Focus Diesel Running Lean

A lean running condition on a diesel Focus like yours could be more than just injectors. Have you checked the air-fuel ratio? Is the catalytic converter working right? A bad throttle body or vacuum leak could also be the problem. What have you checked so far?

I haven't checked the air-fuel ratio directly, nor the catalytic converter. I visually checked the intake manifold for leaks, but no pressure test. How important is the air-fuel ratio here, and what's a reasonable range?

Air-fuel ratio is critical given the symptoms. I can't give a precise range without Ford's data, but any major deviation from the stoichiometric value suggests a problem. With the mileage and potential complexity, a professional diagnosis is best to avoid further damage.

Took it to a workshop, and they confirmed a defective fuel injector. Replacement and labor cost 515€. Thanks for the help.