Voltage ??s - Fuel level sender from different years.

[FJsnoozer]

Does anyone know if the voltage is different between a 73-77 and the 79+ 22 gallon tank level sender.

I hooked the sender up for the first time last night and it shows 1/3 a tank when it is full. however, This is without a good ground connection. The ground seems to not make any difference at all in the reading.

Does anyone know if these years use different voltages? Since I have a 77 harness with a 79 tank, I may have to modify the sender and use the rod and float from the 79 and attach it to the 77 sender.

Or, these could both use the same resistance/ voltage and my sender is just bad, which is most likely the case.

 

[maingear]

FJ 1979+
The fuel gauge correlates to the voltage passing through the sending unit. There is a voltage regulator in the instrument cluster that feeds the fuel gauge so that nothing exciting happens in the tank.

if you think it is a ground, run a test ground from battery to sending unit's top and see if it is the ground (with the tank sealed shut in case of spark due to bad ground) gas needle should jump to a higher amount.

Sending unit in the tank is a variable resistor.
Full 14.9-19.1 Ohms (Arm up)
Half 35.5-44.5 (half)
Empty 113.5-126.5 (Arm down)

FYI- I have mixed/matched 12v sending units on military 24V systems with no problems (probably because they are all stepped down to the same voltage)

 

[Fast Eddy]

You're probably getting lucky with a ground from the body, through the tank and the screws that attach the top of the sending unit so you don't need the ground wire. Normally the tank is insulated by the rubber strips it sits on and the paint.

Hook up a potentiometer, such as a volume control to the lines and see if you can control your fuel gauge with it. Dial it down to empty, measure the ohms, dial it up to full, measure the ohms, then compare to maingear's readings to see if they are the same.

If your observation is correct and there are no other problems, then it sounds like your sending unit is reading something like 60-70 ohms at full. You need to figure out a voltage divider circuit to make the range match what you want. I can probably figure it out if you send me a PM after you get all the info. You may want to pull the sending unit so you don't have to wait until you use all the gas to figure it out. You could also inspect to be sure it's all connected internally. If the tab on the top can rotate any, it can break one of the variable resistor connections. I have a thread somewhere where I repaired mine and used some JB Weld to keep the tab from rotating.

 

[FJsnoozer]

I wil tinker with this soon. Until then, my 22 gallon tank gives me plenty piece of mine for cruising around town.

I will post back with my results when I can, but Wedding and honeymoon may delay this.


Thank you as usual guys.

 

[f1junky]

I need to know if anyone out there knows if a sending unit from a late '70's fuel tank will physically fit in my aftermarket rear fuel tank. The one I have needs to be rewound and I think it would be easier just to replace it with a new one. I can get a new one for a late'70's for just about $30.00 from Cruiser Corp. The problem is they don't have the size specs on it. I am not worried about the resistance as I will get the proper gauge for it.

 

[bj40green]

Fuel senders:
Sept. '71 - Dec. '78 83320-60050


Jan. '79 - April '86 83320-60051


The differences are:
83320-60050 Has 1 prong. Is for tank under pas. seat. Arm/rod is short.
----> The sender needs a good ground to the body!
There should be a ground wire (White/Black) with a ring terminal connected to one of the sender housing mounting screws.

8332060051 Has 2 prongs. Is for tank under the body. Arm/rod is long(er).
----> Ground problem is solved with this unit.

Electrically they are equal.


In my thread in post #7 you'll find all the info you need; -► Clusters, Gauges & Odo meters

As said before by maingear.... there is a build-in Voltage Regulator in the FUEL gauge. This one provides +/- 7V for the FUEL sender and the TEMP sender. If your TEMP reading is normal it means that the VR is doing it's job. This 7V is actually the average between 0 and 14V when the truck is running. This is done by the VR by switching on and off in a cyclus. If you try to read that on a digital multi meter you'see only rolling numbers. If you try to read this with a analog multi meter you'll see a sweeping needle between 3 and 11Volts (the average is in the middle so 7V).

Rudi

 

[f1junky]

Do you by chance know the difference's in length? Or better put, do you know the dimensions of the two from the bottom of the mounting plate to the fully extended and "full" positions?

 

[bj40green]

Do you by chance know the difference's in length? Or better put, do you know the dimensions of the two from the bottom of the mounting plate to the fully extended and "full" positions?

Nope, sorry can't help you with that. All I know is that the 60051 is a few inches longer.

The important part is the (almost) empty position. You can bend the rod to make an adjustment.

Rudi

 

[f1junky]

That's what I was thinking. Thanks

 

[shelfboy1]

the 79 tank is deeper than the 77 tank i doubt you will ever get the right reading.maybey by bending the rod and testing it you can get it close.