Read the Post, tried the solutions, still have ground problem

Rockin Lab · 11-04-09, 09:08 PM

The fuel gage wont work. Read several post on how to fix it. Touch the ground to the “hot” wire on sending unit and the fuel gage goes up. So the problem is the ground – right? I locate the ground under passenger seat. Remove ground, brush frame and wire and clean with WD40. To be sure, I run a ground straight from the battery to the ground wire under passenger seat. Gage doesn’t work. So I cut off the connector (thinking it is bad) and run a ground to an exposed ground wire under passenger seat. Gage doesn’t register. So I splice into the ground wire next to the driver seat, and run a ground direct from the battery – gage still doesn’t register. So what gives? I am turning the key on. To be sure my temporary ground was adequate, I pulled the negative cable off the battery and place my temporary ground between the cable connector and battery post. I can run the temporary ground to the positive wire on the sending unit and the gage works, so I know the ground is good. Spent way too much time on this. Any help would be appreciated.

3jvj · 11-04-09, 09:16 PM

Have you tested the sender with an ohm guage to see if it varies?

tag3 · 11-04-09, 09:58 PM

Pull sender, work up and down, clean sender, leave out of tank, turn key on, work up and down, watch gauge, take time, had to do on my 60 after getting, sat for 5 years with gas in the tank, stunk like sh!t, took way to long, works fine now.

Rockin Lab · 11-04-09, 10:08 PM

Did pull the sending unit out and cycled it a few times. Pulled hot wire off (not sure that is right term) and cleaned connection and wire.

Haven't tested the ohm. Not sure how to do that exactly, but I did buy a multi tester tool in anticipation of checking out several other wiring issues.

Rockin Lab · 11-04-09, 10:10 PM

One more thing I did:
Took a light tester. Hooked up the ground to my temporary ground, and touched the point of light tester to hot wire. It flashed off and on like a blinker.

edwjmcgrath · 11-05-09, 03:59 AM

It sounds like your sender is shot (intermittent).

Here's the resistance range for your fuel sender (from another post):
float position resistance
Full-- 17+/- 2.1 Ohms
1/2 -- 45+/- 4.5 Ohms
Empty-- 120+/-6.5 Ohms

So what you want to do is to put your multimeter on the Ohms or Resistance or Greek Letter Omega mode and at an appropriate scale like 200. Put one terminal on the positive side (after you've disconnected the wire from the gauge) and the other on the ground. Slide the sender from full to empty and check the resistance.

Most multimeters will have a symbol (mine shows "1") for infinite resistance or open circuit. You should not get infinite resistance at any point in the range on your sender. If you do, the meter will stop working at that point. These senders are not real expensive. A quick google shows an oem sender for $30 at JT Outfitters.

Luck.

Rockin Lab · 11-05-09, 07:14 AM

Thanks ed

I was afraid it would be something like that. I had everything out a week ago, and had a somewhat difficult time installing the seat frame (the tub is aluminum and the seat frame had not been installed - lots of adjustments). I messed with the sending unit while everything was out of the tub and concluded it was the ground. So put it back together, etc.
There probably isnt another way to test it with the sending unit in? I will check and see if I can unbolt just the passenger seat without removing the entire frame and attack it that way.

What happens if the ohms are off? Is that the sender needs replacement? The gage would spike for a moment after the tank was filled.

And....there are many other wiring oddities with this. For example, the water temp gage comes on immediately. One time the engine overheated and the gage went left instead of right. When the high beam is on, the right blinker signal comes on (steady - not blinking) rather than the blue light in the panel (though outside everything looks good). Turn the blinker on with high beams and the right panel lights blink - not the blinker. Everything electrical item works, but ...

Thanks again for your help

edwjmcgrath · 11-05-09, 08:25 AM

It sounds like you've got electrical demons. Not unusual in the FJ...but it's a really simple system so it should be easy to debug. Take them on one at a time.

You can start to debug your sender with a couple of simple tests. Disconnect the wire to the sender and measure the sender's resistance with your multimeter. One wire to the terminal and one to ground. Does that resistance make sense for how full your tank is? For example, if you fill the tank, the resistance should be 17 ohms. If it is infinite, then your sender is probably bad. If it is 0, then your sender is probably bad.

If you want to test out your gauge and wiring independent of the sender, that is pretty easy too. Go to radio shack and buy 3 resistors (they are cheap) Get something like 20 ohms, 50 ohms, 100 ohms. Connect the resistor to the wire that runs to the sender and the other end to ground. The gauge should read almost full for 20 ohms, about half for 50, almost empty for 100. If that works, then you can be pretty sure that your sender is bad.

Also, your original logic was probably flawed. When you connected the wire to the sender directly to ground, you made the gauge think that the sender was at zero resistance. If you look at the numbers I sent you, that means that the tank is more than full, so the meter would peg full. There's probably nothing wrong with your gauge, wiring, or ground. It smells more and more like a bad sender. Good news is that it's cheap. Bad news is that it's a PIA to install.

Rockin Lab · 11-05-09, 12:50 PM

Thanks again. This is helpful. I will take it slow and easy.

fj hunter · 11-05-09, 01:57 PM

found the gas smelly and gummy like hardened glue. pulled the tank, added 48 1/2 inch thread nuts (stainless), and added 4 quarts of 30 w oil. built a rack so i could turn the tank upside downand spin it around with 2x4s and threaded rod.

after the second day of flipping it around, and still not getting the blob out, i opened the port with the sender again and then added carborater cleaner, 1 quart.

contiuned to turn and spin the tank. 1/2" nuts started to roll after the third day.

after that the job got easy. 6 days later, 9 total, the nuts rolled and the tank came clean.

the green paint, or light blue maybe, inside the tank flaked a bit, but i did not flip/spin fast, just enought to get the nuts to slide and promote cleaning.

finshed with the second quart of carb cleaner, and then found a used sender, and put it all back together.

note to self... it, the fuel level sender, still rolls and pitches with the fuel movement, causing the fuel guage to jump around some, but at least i have an indication there is fuel in there.

oh ya, spent another 1/2 day getting all the nuts out, the last four took almost three hours. and sore arms.