My fuel gauge started acting up. Sometimes it would read completely full and then it would drop to completely empty and the fuel warning light will come on. Now it just stays on empty with the fuel light on. I am not reading any codes and when I erase codes, the gauges jumps to completely full no matter how much fuel is in the tank. A short time later, it will return to empty and light. I replaced the fuel pump and sending unit, that did not correct the problem. I got another instrument cluster and again, the problem was not resolved. I performed the gauge self-check and both fuel gauges read the same in the self-check. Where do I go from here?

 

Sounds like a grounding issue.

 

I think he means 'grounding'.

If you don't have one yet, get the factory service manual for your truck from here. (you want the 98 version) Wiring diagrams are in section 8W. Check it out, see where the grounds are, make sure they are clean, and tight.

 

Damn autocorrect...

Fixed it.

 

Cool I will check that out, thank you both.

 

Check that ground between the cab and bed, on the passenger side.

And/or any grounds going directly to the tank and pump.

 

I polished the ground between the cab and bed, three grounds along the drivers side interior fender and all three grounds direct from the battery. I then went to the frame rail next to the tank and tied in a test ground from the frame to the sending unit ground. None of that had any effect. I then hooked up an after market fuel gauge and it is reading from the sending unit. I spliced into the sending unit in the bundle from the rear of the truck just before it joins the bundle passing through the firewall. Now the dash fuel gauge is displaying just under full.

 

once and a while my tach will stick but if I tap the instrument cluster the needle will pop back up. if you try this method, just don't hit the dashboard.

 

That is not the issue. Read the initial post, it is an electrical issue of some type. The replacement cluster acted in exactly the same manner. Thank you.

 

did you test the wires behind instrument cluster? might wiggle them as you test for connection