is it a gauge problem, or is it a sending unit problem?

[Knuckledragger]

I told you all about the truck quitting on the freeway a week ago. Now that I have fixed that problem, I have another.

I dropped the rear tank (what fun!) to get out the rear sending unit and replaced some of the parts that were missing since I could not buy anything but a float from Ford. I tested the unit and got resistance but could not get an accurate or repeatable reading. It was better than the nothing that I was getting before, so I made a nice replacement pickup to take the place of the bits and pieces that were in the bottom of the tank (see photos).

Replaced the front tank sending unit with one from the junkyard (out of a diesel, no less) that had been checked for resistance, getting 22 ohms at empty, like the book says.

Got both reinstalled and STILL no reading on the gauge in the dash. Dang. So, I'll be trying to check the gauge for it's condition and whether or not it works. I hate driving around not knowing how much fuel I have. But now I at least have a quarter tank more than before, since both pickups were disintegrated.

 

[icanfixall]

Hello Mike.... Any chance you opened up the reostat part of the sending unit and looked at the printed circut board for worn thru wires. These gauges wear out that board and then they work when they want to. They usually will never tell the truth either. I have seen lots of these sending units in the yards all taken out of the tanks and opened up. This is just another really crappy ford only idea. If you could remove the front tank sending unit and make it show full or mt maybe that will point you in the dash or sending unit direction...

 

[94f450sd]

another thing i have found to cause your problem is bad grounds in the harness,switch over valve or the dash switch

 

[Knuckledragger]

Gary,

Yeah, I took everything apart. the rear tank did not have the little brass conductor that wipes the circuit board. Wasn't in the tank, nowhere. I know what you mean about the wires being worn off, but it seemed to get readings everywhere I tested. Looks as if I need to test every wire up to the gauge.

One of the floats was completely filled, but did not drain out after I took it out. the other had a hole in it. At first, I thought it was only a matter of changing floats, but no dice.