How do you test a fuel sending unit?

[Bundy]

I have no idea if my sending unit on my NWP 12 gal aux tank works... is there a way to test it to see if it works or do I need to pull it out and visually inspect it?

 

[gddyap]

Measure the resistance across the terminals and see if it falls within the specified range. Is there any gas in the tank?

 

[gearida]

Ground one side of the sending unit and see if the gauge then pegs to full.

 

[fungus]

Great topic! Mine worked for awhile and now pegs to full when I flip the switch. What gives? I've redone the ground to frame a couple times with no results...

 

[Bundy]

no gas in the tank and nothing is installed- does anyone happen to know what the resistance should be? if not, i will try hooking up the gauge and grounding the sending unit... i mean i don't even know if the gauge works! ;D

 

[chuck]

~10= full,~73= empty

 

[nutter3]

10-70 Ohm

 

[nutter3]

Damn, Chuck beat me to it;D

 

[Viperwolf1]

Great topic! Mine worked for awhile and now pegs to full when I flip the switch. What gives? I've redone the ground to frame a couple times with no results...

It pegs because there's too much current going through the circuit. A better ground will not fix the problem. You need to figure out where that current is going. Either the sender is shorted, float is stuck in the up position, or the sender wire is shorted to ground before it gets to the tank.

 

[chuck]

yah, what viperwolf1 said

 

[Bundy]

great info guys! if my tank is empty, is there a way to see if my current gauge works besides filling up the tank?

Also, how can i run two sending units into one gauge?

 

[Viperwolf1]

great info guys! if my tank is empty, is there a way to see if my current gauge works besides filling up the tank?

Also, how can i run two sending units into one gauge?

You can test the gauge (not the sender) by grounding the sender wire then turning the key on momentarily. If you want to test the sender you should remove it.

You only need a double throw switch to run two senders to a single gauge.

 

[Bundy]

You can test the gauge (not the sender) by grounding the sender wire then turning the key on momentarily. If you want to test the sender you should remove it.

You only need a double throw switch to run two senders to a single gauge.

Viperwolf, I don't have any wiring in the bronco currently so turning the key is a ways out... can i do that test with the battery? I have to ground the battery in order to use it, right?

 

[Viperwolf1]

Viperwolf, I don't have any wiring in the bronco currently so turning the key is a ways out... can i do that test with the battery? I have to ground the battery in order to use it, right?

That complicates things. The gauge doesn't operate on 12V. It operates on the fluctuating voltage provided by the instrument voltage regulator. An alternate method is to just use an ohmmeter of the gauge terminals. It should be 10-14 ohms.

 

[fungus]

It pegs because there's too much current going through the circuit. A better ground will not fix the problem. You need to figure out where that current is going. Either the sender is shorted, float is stuck in the up position, or the sender wire is shorted to ground before it gets to the tank.

Thanks! I'll have to pull the sender again and check it out. Ran a new wire from the switch to tank this last go round so it's not the problem. I might have it pulled up too tight to the body and grounding out on the floorboard too...

 

[oleguy74]

pm sent to bundy.

 

[BCH BRCO]

Not to hi-jack, but what can you do to fix a sending unit that says I have a quarter tank of gas but it only has about a gallon or less in it??

 

[oleguy74]

take it out and put an ohmmeter accross the terminals.raise and lower it.if it goes between 10 and 73 ohms its good.may have to bend float rod.

 

[Viperwolf1]

Not to hi-jack, but what can you do to fix a sending unit that says I have a quarter tank of gas but it only has about a gallon or less in it??

If it is working otherwise then you need to change the level of the float to accurately indicate whats in the tank. That means bend the float arm up to about where 1/4 tank of fuel would be. This will have an affect on the full reading also. It takes some trial and error to get both ends of the scale exactly right. I've had to bend and extend float arms to do that.