Hyundai i800 dosnt turn over when starting up

I would get your battery LOAD tested and replaced if needed but hard to diagnose fault if not showing when checked . Also check starter / wiring / connections . Check or replace spark plugs , likewise the MAF sensor

Why would you change the spark plugs when clearly it states its a 2.5 diesel , and for someone to change the injectors as a test is expensive, Hyundai garage should know every listed fault by its description as they would get more of these through the door and 95% will have similar faults depending on the description of fault , Like a knock at drivers wheel ,Drop link would be at fault about 90% of the time with 5% being the lower wishbone and 5% the wheelbearing just as an example, engine losing power with not fault codes sounds like an ECU problem, as if the brain is at fault then it cannot point out a sensor fault , Does this make sense to you ???

Wrongly assumed it was a petrol .Why are you going on about susp, , wheel bearings , wishbones etc. that have nothing to do with the problem ?????