Can’t figure out my fuel guage

[OldMan89]

My truck has a brand new in tank sending unit but my fuel guage doesn’t really work…some times I’ll start it up and BOOM it jumps right up but after about 3 minutes it has slowly made its way back down to empty. Not times it just downst move. I’ve checked connections and fuses but I am coming up stumped. Any input on what to look for would be greatly appreciated!

 

[ThatOneGuy]

Have you checked the wire harness at the plug for the cluster, or check for damage/corrosion in the cluster it's self.

 

[RonD]

There is an anti-slosh module on the back of the instrument cluster, and you can test the sender OHMs when cluster is out

1989 sender should have these OHMs
16 ohms empty
160 ohms full

Sender wire at cluster will be the only yellow wire with white stripe on a connector

Hook up OHM meter to yellow wire and Cab ground
Should read between 16 and 160 ohms
Rock the truck, so gas sloshes around in the tank and ohms should change as float goes up and down
If you see that then sender and wire to dash are OK

Anti-slosh module is there to prevent just what you saw, OHMs going up and down every time you go around a corner, lol
It between the Yellow wire and the gauge, it averages the ohms over time, so no abrupt changes in the needle
Your symptom of the needle changing after a few minutes does read like a failing module


Google: 1989 Ford Ranger anti-slosh module

There will be videos and how-tos to repair, replace or bypass this unit

Get some dash bulbs, good to replace all 6 while dash is out, they are not expensive

 

[OldMan89]

There is an anti-slosh module on the back of the instrument cluster, and you can test the sender OHMs when cluster is out

1989 sender should have these OHMs
16 ohms empty
160 ohms full

Sender wire at cluster will be the only yellow wire with white stripe on a connector

Hook up OHM meter to yellow wire and Cab ground
Should read between 16 and 160 ohms
Rock the truck, so gas sloshes around in the tank and ohms should change as float goes up and down
If you see that then sender and wire to dash are OK

Anti-slosh module is there to prevent just what you saw, OHMs going up and down every time you go around a corner, lol
It between the Yellow wire and the gauge, it averages the ohms over time, so no abrupt changes in the needle
Your symptom of the needle changing after a few minutes does read like a failing module


Google: 1989 Ford Ranger anti-slosh module

There will be videos and how-tos to repair, replace or bypass this unit

Get some dash bulbs, good to replace all 6 while dash is out, they are not expensive

Thank you so much! I appreciate you!