Jumping gas gauge needle

[StellaLunaGardens]

The day I brought my RV home from the mechanic, I put $40 gas in the tank, on the way home the needle was jumping back and forth between 1/2 and empty.  Today I changed the fuel filter, started her up and the needle is on empty and never went up, (I did not drive it anywhere today, so I don't know if it would have jumped like before.


The tank has a locked cap, and it doesn't look like it was messed with.


What would cause the jumping & being on empty today?

[Froggy1936]

The jumping most likely Was a bad connection (probably inside of the tank) Adding fuel opened the connection !   Test is to ground the wire to the gauge , At the tank This should show a full reading ! If there is a pump in the tank be care  full of grounding wires , Grounding pump feed is a No No ! Frank

[Rickf1985]

The most likely problem is a bad sender in the tank but it can be several things. Always check the easy things first. You need to check the ground wire on the tank and where it attaches to the frame. Also need to check the sender wire where it attaches to the tank. How are all the rest of the gauges on the dash? Do they all work correctly? If not it could be a bad dashboard voltage regulator.

[StellaLunaGardens]

The most likely problem is a bad sender in the tank but it can be several things. Always check the easy things first. You need to check the ground wire on the tank and where it attaches to the frame. Also need to check the sender wire where it attaches to the tank. How are all the rest of the gauges on the dash? Do they all work correctly? If not it could be a bad dashboard voltage regulator.

The other gauges are working fine.


Thank you for the advice.

[StellaLunaGardens]

The jumping most likely Was a bad connection (probably inside of the tank) Adding fuel opened the connection !   Test is to ground the wire to the gauge , At the tank This should show a full reading ! If there is a pump in the tank be care  full of grounding wires , Grounding pump feed is a No No ! Frank

What do you mean by ground the wire to the gauge?  How do I know if there is a pump in the tank? And how do I avoid grounding that?

[LJ-TJ]

Odds are pretty good you don't have to worry about a pump in the tank. I don't believe the 60's 70's rigs had pumps in the tank. Take some sandpaper and clean off a spot on the gas tank and then take some sandpaper and clean off a spot on the frame. Take a piece of wire and hook it between the two spots and see if that fixes your problem. That should give you a good ground. An alligator clip will do the same thing. If that doesn't fix your problem and since your gauge works half assed then my guess would be the sending unit in your gas tank. Which would mean replacing your sending unite in your gas tank. Hm?

[StellaLunaGardens]

Odds are pretty good you don't have to worry about a pump in the tank. I don't believe the 60's 70's rigs had pumps in the tank. Take some sandpaper and clean off a spot on the gas tank and then take some sandpaper and clean off a spot on the frame. Take a piece of wire and hook it between the two spots and see if that fixes your problem. That should give you a good ground. An alligator clip will do the same thing. If that doesn't fix your problem and since your gauge works half assed then my guess would be the sending unit in your gas tank. Which would mean replacing your sending unite in your gas tank. Hm?

Thank you!

[BamBam]

Here's what your looking for at the tank, note the pic. https://www.forbbodiesonly.com/moparforum/threads/fuel-tank-sending-unit-fuel-gauge-ground-strap.70659/
Make sure the lines are clean and good metal, also check to see who worn the strap is. I have taken wire and 2 hose clamps and used then to help with ground for the gauge.
If you have a service manual, that will show & tell you more. BTW, any Mopar site that deals with cars will have the same motor, drive train, and pretty much any tech info you may need, like the one I posted. I'm a diehard bleed Mopar guy! Good Luck