Fiesta mk6's are prone to coilpack problems, if it feels like the car is producing half power then it will more than likley be this.

How many miles has the car got? as they can go as little as 20k, most last 60-65k. We had to change ours last month for the cost of 38quid.

if the ecu is fubbered then it will come up on the dash EAC FAIL (i think thats the code)