Powertrain, generic (extended)

P23F9 Cylinder 8 Injector B Air-Fuel Ratio Imbalance

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

P23F9 points to cylinder 8, the highest number on any V8. GM's 2019 tables for the LT5 Corvette show how far a V8 with port and direct injection resolves imbalance in practice: only bank by bank. For bank 2 the monitor samples the front oxygen sensor once per cylinder event, normalises the variance against a map and fails when the filtered ratio exceeds 0.75, a Type A fault that turns on the MIL after one trip. A cylinder code that also names the injector therefore needs more than the bank-level method can deliver, and no manufacturer has published that it uses P23F9. Ford's Coyote 5.0 since 2018 and Toyota's 2UR-GSE are further V8s with dual injectors. Which bank cylinder 8 sits on follows the maker's numbering; P21A3, P0308 and P21D6 help.

Likely causes

Injector B of cylinder 8 with wrong flow rate

Leak at the intake runner or PCV connection near cylinder 8

Front oxygen sensor of the bank giving a distorted signal

Symptoms

Check engine light on
Bank-level imbalance code (P219A/P219B) stored as well
Normal drivability in most cases

Repair estimate

DifficultyHardWorkshop job

Parts and labour€120–1,000

Time1–6 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

fuel injector b cyl 8

References: gsi.ext.gm.com, law.cornell.edu, en.wikipedia.org, en.wikipedia.org.