Im using a GM fuel level sensor in my project truck wired to a 1k pull up resistor. it does function but the resolution is garbage. With my multi meter on the ADC input im getting a .008v at empty stop to .498v at full stop. would there be a circuit i could put together that would give better resolution or would i be stuck with going to different level sensor? current one is testing out at 35 ohms empty and 92 ohms full

 

You can use a lower value pull up resistor.
I would not use anything lower than 100 ohms, since you are loading up the regulated 5V source and you might burn more than 0.25W in the resistor.
Most resistors can only handle up to 0.25W.

 

You will also want to enable filtering on that input (if possible), or you're going to get lots of needle bounce from fuel sloshing.

I built a separate circuit powered off the fuel pump's 12V supply with a linear regulator and a low-pass filter, but DaWaN's suggestion of a 100 ohm resistor would work fine if you can rely on software filtering in the MS.

With a 100 ohm resistor, you would use about a fourth of the ADC bins (1.3V-2.4V range), which is likely enough. It would also keep the 5V ref current down to 50mA, which is well within the bounds of what a reasonable MS3 install will have to spare.

However, you could go much lower in resistance for the pullup and still stay within a 0.25W power dissipation bound, though it would start to tax your MS's 5V ref output.

 

AFTER TRYING DIFFERENT RESISTORS AND STILL NOT HAPPY WITH THE RESOLUTION. I THINK I MAY HAVE FOUND A BETTER WAY. IM BEING TOLD THE DODGE SENDER IN THEIR E85 CHARGERS ARE 1.1K OHMS EMPTY AND 75 OHMS FULL WHICH IS BACKWARDS FROM THE ONE I HAVE BUT ILL JUST INSTALL IT UPSIDE DOWN. THE WAY BETTER SWEEP VS THE CHEVY OR FORD VERSIONS SHOULD BE THE BEST SOLUTION. ILL KNOW FOR SURE TOMORROW WHEN THE SENDER GETS HERE AND I CAN TEST IT FOR MYSELF. ITS ONLY $75 FOR THE SENDER SO EVEN IF I MESS IT UP ITS NOT THE END OF THE WORLD.

 

No need to install it upside down. You can calibrate the MS to associate a lower voltage with a higher measured value of some parameter.

You can also improve your font resolution from one bin to two bins by not using caps lock