Diagnosing fuel gauge / level senders

[Semblance]

I'm trying to figure out exactly what is making my fuel gauge read incorrectly. It stopped working right a few years ago, it tends to show less fuel than actually is in the tank. It generally doesn't bounce around, though sometimes after reading empty for a while, it corrects itself and bounces back to about half or quarter tank.

I cleaned and tightened the nut on the back of the gauge when I swapped clusters last summer, no better. Everything else works on the cluster. I kept the same gauge from my original cluster as the new one was cosmetically challenged.

I checked resistance of the level senders on a full tank. I get 0.7 ohms at the pump sender (pass side) and 4.5 ohms at the drivers side sender. So I'm sensing a problem with the drivers side level sender at least, since it isn't reading 0 when full.

BUT I thought I would also jump the connectors and watch the gauge. So I disconnect both senders. When I jump the drivers connector (where I think it's connected to a bad sender) the gauge reads 5/8 full. When I jump the passenger side... Nothing. Sure enough, plug in the connector and it does nothing. Checking voltage, I get about 7v at driver and 0.22v at passenger. Ground is good at passenger. So I think that means it's shorting out somewhere between the passenger sender and the gauge. But it's weird as the gauge WILL read empty - and I would think this would lead to a false FULL reading. The gauge is rarely showing more than 7/8 full.

I'm trying to sort out next steps. Any advice on the next thing to check? Should I go ahead and replace the drivers sender? Is there a way to check what resistances the cluster is seeing at the cluster itself, so I can determine if it's a cluster problem or a wiring problem?

Thanks....!

[uturn]

Had a similar issue, for me, the solder on the cluster board was worn away so it didn't contact the gage. Tightening the nut didn't help. I had to flow solder to bump up the contact point.

[Semblance]

oh that's irritating. i really hate working on the cluster, which is why i was trying to see if the problem was elsewhere.

and i just figured it out. the senders are wired in series, and the wire that connects between them is grounding out between them at the drivers side... which is why jumping that connector worked - it shouldn't have worked without the passenger connector also installed. i guess it's open as well as grounded since there's no continuity between the senders. i wired the senders up with test leads instead of the connectors and the gauge is working perfectly.

so... can i fix this without dropping the tank? there's no slack on the wires, and i tried fishing a coat hanger from one sender towards the other under the body panel, but there seems to be an obstruction. i really don't want to run a wire through the covers and under the seat.

any other way to route a wire under there? i don't know my way around the tank.

thanks....

[dnguyen1963]

Take your sender out of the tank. Spray in carb cleaner (there should be some small holes) and shake the floater up and down vigorously. Repeat until the carb cleaner is clear. That should help with the reading accuracy.

[Semblance]

thanks - i think i'm going to replace the sender in the end. but right now the passenger side sender is basically not connected due to the wiring short, that's the bigger issue - even if i get the drivers sender working, i still won't have a valid reading.

[fight4life28]

Mine does the same thing, gets alittle bouncy depending on how much gas I have in the tank.