The engine will not start but will crank?

I have gotten down to my fuel pump. I’ve replaced it and it still will not come on. I put power straight to it, and it came on, so I know it works. I’ve checked the fuse and the relay, both are good. I tested the ground at the pump, and it is good. I tested voltage at pump as well. Almost 12 volts when key turns on, but quickly drops to 6 volts. I only get about 9 volts when cranking. I’ve checked the roll over switch and replaced the crankshaft position sensor as someone else suggested.