Did you get any luck with the problem you had?
I hope you did.

I am having quite the same problem same make and same Nissan engine lpg. The only thing in mine is that if i pulse manually the assist injector during cracking, it will start and if kept at half throttle for a minute , it will then run without any problems, and the assist injector works fine when the full throttle is applied, but not during cranking.
I am not sure if it needs to work during starting or will the ecm use the main injector to start.

Quite **** off now, i am an electrical technician and i repair other stuff for this client but this lifter was an extra, which will not accept another time.

Any help appreciated.

Regards
Cpur