🚨 Diagnostic Profile
Vehicle Make: ACURA
Technical Description: Cylinder 4 Misfire (P0304)
A Cylinder 4 Misfire code indicates that the engine control module (ECM) has detected incomplete or inconsistent combustion in the fourth cylinder. This can stem from ignition system faults, fuel delivery issues, mechanical wear, or sensor malfunctions. On Acura’s V6 and inline-4 platforms, cylinder 4 misfires are commonly linked to ignition coils, spark plugs, fuel injectors, or vacuum leaks affecting that specific cylinder bank.
🚨 Repair Difficulty Tier
Difficulty Rating: Intermediate
This repair requires the use of an OBD-II scanner capable of reading live sensor data (misfire counters, fuel trims, and ignition timing), along with a multimeter for electrical testing of coil packs and injector circuits. While replacing spark plugs or coils is straightforward, accurately diagnosing the root cause—especially if it involves fuel trim analysis or compression testing—demands intermediate mechanical knowledge and diagnostic tool proficiency. No airbag or restraint systems are involved, but incorrect diagnosis can lead to unnecessary part replacement costs.
🛠️ Resolution Steps
Step 1: Preliminary Inspection
Begin with a visual inspection of the ignition coil and spark plug wiring harness connected to Cylinder 4. Check for any cracked, burnt, or loose electrical connectors. Inspect the spark plug for cylinder 4 by removing it—look for fouling, carbon buildup, or unusual electrode wear, which may indicate a rich or lean condition. Additionally, inspect the intake manifold gasket and surrounding vacuum lines near cylinder 4 for signs of leaks, as unmetered air entering the cylinder can cause misfire codes.
Step 2: Diagnostic Verification
Connect an OBD-II scanner capable of live data streaming and monitor the Misfire Counter PID specifically for Cylinder 4 while the engine idles and under light acceleration. Compare short-term and long-term fuel trims (STFT/LTFT) for Bank 2 (if applicable) to check for a lean or rich condition. Use a multimeter to test the resistance of the Cylinder 4 ignition coil primary and secondary windings against Acura’s factory specifications (typically 0.3–1.0 ohms primary, 10,000–15,000 ohms secondary depending on model year). Additionally, perform an injector balance test or swap the Cylinder 4 injector with a known-good unit to rule out a clogged or failing fuel injector.
Step 3: Resolution & Reset Process
If the ignition coil or spark plug is found to be faulty, replace the Cylinder 4 spark plug using OEM-specified torque values and replace the ignition coil pack if resistance readings fall outside factory tolerance. If a fuel injector issue is confirmed, replace the injector and perform a fuel system relearn if required by the ECM. After completing repairs, clear the diagnostic trouble codes (DTCs) using the scan tool and perform a road test under varied load and RPM conditions to confirm the misfire counter remains at zero. Allow the ECM to complete a full drive cycle to ensure the fix is verified and no pending codes return.
📦 Parts, Labor, and Budget Estimates
Required Components/Software: Ignition coil pack (Cylinder 4), OEM spark plug, fuel injector (if applicable), OBD-II scan tool with live data capability, digital multimeter, intake gasket (if vacuum leak found).
Average Component Price: Spark plug: $8–$15 each; Ignition coil: $60–$150 (OEM Acura); Fuel injector: $80–$200 per unit; Intake manifold gasket: $20–$45.
Estimated Labor Hours: 1.0–2.5 hours for diagnostic testing and component replacement, depending on accessibility of Cylinder 4 components and whether intake removal is required for gasket replacement.