When your 2021 Ford Mustang displays the P0305 code, the powertrain control module has detected repeated misfires in cylinder 5. The 2021 Mustang is available with either the 2.3L EcoBoost four-cylinder or the 5.0L Coyote V8. P0305 is only valid on the V8-equipped Mustang GT models, as the four-cylinder EcoBoost only has cylinders 1-4.
Confirming Your Mustang's Engine
The 2021 Mustang EcoBoost features a 2.3L turbocharged four-cylinder producing 310 horsepower. The Mustang GT has the 5.0L Coyote V8 producing 460 horsepower (480 in Mach 1). If you have an EcoBoost, P0305 is anomalous. If you have the GT, proceed with V8 misfire diagnosis.
Cylinder 5 Location on the Coyote V8
Ford's 5.0L Coyote V8 uses a traditional firing order of 1-3-7-2-6-5-4-8. Cylinder 5 is located on the driver side bank toward the rear of the engine. The Coyote engine's high-revving nature and variable valve timing system require precise ignition and fuel delivery.
Common Causes on the Mustang GT
Spark plug issues are common, especially if the Mustang is driven enthusiastically. The Coyote engine uses unique spark plugs that must be properly specified. Ignition coil failure can occur individually. The variable camshaft timing (Ti-VCT) system depends on proper oil quality and can affect cylinder performance. High-performance driving increases stress on all ignition components.
Diagnostic Process
Verify your engine type first. On the GT, access cylinder 5's spark plug on the driver side rear. Inspect the plug for wear, fouling, or electrode damage. Test the ignition coil. Check for vacuum leaks around the intake manifold. Monitor oil level and condition, as the Ti-VCT system requires adequate lubrication.