when i got my 90 RS a couple weeks ago the fuel gauge was reading just a little past full...guy i got it from said he had just filled it up so i didnt really think much about it....did some checking and unplugged connector behind rear seat while switch was on and gauge pegged out wayyyy past full....plug it back in and gauge moves back down to barely above full...when driving the gauge seems to float back and forth moving just a little bit either way.....when i turn the switch off the gauge will move down to 3/4 tank....turn it back on and it goes back to just above full

fuel gauge and tach are only 2 gauges that dont work(tach starts out at 4k rpms upon startup and pegs after a couple seconds) do you guys think my gauge cluster is bad or do you think its the sender?

 

anyone?

 

I dont think its either. Ive replaced the gauge and the sender in my car and it still floats around while comming to stops and stuff, ive been told its the gas in the tank sloshing back and forth

 

let me clear it up a bit

the gauge NEVER drops below FULL....EVER.....unless i shut the switch off....i ran out of gas yesterday and it was still showing just a hair above the full line....im thinking my sender is bad because i filled it up this morning and the gauge moved a little bit furthur towards being pegged out

 

All analog gauges are really ammeters. The faces are changed and calibrated for different jobs IE: Voltages, Temperature, or in your case Fuel level. The sending unit on these cars is 90 ohms = full and 0 ohms = empty. Since I=V/R, when the tank is full the meter should full, if it reads full any other time the then there must be an open circuit somewhere creating at least 90 ohm of resistance but more likely infinite resistance, causing the needle to read Full or past full all the time.
When the key is off there is no current and the gauge returns to empty. You could have a broken wire, a bad ground, but most likely a bad sending unit. The sending requires removal of the fuel tank and a new one from the Chevy dealer is over $600.00. I’ve had 2 go bad so far (2 cars).

Hope this makes sense to you. It does to me but I wrote it.

 

makes sense to me....if i have to remove the tank then im putting a fuel cell in with external pump....i found a new sending unit online for about $200 so i "might" go that route

 

Make sure it has the same ohms or it won't work with your gauge.

PS: The sending unit on these cars is integrated with the fuel pump pick-up and the tank seal and all of the fuel lines from the bottom of the tank to about 2 feet of tubing outside the tank, So if you get any sending unit other than a stock one you need to do some modifications to get it to fit and work properly.