Fuel gauge not working correctly

[Blue71]

New sender, new Centech wiring harness, etc a few years ago. Main fuel gauge worked a few days ago. Has 8+ gallons of fuel in tank. I turn the key on and the needle barely gets right at or just above empty ...turn key off and it goes below empty to resting position.

Things I've done:

Grounded out the fuel gauge on the cluster and it reads full.
Grounded out gauge at tank pigtail and it reads full.
Checked frame ground it's good.
Checked pigtail connectors and they are in good shape.
Ran two jumper wires from pigtail connectors to two connectors on sender and it reads full for some reason???

Any ideas? Bad sender? What should the sender be reading a meter if tank is almost full?

Thanks,

Blue71

 

[Viperwolf1]

Use an ohmmeter on the sender. 73 ohms is empty, 23 ohms is half tank, 10 ohms is full.

 

[Blue71]

Will do...headed back out there now. Thanks Viper. Also jumped the two orange wires under the dash to bypass the main/aux tank switch and I got nothing at all on the gauge

Blue 71

 

[Blue71]

I get 50.7 on my ohm meter on the main tank sender if I'm reading correctly. I just put 8 gals in and so I'm guessing there is 9.5 or so in the tank. I have a new aux tank sender that I tested by hooking it up to my pigtail and it seems to read full when arm is extended manually all the way , but reads almost empty at where half tank would be. Leads me to believe if I'd have filled the tank full I'd get a full reading with my current sender. Aux tank sender read 9.0 full and 80.1 empty..which sounds like it's working.


Hmmm

Blue71

 

[Viperwolf1]

Ohms matches up to what gauge is reading. Maybe the float arm needs to be tweaked to make it more accurate or maybe float is really a sink.

 

[mini73]

I'm am in the same situation now also. Just cleaned the main fuel tank this past weekend and replaced the fuel sender. I wasn't getting a reading so I jumped the 2 wires at the switch to by pass it since I only have the main tank in for now. I got it to go up and down while it was out and even once I put it it with about a 1/4 tank of fuel I still got the gauge to move. Went to the gas station and got some good gas to put in it to get it a 1/2 tank of gas. Not my fuel gauge barely gets off e.

 

[cbolt]

Voltage regulator on inst. cluster?

 

[mini73]

No. Rest of my gauges working good.

 

[Blue71]

Yep! The other gauges work properly as well.

Blue71

 

[Blue71]

Well fellas... I got it figured out. Pulled the sending unit and the float was full of gas. Must have a crack in it. Put a new float on it and I'm back in business. Hope this helps somebody in the future. Thanks guys ,

Blue71

 

[mini73]

Well fellas... I got it figured out. Pulled the sending unit and the float was full of gas. Must have a crack in it. Put a new float on it and I'm back in business. Hope this helps somebody in the future. Thanks guys ,

Blue71

I've been thinking this might be the problem also. Might check once I get the bronco out of the garage for the first time since buying it and also since I drained the tank now. Thanks for the update.

 

[clarrance]

This is the 3rd time I have heard about a brand new sending unit having a bad float in the past year. Sounds like there is a run of bad sending unit floats "floating" around out there.

 

[mini73]

Lol. Floating out there but not floating in the tank.

 

[IamHawk]

I have 2 brand new sending units in my 1975, and both tested fine before installation, but afterwards, I can't get either tank to read more than 1/2 a tank at best.
I have filled both tanks to the point of fuel in the neck, and I'll watch the gauge raise, then “skip” and then settle right around 1/2 a tank.
I'm gonna drain the rear and pull the sending unit to see if the float is bad. Both units came from atom's.