Have a 2004 Isuzu Trooper 3.0 TD in that wont start. Eng code seems to be 4JX1.

Does anyone have any info that I can have a read through explaining how the fuel system works? Im aware that Oil pressure from a separate oil pump/pickup is used to assist injector opening and the correct viscosity oil is important (Which it has). Before I go digging in too deep I'd like to have a reasonable idea of the system, what influences it and how it functions.

The last time we had one I checked fuel supply, made sure the oil pickup was intact on advise from another garage, then due to lack of understanding/com's/information sent it to Isuzu. I think it was found to be a faulty IMV. This time I'd prefer to gain some understanding of the system if possible.

Cheers.
Steve.