Afternoon all! Hoping to make this an easy diagnostic by doing all the testing I can think of so you guys don’t have to walk me through the basics or have to make a wild guess lol!

So I’m working through some fuel gauge issues and looking for some insight.

Already done (necessary):
New grounds at sending units
New pigtails
New selector switch and wire ends

Tests:

First:
Both sending units appear to be newer and ohm out at 10(ish) ohms full and 80 ohms empty when tested on the bench.

Second:
Bench tested gas gauge with 9v battery and it full sweeps

Third:
Tested gauge while installed on truck with sending unit plugged in and dangling out of tank so I had full access to the float arm, put the float to full and the gauge pegs.

Fourth:
Bench tested ohms on senders, made a witness mark at 40 ohms (theoretical half tank) and it was exactly half sweep in the slot for the float arm on both senders. I see that as a good thing, I would assume the gauge wants to see around half the ohms at half tank?

Fifth:
Plugged each sender in at both tanks just to isolate any potential wiring issues, I had taped the float arms so they wouldn't move at the witness marks for 40 ohms (in theory half tank, and half sweep for the float arms). And what I found true for both senders, plugged in both tanks, with the float arm taped at the 40 ohm mark (half sweep of the float) I get just barely above the Empty line on the gauge.

So the issue is, driving around.. it’s on E pretty darn quick seeing how the sending unit (float) reaches halfway on it's sweep, essentially when the tank is half full, the gauge is on the line for E.

Call me a bonehead but what the heck am I overlooking?

Do I just need to bend the heck out of the float rods and play a guessing game to utilize the middle (40 ohm) to full (80 ohm) area of the senders? That seems really weird to only utilize half of the ohm/sweep spectrum of the senders or is there another issue like a bad gauge??

 

Sorry, I can't help you other than to say you're not alone. My main tank read empty when it's still about half full. My aux tank isn't that bad so I deal with it by running my main tank first and pretty much ignoring the gage. When I run out I know I still have the full aux tank with a (more-or-less) working gage.

 

Sorry all I got is... my sending unit does not have any wiring going to it at all, so I just top off the tank every time I hit the trail. So I have no good advice except check out these folks below. They are like early Bronco engineers with tons of advice/experience and years of knowledge.

Classic Bronco site: https://classicbroncos.com/forums/