Another thing to check is the throttle position motor. When you turn the key on the throttle plate in the throttle housing should make a slight whining noise for a second or two. If you don't hear it then it may have a bad wire in the connector or the throttle motor may have died. Broken wires in the plugs was always an issue. Did you ever locate the fine mesh fuel screen in the injector holder?? It should be under the sensor going down in the holder or there could be a metal indented cap with 2 screws on top of where it's located. S/N break. If it's plugged with tar it will not start for you either. And the injector housing could still be the culprit. There are check **** and springs that get stuck with the tar and won't feed fuel. I would double check the fuse in the red wire of the LPG fuel injector. Should be a 3 amp mini style. You have fuel to the inj holder and spark to the plugs so probably a issue with fuel not getting into the engine. Listen for that throttle motor to make it's small whining noise. That is located under the inj housing and on top of the intake manifold.