Help please

Hi, I have a 6NZ C15 that will not start after sitting overnight but only if parked on an angle lhs down, it winds over trying to fire for about 5-10sec as if sucking air then fires up and runs fine all day. It starts fine if parked on level ground. I have replaced fuel return check valves,primer pump and injector return line from rear of head. The fuel transfer pump was replaced about 200,000km ago and is not leaking fuel from tell tale. I have checked tank pick up tube and lines all look ok. This is doing my head in I cant work it out. Any help would be greatly appreciated.

 

Replaced both mate still no luck

 

Replaced both mate still no luck???

 

Also replaced hose from filter head to injector pipe and hose to supply pump the other day it is definately loosing prime somewhere as I primed this morning only about 1 and half pumps till hard and fired up ok. Cant find any leaks gonna pressurize tank when I get home saturday and spray some detergent around and see what I can see.

 

Yea mate it's all a bit of a mystery

 

Nice lookin truck by the way.