99 4Runner Gas Gauge Issue. Where to start.

[Temple90]

I noticed on Monday that when I turn the 4Runner on it shows gas gauge as full and second later it drops to empty and gas light starts flashing.
I have done my research and am seeing everything from burned out board to fuel sending unit.
Anyone have any ideas of where to start looking?
**Not sure if this is in anyway related as I do not see how it can be, but the gas gauge stopped working as soon as I got it back from the shop that was welding my exhaust. I am guessing it is just an unfortunate coincidence.

 

[dogtail]

My fluctuating 99 fuel gauge was due to bad cluster board doing what yours is, so it was an easy quick swap out. Only thing is it carries the digital odometer reading. But wasn't a big deal for me. Gauge swap is easiest thing to due if you have access to another cluster, then you get into tank.

 

[gamefreakgc]

Similar thread popped up today with same issue: 3rd gen gas gauge issue

 

[Stucco17]

Reviving a very old thread but I just fixed this problem today after many days of troubleshooting. I had the exact same issue as you (Gas gauge dial shoots to full upon turning key to "ON" then falls below empty). The problem appears to have been a burned out terminal on the cluster. It was next to L9. Cleaned it with alcohol, resoldered it, and gauge finally works. I also cleaned the fuel gauge receiver terminals and cleaned the dust off the boards. I would post pics but apparently I still can not..heres some visuals of what i mean hope it helps!

3rd gen fuel gauge problem: I think I figured out the problem (pics) - Page 3 - YotaTech Forums

 

[Grgg1978]

Check the fuel sending unit ground for continuity. Mine shorted and it would work sometimes and others won't or it would show the wrong level of gas. Easy to check once you figure out which wire it is, its right under the rear passenger seat. Just splice a new ground and you should be good unless its one of these other problems.