Fuel Guage Goes Up Then Partly Fades -- 72 Swinger
Hi all. Apologies for the long story.
I'm on a quest to have a working fuel gauge in my 72 Swinger-- I've read virtually every post on this site and I clearly still have a lot more more troubleshooting to do. But as I go through everything, I'm having a problem that makes little sense to me.
When I turn the key, the gauge moves up to a fair representation of where the fuel level is. But then over the next few seconds, it fades back to roughly half of what is a fair representation. See the video below -- all I did was turn the key.
The facts:
Previously nothing was working, but I am getting action now that I replaced the IVR with what Classic Industries claims is a solid state unit.
The tank has a new(ish) spectra FG69B sender. I know these aren't terribly accurate, but I haven't seen anybody suggest that it could register changing resistance when the float is at a fixed level. I have a NOS sender that I plan to put in when I'm ready to get down on the floor, but I was hoping to get everything in working order before I do so.
I have a ground strap from the sender to the metal fuel line. The wire from the sender to the dash checks out fine. All the connections are clean. And the gauge goes to full and stays there when I ground the sender connection (no fading).
Just trying to see if this is familiar to anyone, and (given my limited time to work on this) see if my next steps in troubleshooting seem like the right direction:
1) Check to see if its just a really bad Spectra sending unit. Test everything as-is with the NOS mopar sender (out of the tank) hooked directly to the fuel gauge pin and a ground. Move it through its motions and see what I get on the gauge. If it works, I know I only need to swap the senders. If it still fades, go to #2.
2) Measure the voltage output of the new IVR. If it wanders, then I know it's a dud. If it's a steady ~5 VDC, then move onto #3.
3) Check the quality of the ground on the fuel line that the ground strap goes onto. It seems like a longshot that it's a bad ground with resistance that stays in the 10-80 ohm range (evidenced by the gauge needle staying in bounds) but maybe something weird here? If the ground is good, then #4.
4) Could the gauge itself be toast? Has anyone seen them fail in this way? Do I have to buy a few resistors (like a 10, a 40, and an 80) and use a 5 VDC source to bench test it or is there a better way?
It's not that complicated of a system FFS! But it's also not just sitting on the bench and easily tested. Each test requires dropping the steering wheel, pulling the cluster, crawling under the tank, and all that. So I'm looking for some wisdom or knowledge of this problem just to see if I can narrow it down.
