05 mondeo st tdci possible cam tensioner fail

Hi all was hoping someone can share some light on my situation please..

Since I bought my car about 7 months ago it's had the little rattle for a second on cold starts which I believe to be the cam tensioner but it's been fine. But last week it's been sounding rough and rattly along with being a bit under powered. I've also been having suspected injector problems also. I done a 30 mile trip few days ago and when I stopped I could hear something slapping around and was getting worse as revs were increased. i visually checked all pulleys with torch for any abnirmal movement while running but looked ok. So I got it recovered but before recovery the aa sent out a mechanic who was an idiot. I explained what problem was etc and I did not want it turned over as it's very lumpy on start up due to injectors so if it is tensioner likely to skip the timing. Anyhow he was not happy with my diagnosis and plugged the diagnostic in then decided to turn it over and engine made a strange screech and said yeah it needs a recovery :@.

So here I am in need of advice. 

I'm going to check the valve timing and chain tension are there any guides on replacements? Also any tips on removing the bottom pulley? I've been looking at battery impact wrenches but dont know how good they are? 

And anything anyone else can suggest I check before I attempt to start it providing the chain is ok

Thanks 

Lee.