checked recomended battery
610 cca (cebtury battery)
What about the starter motor? just a suggestion, caused a few issues for me, slow cranking when cold being one of them, until it got worse and started affecting more than cold starts.
Could be a long shot, but have you had the engine compression tested hot and cold?
I used to work with a guy who's LPG/Petrol GQ patrol did the same as yours. He did a comp. test hot and cold and got different results. Turned out the head was warped. When the engine was warm, it started no problem. Probably because the head expanded enough to give it a better compression. First thing in the morning, it turned over normally, but wouldn't start.
As I said Its a long shot.
Is it the V6 motor? What is the timing like?
Camper man, couple of things we have had in the shop. Oil viscosity too high for outside temp, causes the lifters to over pump and hold valves slightly open. ( this causes semi firing of the engine but no start until engine oil temp rises and viscosity is reduced) cold sticky oil pressure relief valve causes same problem.
Check temp sensor unit, if this circuit is earthed the ECU will presume a warm engine and not go into cold start mode. Its easiest to check the injection pulse when cranking, should be longer on cold start and cranking.
Perhaps the issue is too much fuel altogether?
With *non injected* cars when they get flooded the easy way to start them is to jam the accelerator pedal to the floor before turning the key - Dunno if you can do this with a injected car though to try see if it starts straight up from cold doing it the same way? (which might confirm too much fuel?)
Just thought i would chuck the suggestion in as you mentioned stupid suggestions were ok at this point and perhaps it is