Big Engine issues urgent help needed please

Hi everyone

Got a series 3 bodge job in with me at the min, and it wont fire up 300tdi engine fitted.

Put a fully charged battery conected direct to starter, earthed back to battery and live to selonoid,(2 brand new starter motors tried and 1 second hand off spare disco) It turns really slow then almost stops then turns again almost as if its trying to force itself through a turn.

Will tow start but once running kicks out masses of smoke and sounds awfull.

Tried it with no aux belt and still the same!

electrical or mechanical????

This really has all our mechanics stumped!

Does anyone have any ideas, our best idea is a petrol match combo fix

Maybe bent conrod or valve causing the black smoke and friction so starter won't turn it

timing out, cambelt shredded and jamming up

Cheers for the replies chaps, turns out its a glowplug issue permenantly live, if you take the glowplug loom off works fine, put it on draws all power, so isolated the glowplugs to a separate manual circuit and all so far apperes well