I’m hoping someone can give me some help, I have a 2003
Focus 1.6.

I’ve had this car about 10 months, I was given it by a
family member and I wanted to bring it back up to a nice condition so I would
have a decent car for the next 2-3 years as I’m saving for my first house!

Basically it has an intermittent engine rattle which sounds
to me like pinking, this happens just as you apply light throttle for around
2-4 seconds. I have spent so much time and money trying to rectify this but I have
now run out of ideas and things to replace.

So far I have changed:

Engine (the old one was using a lot of oil so I replaced it with a low mileage unit)

CAT (had the original fitted so thought I would replace this)

Up-stream (pre-cat) lambda sensor

Spark plugs, leads and Coil pack (all genuine Ford)

MAP sensor

CHT sensor

Knock sensor

Fuel vaporizer

ECU

Fuel Filter

Fuel pressure regulator

PCV valve and breather pipes

I have tried running the car on higher octane fuel and it made no difference.

I have checked all pipes for damage or collapsing.

It only ever does this when warm and the hotter the weather the worse it is (it hardly does
it at all in the rain)

The only things I am now left with is low fuel pressure although this doesn’t explain
why it only does it when hot and the downstream (post-cat) lambda but I didn’t think
this affected fuelling, I thought it was purely there to monitor the cats efficiency?

Please help!

Since you've changed just about everything except the gear box an the chances of getting a replacement part with exactly the same problem is rather unlikely, might it be something completely different to your current train of thought, perhaps structural, Heat shields, panels etc, perhaps when warmed its expanding, causing it to rub or vibrate.

I think my idea of a "rattle" and "pinking" is somewhat different to yours, I sometimes get a "rattle" under light load and I'm almost certain its the gearbox and or clutch, a few folk have said this is normal tho...