Can someone tell me how the cylinder deactivation works on the new Focus,I know if you put it into eco mode it shuts down the middle cylinder of the three,therefore saving fuel,but if you need to speed up a bit or hit an incline does it then labour as it’s only using 2 cylinders or does it re engage   the third cylinder automatically so that you don’t have to keep changing between eco and normal mode manually? 
 

The deactivation works on partial load and light throttle. It will disengage when outside these conditions . It can change cylinders in 14 milliseconds. 

I have been doing some live monitoring with FORScan just to satisfy my curiosity and it is surprising just how often Cylinder Deactivation is activated, even at 70 MPH in 6th gear on a manual car and sometimes even when going up a long incline on a light throttle.

As @iantt indicated as soon as you squeeze the throttle even slightly it switches back to 3 cylinders but activates again if you ease back on the throttle.

It may work differently on a Automatic car and I never use Eco Mode so I don't know if it behaves differently in that mode, but it does work in Sport Mode.

I have never tried it with Cruise Control on either, but I would guess that it would not activate very often unless you were on a very flat road.