I'm working on a 99 flex fuel 3.0 2wd and all it does is crank over. Was driving it the other day ran good than all of a sudden spat and sputtered and shut off. Cam sensor and synchro changed, getting spark. I'm having a feeling it's the flex fuel sensor any way to check it?

 

Are the dash warning lights coming on & cycling through their self test at KOEO? If not, check the under hood PCM power relay fuse, if ok /thump/swap out the under hood power distribution box located computer power relay with a known good one not needed to run the engine, like the A/C power relay. Check distribution box contacts for corrosion or looseness of fit.
If the dash lights up, can you hear the fuel pump run for a couple of seconds & turn off, when you turn & stop the ignition key at run, Before trying to crank the engine?
If you can't hear the fuel pump run, check the in cabin fuel pump inertia cutoff switch to see if its tripped. Maybe thump to trigger it so the flag pops up, then reset it so its contact ball is making electrical connection in a new spot.
If that's ok, check the under hood fuel pump power relay fuse, if ok, wiggle/thump/or swap out its under hood power distribution box located power relay with a known good one not needed to run the engine, like the A/C power relay & listen again for the fuel pump at KOEO.
If the fuel pump runs, have you checked fuel pressure at the under hood fuel rail Schrader valve test port, it should be 64 +/-8 psi.
If fuel pressure is low, when last was the fuel filter changed?
If you have a CEL lit, scan the vehicles computers/controllers with your ELM scantool running FORScan or the like software on the viewing device of your choice & post up All pending, or set, trouble code Number clues.
The inexpensive ELM scan tool can determine if the flex fuel sensor is acting out, but it shouldn't cause the engine to not start.
Will it try to run if you spray starting fluid into the throttle body?
A bunch of trouble shooting thoughts for consideration, let us know what you find.