Chevy Cruze Cylinder 4 Misfire: What to Check First
A cylinder 4 misfire can come from ignition, fuel, compression, or an air leak. Work through the causes in a testable order instead of replacing parts at random.
Confirm the code
P0304 identifies a cylinder 4 misfire. Note any other codes—especially lean, boost, or airflow codes—because they can point to a shared cause.
Ignition check
Inspect the spark plug and coil/coil-pack connection. Compare the plug with the other cylinders for oil, fuel fouling, damage, or an abnormal gap.
Air and PCV leaks
If the misfire started after valve-cover or intake work, inspect every hose, seal, connector, and PCV connection that was touched. A vacuum leak can create both lean codes and misfires.
If ignition and air check out
Move to injector operation and a compression/leak-down test. Mechanical problems should be ruled out before expensive parts are ordered.
Bottom line
Diagnose the cause before ordering parts. Vehicle configurations vary, so verify specifications and procedures for your exact year, engine, and model.