matteomayer10
Focus Diesel Running Lean
Summary of the thread
A 2018 Ford Focus diesel is experiencing a lean running condition, characterized by reduced power, a check engine light, rough running, and jerking during acceleration. The initial suspicion is a faulty injection system, possibly involving a bad valve or injector. Further suggestions include checking the air-fuel ratio, catalytic converter, throttle body, and potential vacuum leaks. Ultimately, a professional diagnosis confirms a defective fuel injector, which is replaced to resolve the issue.
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4 comment(s)
matteomayer10 (community.author)
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?
marchimmel6
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.
matteomayer10 (community.author)
Took it to a workshop, and they confirmed a defective fuel injector. Replacement and labor cost 515€. Thanks for the help.
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FORD
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FOCUS
marchimmel6
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?