07 sub ltz 5.3 flex, 266,000 miles, ran fine Friday but wouldn’t start Saturday, Sunday or today(Monday), sprayed starter fluid in the intake still no start, pretty sure I have spark, check some grounds and believe that’s not the problem, initially though fuel pump at this mileage but had son crank engine and I pushed the fuel rail valve and had fuel coming out of it, changed the crank shaft position sensor and no change, could not having adequate fuel pressure make no start even if I have a 2” spray coming out of fuel rail? Will I have pressure with just the key on so I can check fuel pressure?

 

Is the check engine light on? If so, what is the code?