Introduction
The P0304 diagnostic trouble code indicates an ignition, fuel, or mechanical failure causing a misfire specifically in Cylinder 4. The PCM monitors crankshaft acceleration drops to isolate the misfire to this specific cylinder, logging code P0304.
Common Symptoms
- Check Engine Light illuminated on the dashboard.
- Engine stumbling, shaking, or rough idle.
- Hesitation or poor acceleration response.
- Decreased fuel economy.
Primary Causes
- Faulty Spark Plug or Wire: Worn plug or damaged plug wire on Cylinder 4.
- Defective Ignition Coil: Failing coil pack supplying Cylinder 4.
- Clogged Fuel Injector: Restricted fuel delivery to Cylinder 4.
- Internal Mechanical Issue: Low compression or head gasket leak affecting Cylinder 4.
Step-by-Step Diagnosis & Fixes
- Swap Components: Cross-test the spark plug and ignition coil with Cylinder 1 to isolate the fault.
- Check Wiring Harness: Inspect the injector and coil electrical connectors for corrosion or loose pins.
- Test Fuel Injector: Verify proper injector operation and spray pattern.
- Perform Compression Check: Test cylinder pressure if spark and fuel check out.