My fuel gauge reads like a tacho

Last month I replaced my fuel pump assy and yesterday my fuel gauge started swinging wildly from empty to 3/4 full. I guess I could blame the instrument cluster as worn out 254,000 and tach sticks at zero occasionally at start up.Usually fuel gauge problems are loss of ground but this ground runs all the way back to the firewall from fuel pump sender.
Jef Rolison
5 iX's 88-89

Could be your SI board batteries. My instruments started "bouncing" around, or acting very ghost like. The temp gauge and gas gauge were the best dancers, while the tach and speedo just dropped dead. Replacing the SI Board batteries fixed everything as good as new.

If you aren't familiar with these batteries, toss a reply back saying so. A few of us around here have replaced them, but it isn't trivial

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1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

my temp gauge sticks in the winter, but its nothing a nice bump or a good slap on the dashboard wont fix

Quote
Earendil
Could be your SI board batteries. My instruments started "bouncing" around, or acting very ghost like. The temp gauge and gas gauge were the best dancers, while the tach and speedo just dropped dead. Replacing the SI Board batteries fixed everything as good as new.

If you aren't familiar with these batteries, toss a reply back saying so. A few of us around here have replaced them, but it isn't trivial

My SI Board hasn't accepted a reset for years- everyonce in a while I get a Service Interval Exceded Red Light caution so I dont think the batteries are the problem.
Jef Rolison
5 iX's 88-89

Hi Jef,

I think some models have 2 level senders (each side of the tank). If so, did you check both?

Also, it seems like the fuel gauge is damped, unlike the other gauges which drop instantly once you kill the ignition. Does anyone know if it is electrically (capacitor etc) or mechanically (spring etc)? If yours isn't damped, Jef, then knowing how it should be damped might give clues to what is busted.