Little confused as to your terminology when said changed regulator and checked vaporizer drain as the LP regulator and vapourizer are the same.

You should be able to find an OBD2 connector on the LH side near the battery under the hood that a common automotive code reader can hook up to.

Besides pulling codes there lots of basics you havnt mentioned like check fuses in fuse box, check inline fuse in the injector harness on the throttle body, check relays next to the battery especially relay 1 and 2, check for spark with a tester. Check vapourizer pressure (4.5psi to 6.5psi). Check for lpg leakage into intake (broken injector o ring or stuck assistant injector.) Check lpg pressure sensor and harness/connector in throttle body, Check compression, check for vacuum leaks.

Ive also seen a few harnesses rub through near the ECM connector that ended up breaking several wires.

Really you have to narrow it down more as to what your missing. Like is there no spark or no fuel.