Odd Fuel Gauge Behavior

[71FJ40]

Here is the set-up:

New Sender Unit
Dedicated Ground from "ground" of sender to chassis ground
Dedicated Ground from from instrument cluster to chassis ground

So, when turing on the ignition, the guage goes to about a 1/4 (on a full tank) and then returns to "E"

All this happens within about 10 seconds.

All grounds have been double checked and I also tried 2 different fuel gauges with the same results - ideas???

 

[Pin_Head]

Bad sender out of box?

 

[jus cruzin]

the sender unit has coils (I think copper) wound around it.......at some spots the coils may be too far appart to get correct reading .........faulty sender........you could take the sender appart to check......if they are too far appart just close the gap by moving the coils closer

the unit in my BJ40 is the origional one and every now and then the sender arm will break a coil. Remove and join again so my gague reads full = full. 3/4 = empty. half = half. empty = empty

yes I know I cheap ....like a budgie not ruff like a dog

 

[71FJ40]

OK - I now have 3 (yes THREE) OEM senders sitting here on the bench and every one of them out of the box is defective.
One measures 25ohms for 1/2 to full and open below half
The second is always open
The third varies between 20ohm and 250ohm intermittently with it being open inbetween

Anyone else with problems with OEM senders???

 

[Gord]

fuel gauge problem

I have a similar problem on my '75 fj40. First I replaced the sender since voltages at the gauge were as they were supposed to be, then replaced all wires. Resistance at sender is 24.8 ohms, which is what its supposed to be. Still shows 1/4 on full tank but drops to zero in a few minutes. On less than full tank, always reads '0'.
Have you found a solution for this yet? Thanks.

 

[65swb45]

First time I've seen this post.

71FJ40, you do know that the 71 guages share a common hot lead between oil, fuel and water, right?

And that it is the various grounds that make the guages read.

And that by grounding the guages in any other way EXCEPT from the guage DIRECTLY to the sending unit will NOT WORK.

Also, as I now understand it, the ohms readings for 72 and older are COMPLETELY different from 73 and newer. Downey has more info on this, and has posted it up in THIS FORUM before.

Best

Mark A.