Hello everyone, i bought and Ford Focus c max 1.8. The year Is 2006. Now my car has no power, going up to 3000 rpm is very difficult. I bought it from a lady who has not used it for almost a year and when I start the car it gives me an engine system failure, I went to the auto electrician and as an error it gives me P0308. does anyone know how I can solve it?

P0308 is a misifre on cylinder number 8.  As there are no 8 cylinder engines in the C-Max that must be incorrect.

If it's a diesel then it's probably P0380.  Glow plug circuit.  Check the glowplugs are all still working.  Check the glowplug relay is working. 

And on the 1.8 diesel specifically, there is a bracket where the glowplug cable bolts to that melts, check whether that is still in good condition or not.  However, I'm not aware of this fault triggering limp mode on the 1.8, could it be a 1.6 instead?

Misfire detection (ish)

Change the spark plugs and HT leads and if that doesn't cure it change the coil pack

But you don't say if it's Petrol or Diesel