فوهة البخاخ مسدودة أو مقيدة

Deposits or debris narrowing the injector's spray holes, so the needle opens exactly as commanded and less fuel gets through. It is the mirror of a worn injector and the two are told apart by direction: a restricted nozzle under-delivers, a worn seat over-delivers, and the engine module's fuel trim for that cylinder runs to the opposite end of its range in each case.

The deposits are baked on by heat, which is why the middle cylinders of an inline engine reach this state first — they run hottest, with cylinders either side rather than open coolant flow. A restriction appearing there on a high-mileage engine is usually the leading edge of a set going the same way rather than one bad injector.

Cleaning is a real option here in a way it is not for a worn injector. Professional ultrasonic cleaning and flow testing can restore a nozzle narrowed by deposits. It will do nothing for a worn needle and seat, so the distinction is worth establishing before paying for either.