hi, i have a vn that won't start, fires once only on crank then just cranks, doesn't fire. I have checked spark, dfi and coils, replaced ecu and fuel pump, has fuel up to pressure reg and has injector pulse. Replaced CAS also. Have no idea what to do next. any help would be appreciated.

Check that your harmonic balancer is not damaged, the big rubber section often cracks and puts the TDC / cranking positions out.

Spark plugs?
Compression test on engine?