Is it the 1.6 fiesta zetec s or 1.4? I know these had issues with the bottom ends failing from low miles if not serviced well. Normally accompanied with loss of oil and smoke.

May be worth getting it looked at to see if it the bottom end letting go.

The upside is you can get another lump pretty cheaply and throw it in. Just make sure you see the replacement lump running and dont just trust the seller or rely on 30 day warranties, not much good if you have to rip it back out and send it back etc.