P0304 on 2024-2025 Lincoln Nautilus: Cylinder 4 Misfire Causes and Fixes

What's Unique About the 2024-2025 Lincoln Nautilus

The 2024-2025 Nautilus uses a 2.0L EcoBoost engine. While P0304 is often a simple ignition issue, this engine family has a widely documented history of a serious design flaw in pre-2019 models that allowed coolant to leak into the cylinders, causing misfires. This was caused by coolant passages between cylinders that were too large, compromising the head gasket seal. Crucially, engines built for the 2024-2025 Nautilus feature a redesigned engine block with smaller 'pinhole' coolant passages to prevent this specific failure. Lincoln has already issued Technical Service Bulletins for the 2024-2025 Nautilus with misfire codes (P0301-P0304), indicating a known issue the manufacturer is tracking and pointing towards spark plugs and coils as the primary culprits.

Symptoms You May Notice

• Rough or shaky idle
• Hesitation or stumbling during acceleration
• Noticeable loss of engine power
• Flashing Check Engine Light (in cases of severe misfire)
• Reduced fuel economy
• Unpleasant fuel odor from the exhaust

Most Likely Causes

1. Faulty Ignition Coil 🔴 High Probability → Shop Ignition Coil Manufacturer Technical Service Bulletin (TSB) SSM 53971 directly points to ignition coils as a primary culprit for P0301-P0304 misfires on the 2024-2025 Nautilus with the 2.0L EcoBoost engine. This is a very common failure point for single-cylinder misfires on modern engines.
   How to confirm: Swap the ignition coil from cylinder 4 with another cylinder (e.g., cylinder 3). Clear the codes and drive. If the misfire code changes to P0303, the coil is faulty. 🎬 Watch: How to troubleshoot and test for a cylinder 4 misfire.
   Typical fix: Replace the faulty ignition coil. It is often recommended to replace all four as a set if they are original.
   Est. part cost: $40-$115
2. Worn or Defective Spark Plug 🔴 High Probability → Shop Spark Plug TSBs 25-2074 and SSM 52419 explicitly state that misfire codes on the 2024 Nautilus may be due to spark plugs and direct technicians to inspect them first as the primary action. These bulletins cover the Nautilus and its platform mates, the Lincoln Corsair and Ford Escape.
   How to confirm: Remove the spark plug from cylinder 4 and inspect it for wear (worn electrode), damage (cracked porcelain), or fouling (covered in oil or carbon). You can also swap it with another cylinder's spark plug to see if the misfire follows.
   Typical fix: Replace the spark plug in cylinder 4. Best practice is to replace all four spark plugs as a set to ensure even performance. The correct gap is 0.027 - 0.031 inches. 🎬 See these two simple DIY methods to fix the P0304 code.
   Est. part cost: $10-$30
3. Faulty Fuel Injector ⚪ Low Probability → Shop Fuel Injector While less common than ignition issues, direct injection systems can be susceptible to carbon buildup or electronic failure over time, leading to a misfire.
   How to confirm: This is more advanced. A professional can perform a power balance test with a scan tool to confirm the injector isn't firing. One can also listen for a clicking sound from the injector with a mechanic's stethoscope.
   Typical fix: Replace the fuel injector for cylinder 4. This is a more involved job than a coil or plug.
   Est. part cost: $50-$150

Rare But Worth Checking

• Internal Engine Mechanical Problem: While the notorious coolant intrusion issue of older 2.0L EcoBoost engines was addressed with a block redesign, TSB 25-2074 for the 2024-2025 Nautilus still outlines a procedure for a borescope inspection of the cylinder walls and pistons if a damaged spark plug is found. This suggests that although rare, internal damage (such as scored cylinder walls) is still a possibility that Ford requires technicians to investigate if initial ignition-related fixes fail.

Diagnosis Steps

1. Read the code using an OBD-II scanner and check for any other stored codes.
2. Perform the 'coil swap' test: Label and swap the ignition coil from cylinder 4 with a coil from another cylinder (e.g., cylinder 1).
3. Clear the codes and drive the vehicle to see if the check engine light returns.
4. Re-read the codes. If the code has moved to P0301, the ignition coil is the problem.
5. If the code remains P0304, the coil is likely good. Put the coils back in their original positions.
6. Perform the 'spark plug swap' test: Swap the spark plug from cylinder 4 with the plug from another cylinder (e.g., cylinder 2).
7. Clear codes and drive. If the code changes to P0302, the spark plug is the problem.
8. If the code remains P0304, and the plugs and coils are confirmed good, the issue may be the fuel injector or a mechanical engine problem. Per TSB 25-2074, a professional should inspect for loose PCM ground circuits or use a borescope to check for internal cylinder damage.

Parts You'll Likely Need

• Ignition Coil (OEM #JX6Z-12029-B or P2GZ-12029-A) — This is one of the most common failure points for a single-cylinder misfire and is identified as a likely cause in manufacturer TSBs for this vehicle. Note: Part number JX6Z-12029-B is specified for models built up to 5/13/2024, while P2GZ-12029-A is listed for models built after. Always verify by VIN. 🎬 Watch this walkthrough on replacing spark plugs and coils.
  Trusted brands: Motorcraft, Denso, NGK
  OEM price range: $60-$115
  Aftermarket price range: $40-$80
• Spark Plug (OEM #SP-597-X (Motorcraft)) — Spark plugs are a regular maintenance item. TSBs 25-2074 and SSM 52419 specifically call for their inspection and replacement to fix misfires on this vehicle. The part number JYSP-12Y-PTX may also be used.
  Trusted brands: Motorcraft, NGK
  OEM price range: $15-$30
  Aftermarket price range: $10-$25

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or begins to affect other cylinders, a P0300 (Random/Multiple Cylinder Misfire) may be stored.
• P0316 — This code indicates a misfire was detected on startup (within the first 1,000 revolutions). It's often seen with P0304, especially if an issue causes the spark plug to be fouled on a cold start.
• P0301, P0302, P0303 — If other cylinder-specific misfire codes appear, it points towards a problem affecting the whole engine, such as a vacuum leak or low fuel pressure, rather than a single component on cylinder 4.

Technical Service Bulletins (TSBs) & Recalls

• TSB 25-2074: Supersedes earlier bulletins (like 24-2384) and applies to 2024-2025 Nautilus models with the 2.0L EcoBoost. It outlines the official diagnostic procedure for P0301-P0304 misfires, starting with spark plug inspection and escalating to a borescope check for internal engine damage if necessary.
• SSM 52419: An earlier Special Service Message advising technicians that 2024 Nautilus vehicles may exhibit misfire codes (P0301-P0304) and to inspect the condition of all spark plugs. It also mentions that if cylinder walls are scored, a long block replacement is required.
• SSM 53971: A Special Service Message that includes the 2024-2025 Nautilus and other models, pointing to spark plugs and/or ignition coils as the likely cause for P0301-P0304 misfires and directing technicians to standard workshop manual diagnostics.

Platform-Specific Known Issues

• TSB 25-2074 / SSM 52419: Ford has issued bulletins for the 2024-2025 Nautilus specifically for misfire codes P0301-P0304, directing technicians to inspect spark plugs and ignition coils as the primary diagnostic step. The TSB also includes advanced diagnostics like checking PCM grounds and performing a borescope inspection for cylinder damage if plugs are found to be damaged.
• Resolved Coolant Intrusion Design: Unlike pre-2020 2.0L EcoBoost engines, the engine in the 2024-2025 Nautilus has a redesigned block that is not prone to the infamous coolant intrusion head gasket failure that caused misfires on older models.

Mechanic-Grade Diagnostic Values

• Ignition Coil Primary Resistance — expected: 0.52 - 0.64 Ohms. Failure: A reading outside this range, or an open circuit (infinite resistance), points to a faulty coil.
• Ignition Coil Secondary Resistance — expected: 6.6k - 7.9k Ohms. Failure: A reading outside this range suggests a failure in the coil's secondary windings.
• Low-Pressure Fuel System (LPFP) — expected: Approximately 45 - 75 PSI at idle/KOER (Key On, Engine Running).. Failure: Pressure significantly below this range may indicate a failing in-tank fuel pump or a clogged fuel filter, leading to lean conditions.
• High-Pressure Fuel System (HPFP) — expected: 200 - 800 PSI at idle, rising to over 2,000 PSI under load.. Failure: If the scan tool's 'Desired Fuel Rail Pressure' is high but the 'Actual Fuel Rail Pressure' remains low, it often points to a failing HPFP or a worn camshaft lobe that drives it.

Hidden / Shadow Codes Worth Checking

• Mode $06, Test ID $A5: This is not a trouble code, but an onboard monitor for the misfire count on cylinder 4. Advanced scanners can display this data to show how many misfire events the PCM has detected in the current and previous 10 drive cycles. A high count confirms the misfire, even if the Check Engine Light isn't on. (see via An advanced OBD-II scanner or software (like FORScan) that can display Mode $06 test results.)

Scan Tool Commands That Help

• Ford IDS (or equivalent high-level scanner): Power Balance Test — This is a crucial test to confirm a misfire and isolate the cylinder. The tool graphically displays the RPM drop from each cylinder and allows the technician to disable individual fuel injectors to see the effect on engine speed. A cylinder that shows little to no RPM drop when its injector is disabled is the source of the misfire.
• Ford IDS (or equivalent high-level scanner): Misfire Monitor Neutral Profile Correction — This procedure MUST be performed after major engine or transmission repairs, such as replacing a crankshaft sensor, timing components, or the PCM itself. The PCM 'learns' the signature of the crankshaft, and failing to run this relearn procedure can cause the PCM to falsely detect misfires and set codes like P0304.

Wiring & Ground Locations

• C1584 — Engine, top LH side, connector for ignition coil on cylinder 4.. This is the direct electrical connector for the ignition coil on the misfiring cylinder. Checking for voltage, ground, and signal integrity at this connector is a key diagnostic step. The pinout is typically Pin 1 (Control Signal from PCM), Pin 3 (Ground), and Pin 4 (12V Power).
• Negative Battery Cable to Ground — In the loadspace/trunk area, under the floor covering and storage bin, near the 12V battery.. While not a primary cause, a poor main battery ground can cause a host of difficult-to-diagnose electrical issues, including weak spark. The official first responder guide shows the exact location of this critical ground point.
• Engine Compartment Fuse Box — Located near the battery under the hood.. This box contains the fuses and relays for the ignition coils and fuel injectors. A faulty fuse or relay for the ignition or fuel systems could cause a no-spark or no-fuel condition leading to a misfire.

Model Year Variations Within This Range

• 2024: The ignition coil part number changed during the 2024 model year. Models built up to 5/13/2024 use part number JX6Z-12029-B, while models built after use P2GZ-12029-A. This indicates a potential design revision or supplier change that could affect performance or longevity. Always verify the correct part number by VIN.

Diagnostic Flowchart

Related OBD-II Codes

• P0301 — Cylinder 1 Misfire Detected. Explicitly grouped with P0304 in TSB 25-2074, SSM 52419, and SSM 53971 as part of the known spark plug and ignition coil issues on the 2.0L EcoBoost.
• P0302 — Cylinder 2 Misfire Detected. Explicitly grouped with P0304 in TSB 25-2074, SSM 52419, and SSM 53971 as part of the known spark plug and ignition coil issues on the 2.0L EcoBoost.
• P0303 — Cylinder 3 Misfire Detected. Explicitly grouped with P0304 in TSB 25-2074, SSM 52419, and SSM 53971 as part of the known spark plug and ignition coil issues on the 2.0L EcoBoost.
• P0300 — Random/Multiple Cylinder Misfire Detected. Often appears alongside specific cylinder misfire codes (P0301-P0304) if multiple spark plugs or coils are failing simultaneously, as outlined in the related TSBs.

Frequently Asked Questions