new tank with new float/sending unit. Fuel gauge still wont work. If i unplug the pigtail at the tank the gauge will drop below empty. When it is plugged in the gauge just sits at empty. I tested the ground and that seems fine. Any suggestions?

 

What specifically was done to test the ground? The point at which the sending unit grounds and the engine block need to be at the same potential.

 

How much gas do you have in the new tank ? Start with the easy fix and remove the ground from the frame and clean it up or replace the eyelet and use a new self tapping screw and sand the frame where your going to put it. And if that don't fix it and you have the bed off just take the sending unit out and lift up the float and see if the gauge moves. If not then check the sender with an ohm meter set on 200. With the float down it should read about 15 ohms with the float up it should read about 160 ohms.

 

I do have access to the sending unit but it was brand new. If i lift the arm then the gauge should read full right? I took the ground off and jumped it to a power supply on the ground side. The ground on the truck was new and i did sand the ground location and used a brand new screw for it also. The gauge has not worked since i got the truck. I was thinking maybe the wire that goes from the tank to the gauge maybe just to weak from cracks and what not. The wire is pretty frail so i was thinking about rewiring it.

 

Yep, float lifted up should move gauge to full. Even though it's new I would still check the ohms at the sending unit to eliminate it as the problem and make sure the float arm goes up and down without binding, new doesn't always mean it's good. If that doesn't work then rewire it, just use butt connectors with shrink tubing, NAPA has some good ones. Still no go, bad gauge.

 

You said before to set the ohm meter to 200. How exactly would you check the ohms @ the sending unit? One lead of the Ohm meter to each wire? This is a 2 wire sending unit correct?

 

Yes it is 2 wire. One is ground the other is the wire to the gauge.

 

Yea, just put one probe on each terminal on the sending unit or unplug the connector on the frame, if the tank and bed are on the truck, and stick the probe into the wire in the socket going to the tank and the other to ground. A sending unit is nothing more than a variable resistor (rheostat) and the fuel gauge is an ohm meter.

 

So i need a new fuel gauge as it would turn out. Anyone have one they want to sell?

 

Ground out the sending unit wire on the frame and the gauge should peg full, that's how you test the guage.

Josh

 

By any chance did someone install an aftermarket gauge?

 

No it is a stock gauge. I tried groundng it out and it does nothing.

 

I thinks someone else had a problem like this before, They suggested flipped over or flip the float mechanism. I think they almost go in both ways. Not sure if that helped at all

 

So tonight i said the hell with it and i rewired the gauge just to see what would happen. Now it works just fine. The wire i pulled out and replaced didnt look "that" bad but hey it works now so i dont care.

 

COOL, I bet that is a big relief