My fuel gauge quit working, always shows full. and I noticed the ground strap between the cab and bed is broken, no ground. Without this ground strap attached, how is the fuel level grounded?
kerley

 

Ground strap between bed and cab is there to reduce radio interference and improve radio reception.

Fuel level sensor does not use chassis ground (fuel tank is plastic) it uses a variable resistor with a return to the gauge instead.

Always full indicates a short circuit. (if the needle droops to zero with the ignition off, if it stays up you look into a gauge cluster problem)

 

AlpineRAM, thank you for your reply.
When my ignition key is off, the fuel gauge shows empty.
When the ignition key is on, the fuel gauge shows full, regardless of the amount of fuel in the tank.
Would my situation suggest that the fuel level in-tank float is faulty?
Thank you

 

A bad float usually sinks, not float higher. Sounds like a bad sender or wire issue.....Alpine is most likely correct in diagnosing a gauge problem.

Have you had the dash apart recently?

 

Thank you, what would be a bad sender, and where would it be?

 

The sender is in the fuel tank, you will either lift the bed or drop the tank.
There is a big white ring on the tank, unscrew that, and lift out the fuel tank module (disconnect the cables and hoses first)

The float has an arm that moves a potentiometer, and sometimes the axle gets stuck, or the potentiometer gets worn out.

If you don't need the truck right now- disassemble the tank and take a look, take pictures and post them.

 

The sender is in the tank and is part of the or at least the float mechanism attaches to it. You either need to raise the bed or drop the tank to get to it by removing the 6 or 8 inch diameter locking ring then the fuel module will lift out and the sender is part way down on the outside of the module cant miss it since the float is attached to it. Personally I dropped the tank as I could do that myself without to much hassle though either get all the fuel out or run it very very low like down to E. Even 5 gallons of fuel in there sloshing around while you are trying to get it back up makes it quite a bit harder due to the additional weight but more was the sloshing around. You can stick your head up between the bed panel and the frame and see the top of the tank and wires coming out of it, follow them back as far as you can to look for chafing, break, bare wire etc not all that far if I recall before it goes out of sight or into a bigger harness and then out of sight if I remember right. Beyond that point I do not know where it goes. Do know that the plug it comes out of is a 4 wire plug but only two wires go to the tank the other two are not there/ or not missing they are not used in the diesel application.

Looks like Alpine ram posted same while I was typing

 

On your earlier reply, you ask if I had the dash out, yes, I am trying to find out why I have no working HVAC, all fuses and relay's that I have found check out as ok, that does not mean that I have not missed something. It has been raining here for two weeks, too cold to fool with it right now, so I am moving onto the fuel gauge repair, I want to understand the fuel tank system before I start. I do appreciate all advice and information sent to me. I will get back to you when the fuel tank is on the ground,
Kerley.

 

Thank you very much, I will update when the fuel tank in on the ground and opened up. I am handicapped, 72 years old and waiting for my friend to come when it stops raining.

 

The system works like this:

Switched power goes through the sender , from the sender to the gauge, and then to ground..

The less fuel there is in the tank, the higher the resistance of the sender, therefore less power to lift the gauge needle.
An "always full tank" therefore means that you have a short circuit somewhere, I'd start by disconnecting the electrical connector on the tank and then turn on the ignition.
(You can unplug it without lowering the tank)
If you still have a "full tank" your problem would be in the wiring of the truck, if you see it as empty, then you know the short is in the tank.
If the latter, reconnect the plug, take a rubber mallet and give the tank a few good whacks. Maybe this loosens the stuck float.

 

If you haven't dropped the tank yet, I recommend you lift the bed. I have dropped Chevy truck tanks before, and it (to me) is a real pain. When I had to replace the fuel-level sender on my Dodge/Cummins a few years ago, I decided I would tilt the bed. I'm glad I did - it was much less hassle. If you have a floor jack, a section of 4x4 (I can't tell you what length you'll need), and a couple of 2x4s (maybe 2' long?), you can tilt the bed. Remove the bed attachment bolts on the drivers side and loosen the bolts on the passenger side enough to let the bed rotate high enough to the passenger side yet keep the bed from sliding. Use the floor jack and 4x4 (on end) to lift the bed, and put the 2x4s between the bed and upper inner edge of the frame rail. You want the 2x4s at right-angle to the bed and centered on the inner edge of the frame rail so they cant slide as they take the weight of the bed - you'll need a helper for this. This may sound risky to some, but it worked with no problem for me with my wife helping. Of course, choose the method you feel most comfortable with - the risk is yours.

I applaud you for still twisting wrenches at your age - I'll probably still have to be doing that myself when I hit your age (I'm mid 50s now - how did that happen).

 

Texasprd, Thank you for your reply, your method is what I will do. I live on my small farm and will use my Tractors front end loader for the lifting, then block the bed off the frame with 2"x lumber, one of my friends will help me Saturday if It's not raining. Once I have good access I can check everything out. kerley.

 

If you tilt the bed and use 2x4s to stabilize it- cut a "swallows tail", a V-shaped cut into the end that you put on the frame rail. It can't slip out like that.

Take care!

 

Alpineram, Thank you, one more question, maybe someone has the accurate answer....What should the amperage or voltage be at the fuel gauge sending unit,
kerley

 

I found it a lot easier to drop the tank, 2 bolts and the sender attachments. I lowered it on a floor jack with a 3' 2x12 to stabilize....just my .02