Gas gauge - Goes lower as I fill the tank

[Dakom]

well if you have followed my other post i got the factory gauges working well atleast the speedo but i put gas in it to test the gas gauge and it went lower i wondering if it is posibly wired backwards or if there is any thing you guys recommend checking

[4.3LXJ]

Factory gauge and sending unit?

[Mudderoy]

Factory gauge and sending unit?

I wonder why they never made and idiot light for a fuel gauge. :out:

[4.3LXJ]

Tony, mine has a low fuel light in it to remind you, just like some newer cars

[Dakom]

yes they are factory

[4.3LXJ]

That leaves a couple of possibilities. The most likely one is a bad ground for the tank. I take it by your avatar that you have been out in the mud. It can work its way under the tank straps and not allow a good ground. I suggest you reestablish the ground and it will work right again.

[olds-cool]

That leaves a couple of possibilities. The most likely one is a bad ground for the tank. I take it by your avatar that you have been out in the mud. It can work its way under the tank straps and not allow a good ground. I suggest you reestablish the ground and it will work right again.

Don't mean to threadjack but could this also cause a gauge to register lower all the time? Mine has been progressively getting worse and I do play in the mud.

[4.3LXJ]

Don't mean to threadjack but could this also cause a gauge to register lower all the time? Mine has been progressively getting worse and I do play in the mud.

That too

[Dakom]

I am begining to think its wire backwards if possible cause the more gass i use the higher the needle goes is that possible

[4.3LXJ]

I am begining to think its wire backwards if possible cause the more gass i use the higher the needle goes is that possible

Yes it is. It is not backwards wiring, but an incompatible gauge with sending unit. IIRC there was a change late in the XJ cycle from full power reading full to full power reading empty. The gauge or sending unit has been changed at some point. Most likely the sending unit due to a bad fuel pump etc.

[Dakom]

what do i need to fix this whats easier ne sending unit or new gauge or is their an easy fix idk about

[NW99XJ]

Replacing the sending unit usually involves dropping the tank. The pump, filter, and sending unit are all one assembly, and I dont think are all that serviceable. Granted you may be able to find stuff online where guys claim they rebuilt the fuel pump, and I do know there are companies selling filter socks, and things like that. But for the actual sending unit, i think you're looking at a swap.
No I'm going to stress the importance on doing as much diagnosis, and troubleshooting as you can before throwing away good money on a new unit. I would look at any interconnects, trace the wires as far as you can, look for splices where somebody may have tapped into the wiring, or spliced in a new one somewhere. Maybe the wiring harness's plug has gotten dirty,/corroded/oxidized, and the connections aren't what they used to be.
Double check ground continuity down the line (after the harness) like 4.3LXJ said, you could have a failing ground. Its more than likely the unit or the wiring, and I'm leaning towards the wiring. Its very unlikely that the gauge has anything to do with it.

[4.3LXJ]

On an 88 you can change the sending unit without dropping the tank

[NW99XJ]

On an 88 you can change the sending unit without dropping the tank

lucky!!!

[4.3LXJ]

Yeah, when the went to the plastic tank they put the sending unit on top instead of the front