fuel gauge problem

[69camarokid]

wasnt really sure where to post this so fell free to move it if necessary.

I have an aftermarket sunpro fuel gauge in my 69 camaro.
For some reason the needle, when the tank is full, will sit at 3/4 full.
And as the tank empties the needle will move towards the F (full mark). When the needle is at the F, the tank is empty. Its really weird.... and annoying. And causes me to run out of gas all the time.

Ive changed out the fuel sender and nearly every part on my fuel system is brand new. But i had this problem befre ai put all those new parts on it. When i got the car with its original gauges it read the gas incorrectly, not in the fassion it does now, but still it was way off. Any ideas on how to fix this would be great, thanks.

[Bryce]

Is the resistance of you the sender matched to the gauge calibration.

I think GM is 0-90ohms. It sounds like the gauge may be reading 30-0.

[69camarokid]

Is the resistance of you the sender matched to the gauge calibration.

I think GM is 0-90ohms. It sounds like the gauge may be reading 30-0.

i dont know at all. I just bought the gauge and replugged in the original wires where it told me too

[ErikLS2]

Falcon is correct, the GM sender is 0-90 ohms. Did you make sure the gauge you bought was for this type of sender? They're not all the same, Ford has a totally different resistance range for example. The gauge you have should say somewhere on it 0-90 or whatever range sensor it's meant to work with

[69camarokid]

so when i find out what ohm resistor i nedd i just sodder it into the line?

[Vegas69]

I'd verify your sender is good. You can measure the resistance at the tank when it's close to empty. You should see very low ohms. Say 10-25. Regardless of the gauge you shouldn't see the gauge go towards full as your tank emptys.

[ErikLS2]

Todd is right and great pictures. I think you have a Ford gauge though. Ford senders read higher resitance when empty and lower resistance when full, GM is just the opposite 0 ohms at full and 90 ohms empty.

So, if you have a fuel level gauge for a Ford used on a GM then as the resistance of the fuel sender decreases as you use fuel, the gauge meant for a Ford will go towards full. If you can't find out if the gauge you bought is for a Ford, remove the wire that comes from the gauge at the fuel sender and ground it (through a 10 ohm resistor if you have one), if the gauge pegs at full, it's the wrong gauge.

[6'9"Witha69]

x3 on the Ford gauge.

[Vegas69]

Todd is right and great pictures. I think you have a Ford gauge though. Ford senders read higher resitance when empty and lower resistance when full, GM is just the opposite 0 ohms at full and 90 ohms empty.

So, if you have a fuel level gauge for a Ford used on a GM then as the resistance of the fuel sender decreases as you use fuel, the gauge meant for a Ford will go towards full. If you can't find out if the gauge you bought is for a Ford, remove the wire that comes from the gauge at the fuel sender and ground it (through a 10 ohm resistor if you have one), if the gauge pegs at full, it's the wrong gauge.

Great call