Hi,
I will check the vacuum on one of the other cars to confirm the gauge is accurate (it's a cheap boost gauge from my Mondeo which also reads vacuum). I've ordered a new high quality vacuum gauge so I'll check again with that when it arrives to confirm the reading is correct.
Yep I'm pretty sure vacuum leaks can be ruled out - I've spent weeks looking for one with no luck, pretty much everything in that area has been checked or replaced (except brake booster).
With the timing figures, I did read that these are supposed to be around 0. From what I've read, up to 5kw +/- is "within tolerance" but this was for the 2.7T engine.
From what I can see, the small timing chains are adjusted by oil pressure. See page 22 of the following link:
http://www.kpematop.com/S6/V8-5VEngine.pdf
I know it's a common problem on these engines for the "chain tensioner slide pads" to break and cause the chains to rub. It does rattle for a couple of seconds on startup but this appears to be normal (or very common at least!).
Not my video but it sounds similar to this on a cold start - maybe not quite as bad as this though:
https://www.youtube.com/watch?v=sUUw7ze5-3o
Could this affect the timing?
The timing idea does sound a good one as I think the belt was done at a small non-specialist garage. They're supposed to be quite hard to fit properly without the correct locking tool.
The only thing that gives me doubt is that the MPG seems to have got gradually worse over the last few months.
Is the info I posted earlier about the MAF sensor of any interest? (short-term fuel trims still high with MAF disconnected)
Thanks for your time