Powertrain, generic (extended)

P23F8 Cylinder 7 Injector B Air-Fuel Ratio Imbalance

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

P23F8 identifies cylinder 7 and its injector B, so it needs at least seven cylinders, in practice a V8 or V10. Three V8 families using a pair of injectors in every cylinder are on record: Ford's 5.0 Coyote, which gained direct injection on top of port injection for the 2018 Mustang GT and F-150; Toyota's 2UR-GSE with D-4S in Lexus F models and the LC 500; and the supercharged GM LT5 in the 2019 Corvette ZR1, whose port injectors are driven by a separate fuel injection control module and listed as injector B (circuit codes from P21CF, Type A). None of them publishes P23F8; GM and Ford judge imbalance per bank. To narrow cylinder 7 down, use P21A2, the misfire code P0307 and the circuit code P21D5.

Likely causes

Port injector of cylinder 7 clogged or leaking

Intake leak at cylinder 7

Fault in the separate injector B driver module, where fitted (e.g. GM LT5)

Symptoms

Check engine light on
Fuel trim of one bank off while the other bank is normal
Rarely a perceptible misfire

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 7

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