CJ fuel gauge testing?

[trailjeepman]

How do I test the fuel gauge on an 84 CJ7? New fuel sending unit and also new speedometer with fuel gauge. Gauge is showing empty even though the tank is full. Old gauge if hooked up shows full but way past full. Not sure what is going on.

 

[Tom@Hilltop_Machine]

Unplug the sending unit wire at the back of the jeep. Ground the wire coming from the gauge. It should move to full. If so then the gauge is good and so is the wire to that point. If it doesn't move then there is an issue with the gauge or wiring. On another note the plastic float in the sending unit doesnt like ethanol gas and will get soft and allow fuel to enter the float and then the float stops floating and sinks to the bottom and will show empty on your gauge even when your tank is full.

 

[Tom@Hilltop_Machine]

Also the speedo unit grounds through the dash. Since you replaced it make sure its seated good and there isn't dirt, old paint, and crud in between the dash and the unit.

 

[adman02]

John Strenk pretty much knows everything about Cj gauges. Check out his articles here.

 

[shawn]

Are you sure it's the correct gauge for the vehicle? Different vehicles do it different ways, but generally speaking, they change the resistance of the circuit with the sending unit, and the gauge tells you what the electrical resistance is.

An OEM CJ gauge should read empty at about 75 ohms, and full at 10 ohms. If you short the signal wire to +12V, the gauge should move toward full, then back to empty again when you disconnect it. Just don't hold it there for long, since the direct short could damage the gauge. If you have some resistors laying around, you could test it more thoroughly that way.

 

[shawn]

Merged the double posted thread 'cause it made me have deja vu....

 

[orange150]

A lot of the 'new' gauges are junk right out of the box. Search the John Strenk articles like @adman02 recommended and get to know your multimeter

 

[trailjeepman]

Thanks guys. Looks like the gauge is bad. Just ordered a replacement.

 

[orange150]

Thanks guys. Looks like the gauge is bad. Just ordered a replacement.

FWIW, Speedhut makes a full CJ set. That's going to be my route if/when I get that far with mine.

 

[rodney eppes]

Don't know about the 84, but older models like 79, got some crazy wiring. Two or more gauges are jumped/tied together, in a series. And if you touch 1 wrong wire, or ground or power 1 wrong, even a split second, that fuel gauge is Blown.