Stumped on Fuel Gauge

[Corts60]

Hi folks,

I used to think I was pretty decent at solving electrical gremlins, but this fuel gauge in my '86 is kicking my butt. It all started this summer when the gauge would only read 1/4 tank when it was full. This happened out of nowhere as it always worked before. It would move to E as you used fuel, i.e.: 1/8 tank would actually be 1/2 tank or so. I thought that was weird so I pulled the sender wire and put it directly to ground to test the gauge. That pegged the gauge out so I thought OK, bad sender.

I pulled the tank and replaced the sender. before I put the new sender in the tank, I hooked it up to the sender wire and ground and manually moved it and watched the gauge respond. OK, all good? Then I put the sender in the tank, installed the tank and added 6 gal of gas or so. The gauge will not come off of E. If I ground out the sender wire, It will peg full as before. I rechecked all grounds from sender to frame, frame to battery, battery to body, etc. All are 1ohm or less.

Any one have any ideas of what I am not doing correctly here?

Thanks in advance,

Cort

[JJH Jimmy]

My first guess would be that the float had a hole in it or it is hung up on something.

[Corts60]

Originally Posted by JJH Jimmy

My first guess would be that the float had a hole in it or it is hung up on something.

That’s what I was a feared of. Now I get to pull the tank again…ggrrreeeaaatttt. Haha.

[Dead Parrot]

Had something similar on my 84 CUCV. Gauge would only rise to 1/8 when full but would read E when empty. Saw a thread on the Steel Soldiers site on a similar problem that stated replacing the gauge fixed the problem. Swapped in a different gauge and that one worked normally. Only downside is it says Unleaded instead of Diesel.

It was an easy fix at the time as I had the gauge cluster out chasing issues with several of the idiot lights that were standard with the CUCV trucks. Never checked what happened if I grounded the sender wire.

The SS thread stated that one of the resistors failing in the gauge can cause that behavior.

[Corts60]

Alright fellas, I need some help here. I’ve swapped two senders, two gauges, ohm’d out the sender wire, checked all grounds. I’ve manually moved the sender by hand and watched the gauge respond. When I first start the truck for the day, the gauge reads correctly, but when the engine gets warm, the gauge goes back to E….

I’ve troubleshot a lot of wiring issues in my time, but I’m stumped. Only thing I can think of is something is heating up and causing resistance to change. What could it be?

[JJH Jimmy]

Where did you ohm the sender wire from? All the way to the gauge cluster?Possible getting resistance in the bulk head connection? I would probably start by running a temporary new wire from the sender all the way to the cluster. If that doesn’t solve it then you narrowed it down to the printed circuit on the gauge cluster.

[Corts60]

Originally Posted by JJH Jimmy

Where did you ohm the sender wire from? All the way to the gauge cluster?Possible getting resistance in the bulk head connection? I would probably start by running a temporary new wire from the sender all the way to the cluster. If that doesn’t solve it then you narrowed it down to the printed circuit on the gauge cluster.

Thanks for the reply. I ohm’d it from the connection at sender to the back of the gauge through the circuit board. This is the 2nd circuit board as well…I installed the tach upgrade kit from LMC. This problem was happening before the install and is still happening.

[ray_mcavoy]

The gauge topping out at 1/4 even when the tank is full and the sending unit & float are okay is often a sign that the resistor on the back of the gauge is bad or not making a good connection.

[Corts60]

Originally Posted by ray_mcavoy

The gauge topping out at 1/4 even when the tank is full and the sending unit & float are okay is often a sign that the resistor on the back of the gauge is bad or not making a good connection.

Ok thanks for that. At this point it has to be something I’ve already touched since I literally have touched everything. Haha. Maybe the little spring clips in the circuit board did not get seated well enough.