P0304 on 2016-2017 Lincoln MKX: Cylinder 4 Misfire Causes and Fixes

What's Unique About the 2016-2017 Lincoln MKX

For the 2016-2017 Lincoln MKX equipped with the optional 2.7L EcoBoost V6, a P0304 code can be more than a simple ignition fault. Manufacturer Technical Service Bulletins (TSBs), including SSM 54504 and TSB 19-2384, directly connect this misfire code to a more severe problem involving excessive oil consumption. This condition is often caused by defective cylinder head valve guides, which allows oil to enter the combustion chamber, foul the spark plug, and cause a misfire. This makes the diagnosis much more significant than a typical spark plug or coil replacement. Owners of the 3.7L V6 are more likely to experience common ignition or fuel system faults, though accessing the rear bank of spark plugs requires removing the intake manifold.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Rough idle or shaking
• Hesitation or stumbling during acceleration
• Flashing or solid Check Engine Light
• Reduced engine power
• Poor fuel economy
• Smell of unburned gasoline from the exhaust
• White or blue smoke from the exhaust (especially on 2.7L V6)
• Excessive oil consumption (2.7L V6)

Most Likely Causes

1. Faulty Ignition Coil 🔴 High Probability → Shop Ignition Coil Coil-on-plug systems are a common failure point on modern engines due to constant exposure to heat and vibration.
   How to confirm: Swap the ignition coil from cylinder 4 with another cylinder (e.g., cylinder 5). Cylinder 4 is the front-most cylinder on the driver's side. Clear the codes and drive. If the code changes to P0305, the ignition coil is faulty.
   Typical fix: Replace the failed ignition coil. It is best practice to also replace the spark plug at the same time. 🎬 Watch: Step-by-step guide to replacing spark plugs and ignition coils.
   Est. part cost: $40-$90
2. Worn or Fouled Spark Plug 🔴 High Probability → Shop Spark Plug
   How to confirm: Remove the spark plug from cylinder 4. Inspect it for wear (worn electrode), carbon fouling (black and sooty), oil fouling (wet and black), or coolant fouling (white, steam-cleaned appearance). On the 2.7L V6, oil fouling is a strong indicator of the TSB-related cylinder head issue.
   Typical fix: Replace the spark plug. If all plugs are near the end of their service life, replace them as a set. For the 3.7L V6, accessing the rear three plugs requires removing the upper intake manifold. 🎬 See how to remove the intake manifold on the 3.7L V6.
   Est. part cost: $10-$25
3. Cylinder Head Issue / Excessive Oil Consumption (2.7L V6) 🟡 Medium Probability → Shop Engine Cylinder Head As documented in TSBs like 19-2384 (which supersedes earlier versions), some 2.7L V6 engines built between April 2016 and January 2017 have defective cylinder head valve guides. This allows oil to leak into the cylinder, causing smoke, oil consumption, and misfires.
   How to confirm: Monitor engine oil levels closely. If the vehicle consumes more than 1 quart of oil in less than 3,000 miles, this is the likely cause. A professional diagnosis involving a cylinder leak-down test is the definitive confirmation.
   Typical fix: This is a major repair that requires professional service and involves replacing both cylinder heads per the manufacturer's TSB.
   Est. part cost: $2000-$5000+
4. Faulty Fuel Injector ⚪ Low Probability → Shop Fuel Injector
   How to confirm: This is more difficult to diagnose. A professional can perform a fuel injector balance test. A DIY method is to listen to the injector with a mechanic's stethoscope; it should have a consistent clicking sound. You can also swap injectors between cylinders, but this is labor-intensive.
   Typical fix: Replace the faulty fuel injector.
   Est. part cost: $70-$150

Rare But Worth Checking

• Vacuum Leak: A vacuum leak near the intake manifold runner for cylinder 4 can lean out the air-fuel mixture and cause a misfire on just that cylinder. This could be from a failed intake manifold gasket.
• Low Engine Compression: Internal engine mechanical problems like a worn piston ring, a damaged valve, or a failing head gasket can cause a loss of compression and a persistent misfire. A compression test is needed to diagnose this.

Diagnosis Steps

1. Read the code with an OBD-II scanner and note any other codes present.
2. Identify the engine (3.7L V6 or 2.7L EcoBoost V6).
3. Locate Cylinder 4. On both the 3.7L and 2.7L transverse-mounted engines, the cylinder banks are arranged with Bank 1 (cylinders 1-2-3) against the firewall and Bank 2 (cylinders 4-5-6) at the front of the vehicle. Cylinder 4 is the cylinder closest to the driver's side on the front bank.
4. If the engine is the 2.7L V6, check the engine oil level immediately. If low, top it off and monitor for excessive consumption (more than 1 quart per 3,000 miles).
5. Swap the ignition coil from cylinder 4 to an adjacent cylinder (e.g., cylinder 5). Clear the codes and see if the misfire code moves to the new cylinder (e.g., P0305). If it does, the coil is bad.
6. If the misfire does not move, inspect the spark plug from cylinder 4. Look for signs of wear, damage, or fouling (especially oil fouling on the 2.7L). Replace if necessary.
7. If ignition parts are good and oil consumption is suspected (2.7L V6), the vehicle should be taken for professional diagnosis, referencing TSB 19-2384 or SSM 54504.
8. Check the wiring and connector for the ignition coil and fuel injector on cylinder 4 for any damage or loose connections.
9. If all else fails, a professional should perform a compression test and a cylinder leak-down test to check for mechanical engine health.

Parts You'll Likely Need

• Ignition Coil (2.7L V6) (OEM #FT4Z-12029-A) — This is one of the most common failure points for a single-cylinder misfire.
  Trusted brands: Motorcraft, NGK, Denso
  OEM price range: $60-$100
  Aftermarket price range: $40-$80
• Ignition Coil (3.7L V6) (OEM #7T4Z-12029-E) — A common failure point for an isolated cylinder misfire on the naturally aspirated V6.
  Trusted brands: Motorcraft, Delphi, NGK
  OEM price range: $60-$100
  Aftermarket price range: $35-$75
• Spark Plug (2.7L V6) (OEM #SP-594 (Motorcraft)) — Spark plugs are a routine maintenance item and can foul or wear out, causing a misfire. On the 2.7L, they can become oil-fouled due to the cylinder head issue.
  Trusted brands: Motorcraft, NGK
  OEM price range: $15-$30
  Aftermarket price range: $8-$20
• Spark Plug (3.7L V6) (OEM #CYFS-12Y-2 (Motorcraft)) — Spark plugs are a wear item and a primary cause of misfires.
  Trusted brands: Motorcraft, NGK, Champion
  OEM price range: $10-$20
  Aftermarket price range: $5-$15

Related Codes That Often Appear With This One

• P0300 — If the underlying issue begins to affect other cylinders, a random misfire code may be stored. This is common with the 2.7L V6 oil consumption issue.
• P0301, P0302, P0303, P0305, P0306 — These codes indicate misfires in other cylinders. Seeing them with P0304 points to a systemic issue like a vacuum leak or the cylinder head problem described in the TSBs.
• P0316 — Indicates a misfire detected on startup (first 1000 revolutions). This is specifically mentioned in the TSBs as a related code, as oil that has seeped into the cylinder overnight will cause an immediate misfire.
• P0524, P06DD — These codes indicate low engine oil pressure or a fault in the oil pressure control circuit. Their presence alongside P0304 on a 2.7L V6 strongly suggests the oil consumption issue has become severe enough to starve the oil pump, potentially leading to catastrophic engine damage.

Technical Service Bulletins (TSBs) & Recalls

• SSM 54504: Links misfire DTCs P0300-P0306 with excessive oil consumption and oil pressure codes P0524/P06DD, identifying valve guides as the cause.
• SSM 46363: An earlier bulletin suggesting cylinder heads may be the cause

Platform-Specific Known Issues

• On 2.7L V6 engines, TSB SSM 46363 notes that misfire codes (P0300-P0306) can be caused by a cylinder head issue, which may also present with a rough idle and excessive oil consumption.
• TSB SSM 54504 expands on this, linking misfire codes P0300-P0306 and P0316 with excessive oil consumption (1 quart in less than 3,000 miles) and potential oil pressure codes P0524 and/or P06DD. It identifies the cause as a concern with the valve guides.
• TSB 19-2384, which supersedes earlier bulletins for the F-150 with the same engine, details the full repair procedure, which involves replacing both left and right cylinder heads.

Mechanic-Grade Diagnostic Values

• Low-Side Fuel Pressure (2.7L EcoBoost) — expected: 51 – 87 psi (350 – 600 kPa) with engine running.. Failure: Pressure below this range can cause lean misfires under load.
• Spark Plug Gap (3.7L V6) — expected: 1.25 - 1.35 mm (0.049 - 0.053 in.).. Failure: An incorrect gap can lead to a weak spark and incomplete combustion.

Hidden / Shadow Codes Worth Checking

• Mode 6, Test ID $80-$83: This is not a DTC, but a diagnostic test monitor for misfires. Advanced scan tools can access this data to view the raw misfire count for each cylinder over the current and last 10 drive cycles, even if the count is not high enough to trigger a P0304 code. (see via Requires a scan tool capable of reading Mode 6 data, such as Ford's IDS, FORScan, or other professional-grade scanners.)

Scan Tool Commands That Help

• Ford IDS (or equivalent high-end scanner): Misfire Monitor Neutral Profile Correction — This procedure is critical after any major engine or transmission repair, such as engine replacement. It relearns the crankshaft position sensor's profile to prevent the PCM from falsely detecting misfires due to subtle changes in crankshaft rotation. Failure to perform this can cause persistent, difficult-to-diagnose misfire codes like P0304.
• Ford IDS (or equivalent high-end scanner): Power Balance Test — This bidirectional test allows the technician to disable one cylinder at a time (by cutting fuel or spark) and observe the corresponding drop in RPM. If disabling cylinder 4 causes little or no change in RPM, it confirms that cylinder is not contributing power.

Wiring & Ground Locations

• Engine Compartment Fuse Box (Power Distribution Box) — Located in the front left area of the engine bay, near the battery.. This box contains fuses and relays for the ignition system and the Powertrain Control Module (PCM). A loose or corroded connection here can cause intermittent power loss to the ignition coils.
• Main Chassis Ground — A primary ground stud is located on the front of the driver's side strut tower, to the right of the battery.. The ignition coils require a solid ground path to function correctly. A poor ground connection at this point can introduce electrical resistance and cause a weak spark, leading to misfires.

Model Year Variations Within This Range

• 2016-2017 (2.7L V6): Models with the 2.7L V6 built between approximately April 2016 and January 2017 are specifically implicated in TSBs regarding excessive oil consumption due to cylinder head issues, which directly cause misfire codes like P0304. Vehicles outside this build range are less likely to have this specific defect.
• 2016-2017 (2.7L V6): These model years are equipped with the first-generation plastic oil pan, which was prone to developing leaks at the sealant surface. While not a direct cause of P0304, a significant oil leak could lead to low oil levels, which are associated with the more severe engine problems that do cause misfires.