Cause
Blocked or restricted injector nozzle
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.
Typically specialist work. Needs equipment or training most home workshops do not have.
Codes this can cause (15)
Codes where this is a likely explanation first, rather than merely a possible one.
- P01CF Cylinder 3 Injection Timing Performance - Over Retarded Likely for this code Moderate
- P02CD Cylinder 1 Fuel Injector A Offset Learning At Max Limit Likely for this code High
- P02CF Cylinder 2 Fuel Injector A Offset Learning At Max Limit Likely for this code High
- P02D1 Cylinder 3 Fuel Injector A Offset Learning At Max Limit Likely for this code High
- P02D3 Cylinder 4 Fuel Injector A Offset Learning At Max Limit Likely for this code High
- P02D5 Cylinder 5 Fuel Injector A Offset Learning At Max Limit Likely for this code High
- P02D7 Cylinder 6 Fuel Injector A Offset Learning At Max Limit Likely for this code High
- P219A Bank 1 Air-Fuel Ratio Imbalance Likely for this code Moderate
- P219F Cylinder 4 Air-Fuel Ratio Imbalance Likely for this code Moderate
- P21A0 Cylinder 5 Air-Fuel Ratio Imbalance Likely for this code Moderate
- P21A1 Cylinder 6 Air-Fuel Ratio Imbalance Likely for this code Moderate
- P2B95 Cold Start Injection Pulse Performance Likely for this code Moderate
- P016C Closed Loop Air/Fuel Ratio Control At Limit - System Too Lean Moderate
- P050D Cold Start Rough Idle Moderate
- P219B Bank 2 Air-Fuel Ratio Imbalance Moderate
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