P0304 Code: Ford F-150 (2021-2024) - Causes, Symptoms & Fixes

CODE MEANING AND SEVERITY

• Code: P0304 stands for a misfire detected in Cylinder 4. The Powertrain Control Module (PCM) has detected that Cylinder 4 did not fire as expected.
• What it means for the 2021-2024 Ford F-150: A misfire can be intermittent or sustained. The engine may run roughly, shake, or lose power. If the misfire persists, it can cause increased exhaust emissions, reduced fuel economy, and potential damage to the catalytic converter. In some driving situations, the vehicle may enter a limp or reduced power mode to protect the engine.
• Recalls status: No recalls found in NHTSA database for this make/model/year/issue combination.

COMMON CAUSES ON FORD F-150

• Faulty spark plug in Cylinder 4 (worn or fouled).
• Faulty ignition coil/cylinder 4 coil (weak spark or no spark).
• Faulty fuel injector for Cylinder 4 (restricted spray or failure to deliver fuel).
• Wiring or connector issue to the Coil-on-Plug (COP) assembly or injector (damage, corrosion, bad grounds).
• Vacuum/air intake leak near Cylinder 4 affecting the air-fuel mix.
• Low compression in Cylinder 4 due to valve, piston, or ring issues (less common but possible in high-mileage engines).
• Dirty or incorrect fuel/air sensor readings affecting Cylinder 4 fueling (MAF/MAP, and related sensors can contribute to misfire symptoms).
• PCM/ECU fault (rare; typically diagnosed only after ruling out common mechanical/electrical causes).

SYMPTOMS

• Rough idle or engine vibration when stopped or at low speed.
• Noticeable loss of power or hesitation during acceleration.
• Engine runs lean/rich roughness, sometimes with a stumble.
• Check Engine Light (CEL) or MIL illuminated with P0304 stored or pending.
• Potentially increased fuel consumption.
• Inconsistent misfire pattern if the issue is intermittent (may see P0304 with occasional misfire while other fuel trims are normal or near limit).

DIAGNOSTIC STEPS

Begin with a systematic, methodical approach. For 2021-2024 F-150 engines, some access to cylinders and components varies by engine family (2.7L EcoBoost, 3.5L EcoBoost, 5.0 V8). Adapt steps to your exact engine layout.

Verify and document

• Use an OBD-II scanner to confirm P0304 and note freeze-frame data (RPM, load %, throttle position, engine temp).
• Check for related codes (P0300 for random/multiple misfires, or P0301-P0308 for other cylinders). Note any fuel trim abnormalities (short and long term).

Visual and baseline checks

• Inspect Cylinder 4 spark plug for wear, fouling, oil fouling, or improper gap. Replace if worn or fouled.
• Inspect coil-on-plug boot and electrical connector for Cylinder 4. look for oil contamination, carbon tracking, corrosion, or loose connections.
• Inspect wiring harnesses to the Coil/Injector for abrasion or damage.

Swap-test to identify the faulty component

• Coil swap: Move the Cylinder 4 ignition coil to another cylinder (e.g., Cylinder 1) and observe if the misfire follows the coil. If P0301 appears after swap, the coil is suspect; if P0304 remains, the cylinder-related item (plug, injector, or compression) is more likely.
• Injector swap/test: If you can access the injectors, swap the Cylinder 4 injector with another cylinder’s injector and drive to see if the misfire moves. If it does, the injector is the problem. If the misfire stays on Cylinder 4, injector is fine and you should investigate the other components.
• Spark plug replacement: If you haven’t replaced the cylinder 4 plug yet, do so with a known-good plug of the correct heat range. Re-check for misfire.

Fuel system checks

• Check fuel pressure with a gauge to ensure the rail pressure is within specification for your engine. A weak fuel pump or failing rail regulator can cause misfires if cylinder 4 gets less fuel.
• If equipped, listen for injector click and verify injector wiring pulses using a scan tool with live data.

Air and vacuum diagnostics

• Perform a vacuum test and check for leaks around the intake manifold, especially near Cylinder 4.
• Check MAF and MAP sensors’ readings and ensure they are within spec; a faulty sensor can create an imbalanced air-fuel mixture.

Compression and mechanical checks

• Perform a compression test on Cylinder 4 (and nearby cylinders for comparison). If compression is low, perform a wet compression test (add a small amount of oil to see if compression improves) to differentiate rings/valve problems from head gasket or bore issues.
• If compression is low, assess potential mechanical problems (valve seats, worn rings, head gasket concerns) and plan for further engine service if needed.

Re-check and confirm

• Clear codes after repair and run the engine through a drive cycle to confirm P0304 is cleared and does not reoccur.
• Monitor fuel trims and misfire counters in the scanner to ensure the issue has been resolved.

Notes:

• If P0304 persists after replacing the plug and coil and testing the injector, consider more extensive checks (compression, wiring to the PCM, or possible injector signal issues). In rare cases, a PCM/ECU recalibration or replacement might be indicated, but this is uncommon.

RELATED CODES

• P0300: Random/Multiple Cylinder Misfire Detected
• P0301-P0308: Cylinder-specific misfire codes (P0301 = Cylinder 1, P0302 = Cylinder 2, etc.)
• P1300-P1303: Catalytic converter or misfire-related codes may appear if misfire continues and affects emissions.
• Note: For diagnostic clarity, address P0304 first; if other misfire codes appear, follow the same diagnostic sequence for the corresponding cylinder(s).

REPAIR OPTIONS AND COSTS (2025 prices)

Prices are rough estimates for typical U.S. shops and can vary by region, labor rate, and specific engine configuration in the 2021-2024 Ford F-150.

Option A – Cylinder 4 spark plug replacement (plus inspection)

• Parts: Spark plug for Cylinder 4 (OEM or equivalent): $10–$40
• If you replace all 8 plugs as preventive maintenance: $80–$320
• Labor: 0.3–1.0 hours (depending on engine and access)
• Labor cost: $40–$180 (assuming shop rate $100–$180/hr)
• Estimated total: $50–$520 (single plug) or $200–$520 (all plugs)

Option B – Cylinder 4 ignition coil replacement

• Parts: Ignition coil (COP) for Cylinder 4: $60–$180
• Labor: 0.2–0.8 hours
• Labor cost: $25–$150
• Estimated total: $85–$330

Option C – Cylinder 4 fuel injector cleaning or replacement

• Fuel injector cleaning (maintenance service): $50–$150 (if cleaning is possible; cheaper than replacement)
• Parts (new injector): $150–$350
• Labor: 0.5–2.0 hours
• Labor cost: $60–$360
• Estimated total: $110–$710 (replacement likely higher)

Option D – Fuel system or vacuum leak repair (if a leak or restricted path is found)

• Parts: Vacuum hose or intake gasket: $10–$100
• Labor: 0.5–2.0 hours
• Labor cost: $60–$360
• Estimated total: $70–$460

Option E – Compression/valve issue correction (if mechanical problem found)

• Minor fixes (valve seal, gasket, minor head work): $500–$1500
• Major repairs (valve job, bore/ piston work, head resurfacing): $1500–$5000+
• This range covers a broad scope and can be significantly higher if major components are involved.

Option F – Comprehensive diagnostic and repair when multiple causes are suspected

• Diagnostic labor: 1.0–2.5 hours
• Diagnostic charges commonly apply even if you later perform repairs
• Estimated total: $120–$450 (diagnostic only, depending on shop)

Important notes about costs:

• Prices vary by region, shop, engine variant (2.7L EcoBoost, 3.5L EcoBoost, 5.0), and whether you replace one component or perform preventive maintenance (e.g., replacing all spark plugs at once).
• If multiple cylinders show misfires or if you find a common cause (like a failing ignition coil boot or a faulty injector on the same bank), the cost can be lower per-cylinder when components are replaced together.

DIY VS PROFESSIONAL

• Do-it-yourself (DIY) feasible for skilled hobbyists:
  • Replacing a single spark plug on most Ford F-150 engines (especially with good access) and swapping a coil on some layouts are workable for DIYers with basic tools and torque knowledge.
  • Basic tester checks (visual inspection, spark plug look, coil swap test, and simple fuel pressure checks with a gauge) can be attempted by capable DIYers.
• Professional service recommended for:
  • Access-limited plug/coil replacement on certain engine configurations (e.g., 3.5L EcoBoost or 5.0L with tight engine bays).
  • Injector testing or replacement, fuel system testing, and precise fuel trim analysis.
  • Compression testing, leak-down tests, or potential mechanical engine issues.
  • If you suspect PCM/ECU issues or when misfire persists after simple fixes.
• Safety and tools:
  • Relieve fuel pressure before disconnecting fuel lines or rails.
  • Disconnect the battery before service on coil packs or the PCM wiring to avoid shorts.
  • Use proper torque specs when tightening plugs/coil fasteners (consult the service manual).
  • Always clear codes and perform a test drive after repairs to confirm the fix.

PREVENTION

• Regular maintenance according to Ford’s schedule:
  • Replace spark plugs at manufacturer-recommended intervals with the correct heat range and torque.
  • Replace ignition coils only as required or if a misfire persists after plug replacement.
  • Keep the air filter clean and ensure the MAF sensor is functioning properly.
  • Use high-quality fuel and avoid contaminated fuel; consider fuel system cleaners only as recommended by Ford or your technician.
  • Maintain fuel pressure and inspect the fuel delivery system if you notice a pattern of misfires.
  • Periodically inspect vacuum hoses for cracks or leaks and address any leaks promptly.
• Battery and charging system: Ensure a healthy battery and stable voltage; poor ignition energy can contribute to misfires.
• If you’ve had misfires in cylinder 4, consider proactive coil/plug replacement in line with maintenance schedule to reduce future risk.

Data and limitations

• The provided data indicates no NHTSA owner complaints for this exact 2021-2024 Ford F-150 P0304 combination.
• The data also shows no recalls found in the NHTSA database for this combination.
• The guide uses general automotive knowledge and standard diagnostic practices. Actual vehicle behavior can vary by engine variant, trim, and aftermarket modifications.
• Always verify with current manufacturer service information for your exact engine (2.7L EcoBoost, 3.5L EcoBoost, 5.0 V8) and your VIN, as there can be model-year or engine-family specific nuances.