@nightrunner84 can you run your spare under that tank?
Are you using the GM oil pressure sensor for the fuel pressure
@nightrunner84 can you run your spare under that tank?
The readings bouncing all over the place is from the lack of averaging, lack of a low pass filter into your ADC or could be exactly what your fuel pressure is doing. On my truck the fuel pressure waves around about 1 PSI and a non-dampened mechanical gauge shows the same thing.
For the lowpass filter try this circuit below. This also protects your ADC input incase the sensor wire shorts to battery voltage.
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I get most of my parts from digikey and for prototyping most of it comes from old electronics. You should be able to find them on amazon and eBay also.