my ford fiesta ST150 recently started suffering from a loud knocking coming from the engine the engine has run 77k miles. this is more clearly heard once engine has warmed and a given a few presses of the accelerator.....i have let my car run low on oil but when checked it was on the minim mark this as caused me to take my car off the road but research is not given me any ideas to where to start to fix this problem or to how costly it would be any help would be very welcoming,

i have been told it could be a number issues starting from the following

piston slap, cracked engine block, damage pistons

If you've run it low on oil the big end bearings are knocking. You need an engine rebuild.

But where on earth do I start with it are we talking full engine rebuild or just replacing the parts that's damaged and how much am I looking at price wise?

Unfortunately, oil is cheap, engine rebuilds aren't. The engine will have to be removed and stripped so as to remove the crank for inspection.By the sounds of what you describe it sounds like big end knock. The crank shaft bearings and conrod bigend bearings have been deprived of oil and burnt, thereby wearing grooves into the crankshaft journals. The crank will have t be reground to a smaller size and new oversize bearing fitted. How much this costs I do not know now and firms capable of carrying ou this kind of work are getting scarce, Its a chuck away world.

However if you search on line I'm sure that you will find one in Cumbria, if not another option is to try to source another 150 engine. May work out cheaper.

I have a very good parts guy to go to that I trust for the sourced parts if it a a engine rebuild needed then I guess I just dive in but at least now I know where to start if I have to perchase a donor engine then so be it thanks for your help guys looks like alot of work ahead of me

get a second opinion to have a listen to the noise, it could be clattering cam chain against cam cover(cam chain tensioner failure) or could be rattly swirl flaps in intake manifold, or as others say crank bearings worn out, even if oil level on dipstick on minimum doesnt neccesarily mean crank bearing damage

is it a more deep rumble or deep rythmic knock, or clatter?

It a deep low knocking sound that's slow and steady at idle until engine has run for awhile then it gets quicker.... at first I thought it was the top end but after awhile it's seems to shift and sound more lower end....

Looking on ebay??? I'm not recommending these but to give some ideas of cost and options.

ww.ebay.co.uk/itm/FORD-FIESTA-ST-2-0-16V-150BHP-ENGINE-INSPECTION-REBUILD-SERVICE-/251809804286?hash=item3aa108affe:g:hOUAAOSweW5U3J~O

http://www.ebay.co.uk/itm/FORD-FIESTA-ST150-BARE-ENGINE-WITH-LOW-74K-MILES-ON-IT-/321776493910?fits=Car+Make%3AFord|Model%3AFiesta+V|Cars+Year%3A2008|Cars+Type%3AST150&hash=item4aeb5fa556:g:o0MAAOSwl8NVdDFn