P0308 on 2021-2025 Ford E-Series 7.3L V8: Cylinder 8 Misfire Causes and Fixes

What's Unique About the 2021-2025 Ford E-Series (E-350/E-450)

For most engines, a P0308 code points to a simple tune-up part. On the 7.3L 'Godzilla' V8, however, this code has two very different common causes with vastly different repair implications. The first is a well-documented weakness in the factory spark plug wires, which are prone to failing from high heat near the exhaust manifolds. The second is a much more serious, known issue of premature camshaft and valve lifter (tappet) failure. This internal engine failure is often preceded by a distinct ticking noise. Ford has acknowledged both issues in technical service bulletins (TSB 20-2370 for wires, TSB 23-2250 and others for lifters), making a careful diagnosis critical to distinguish between a simple fix and a major engine repair.

Symptoms You May Notice

• Rough or shaking idle
• Engine stumbling or hesitating during acceleration
• Flashing Check Engine Light (indicates a severe misfire)
• Noticeable loss of engine power
• Audible ticking or tapping noise from the engine (a key indicator of potential mechanical lifter/cam failure)

Most Likely Causes

1. Faulty Spark Plug Wire 🔴 High Probability The original equipment spark plug wires on the 7.3L V8 are a known weak point, frequently failing due to high heat from the nearby exhaust manifolds. Ford acknowledged this issue and released updated, more robust wires. TSB 20-2370 was issued for the F-53 motorhome chassis for this exact problem, which is common across all 7.3L applications.
   How to confirm: Swap the spark plug wire from cylinder 8 with another cylinder (e.g., cylinder 6). Clear the codes and drive. If the misfire code changes to P0306, the wire is bad. You can also visually inspect the wire and boot for any signs of arcing (white marks), burning, or brittleness. A 'water mist test' (spraying a fine mist of water on the wire with the engine running) may reveal arcing.
   Typical fix: Replace the full set of 8 spark plug wires with the updated OEM Motorcraft parts or high-quality aftermarket wires designed for high-temperature environments. Do not replace with the original-spec part.
   Est. part cost: $100-$160 for a full set of updated wires.
2. Failed Camshaft and/or Valve Lifter (Tappet) 🟡 Medium Probability This engine family has a widely documented issue with premature valvetrain wear, where the surface of a lifter roller can delaminate or 'spall', destroying the camshaft lobe. Ford has issued multiple TSBs (like 23-2250 and others) acknowledging this failure. The issue is believed to be exacerbated by the original PCM software which allowed for very low oil pressure at idle; Ford later issued Customer Satisfaction Program 24B27 to reprogram the PCM to increase this pressure.
   How to confirm: The primary symptom is a persistent misfire accompanied by an audible ticking or tapping noise from the engine's upper or lower end. A definitive diagnosis requires a compression test on cylinder 8; a low reading points towards this mechanical failure. Further confirmation involves inspecting the oil and oil filter for metal debris and, ultimately, internal engine inspection by a professional.
   Typical fix: This is a major engine repair that involves replacing the camshaft, all 16 valve lifters, and any other damaged components. Due to the risk of metal contamination throughout the engine, many dealerships and owners opt for a complete long block engine replacement, especially if under warranty.
   Est. part cost: $1500-$8000+
3. Faulty Ignition Coil 🟡 Medium Probability
   How to confirm: Swap the ignition coil from cylinder 8 with another cylinder (e.g., cylinder 7). Clear the codes and drive. If the code changes to P0307, the ignition coil is bad.
   Typical fix: Replace the single faulty ignition coil. They are mounted near the valve cover and are easily accessible.
   Est. part cost: $40-$70
4. Worn or Fouled Spark Plug ⚪ Low Probability
   How to confirm: After ruling out the wire and coil, remove the spark plug from cylinder 8. Inspect it for heavy carbon buildup, oil fouling, or a worn-out electrode. Compare it to a new plug.
   Typical fix: Replace the spark plug. It is often recommended to replace all 8 plugs at the same time for consistent performance.
   Est. part cost: $10-$25 per plug

Rare But Worth Checking

• Faulty Fuel Injector: Less common than ignition or mechanical issues, but can cause an identical misfire. Diagnosis involves listening for the injector's click with a stethoscope or having a professional test its function with a scan tool.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0308 and check for any other codes like P0300 or P0316.
2. Listen carefully to the engine at idle. Is there a distinct ticking or tapping noise? If yes, the probability of a serious mechanical issue (lifter/cam failure) is extremely high. Proceed to step 6 and prepare for professional diagnosis.
3. If no ticking is present, begin with the most common failure: the ignition system. Swap the spark plug wire from cylinder 8 (rearmost, driver's side) with the wire from cylinder 6. Clear codes and test drive. If the code moves to P0306, the wire is faulty. Replace the full set with updated parts.
4. If the code remains P0308, swap the ignition coil from cylinder 8 with the coil from cylinder 7. Clear codes and test drive. If the code moves to P0307, the coil is faulty.
5. If the code still remains P0308, inspect the spark plug for wear or fouling. Replace if necessary.
6. If ignition parts are confirmed good (or if a ticking noise was present from the start), a mechanical issue is the next logical step. Perform an engine compression test on cylinder 8. A significantly low reading strongly suggests a valvetrain problem.
7. If compression is low, inspect the engine oil and cut open the oil filter to look for metallic debris, a hallmark of lifter/cam failure. At this point, the vehicle should be taken to a qualified technician.
8. If compression is good, the final step is to investigate the fuel injector for cylinder 8.

Parts You'll Likely Need

• Ignition Wire Set (Set of 8, Upgraded Design) (OEM #LC3Z-12286-C or LC3Z-12286-D) — This is the most common failure point for a P0308 code on this engine due to heat degradation. The -C and -D revisions are the redesigned, more robust parts intended to fix the issue permanently.
  Trusted brands: Motorcraft
  OEM price range: $120-$160
  Aftermarket price range: $100-$200
• Ignition Coil (OEM #LC3Z-12029-A (Motorcraft DG592)) — The second most likely ignition component to fail, causing a misfire on a single cylinder.
  Trusted brands: Motorcraft, NGK, Delphi
  OEM price range: $50-$70
  Aftermarket price range: $35-$60
• Spark Plug (OEM #SP-580 (CYFS-12Y-9)) — A standard maintenance item that can wear out and cause a misfire.
  Trusted brands: Motorcraft, NGK
  OEM price range: $12-$20
  Aftermarket price range: $8-$15
• Camshaft and Lifter Kit (OEM #Camshaft: PC3Z-6250-A; Lifters/Tappets: LC3Z-6500-C) — Required for the known catastrophic mechanical failure. This is not a simple parts replacement and often results in a full engine replacement under warranty.
  Trusted brands: Motorcraft
  OEM price range: $1000-$2500
  Aftermarket price range: $800+

Related Codes That Often Appear With This One

• P0300 — If the misfire becomes more widespread due to a systemic issue like a vacuum leak or a progressing valvetrain problem, a P0300 (Random/Multiple Cylinder Misfire) code may appear alongside P0308.
• P0316 — This code indicates a misfire was detected within the first 1,000 engine revolutions on startup. It often accompanies a specific cylinder misfire code like P0308 and is specifically mentioned in TSB 20-2370 regarding faulty plug wires.

Technical Service Bulletins (TSBs) & Recalls

• TSB 20-2370: Addresses misfires on F-53 chassis due to heat-damaged spark plug wires.
• TSB 23-2250: Links engine tick/knock and P0300-P0308 codes to failed valve tappet rollers.
• TSB 25-2572: Also links P030x codes to excessive camshaft and/or valve tappet (lifter) wear.
• Customer Satisfaction Program 24B27: PCM software update to increase oil pressure at idle to improve valvetrain lubrication.

Platform-Specific Known Issues

• Spark Plug Wire Failure: The factory-installed spark plug wires are known to become brittle and fail due to high heat from the exhaust manifolds, causing misfires. This was the subject of TSB 20-2370 for F-53 applications and is a widely reported issue across all platforms using this engine. Ford has released redesigned wires (part numbers ending in -C or -D) that are more heat resistant.
• Camshaft/Lifter Failure: A significant number of 7.3L 'Godzilla' engines have experienced premature failure of the valve lifters (tappets), which in turn destroys the camshaft lobes. This causes a persistent misfire and a distinct ticking/tapping noise. This issue is acknowledged in multiple TSBs (e.g., 25-2572) and was addressed in production with updated lifter designs around the 2023 model year. A related Customer Satisfaction Program (24B27) was also issued to reprogram the PCM to increase oil pressure at idle, which is believed to be a contributing factor to the wear.

Mechanic-Grade Diagnostic Values

• Fuel Injector Coil Resistance — expected: 11.0 - 18.0 Ohms. Failure: A reading outside this range indicates a faulty injector coil winding.
• Ignition Coil Primary Resistance — expected: ~0.53 Ohms. Failure: Significant deviation from this value suggests a fault in the primary winding.
• Ignition Coil Secondary Resistance — expected: ~4.8K - 13.7K Ohms. Failure: A reading far outside this range points to an internal failure of the secondary coil winding.
• Fuel Pressure (Key On, Engine Running) — expected: 55 - 60 psi. Failure: Pressure significantly below this range could indicate a weak fuel pump or a failing in-tank regulator.
• OBD-II Mode $06, Test ID $A9 (Cylinder 8 Misfire Count) — expected: A count near zero for the current and last 10 driving cycles.. Failure: A high or rapidly increasing count confirms cylinder 8 is misfiring, even if the Check Engine Light is not yet on. This is invaluable for diagnosing intermittent issues.

Hidden / Shadow Codes Worth Checking

• Mode $06, Test ID $A9, Component ID $08: This is not a traditional DTC, but a specific monitor within the OBD-II system that provides raw misfire counts for cylinder 8. It allows a technician to see intermittent misfires that have not yet met the threshold to trigger a P0308 code. (see via An advanced scan tool or software like FORScan that can display OBD-II Mode $06 data.)

Scan Tool Commands That Help

• Ford IDS / FORScan: Power Balance Test — This is the primary active test for a misfire. The tool deactivates each cylinder one by one and graphically displays the RPM drop. A cylinder (like #8) with a minimal or nonexistent RPM drop is confirmed as the non-contributing, misfiring cylinder.
• Ford IDS / FORScan: Relative Compression Test — After confirming the misfire with a Power Balance test, this command is used to quickly check for a mechanical issue. It measures the electrical current drawn by the starter motor as it cranks the engine through each cylinder's compression stroke. A cylinder with low compression will show a noticeable deviation, pointing towards a mechanical problem like the known lifter/cam failure, without needing to remove spark plugs for a manual test.
• Ford IDS / FORScan: KOEO Injector Electrical Self Test (Buzz Test) — This Key On, Engine Off test commands the PCM to cycle each fuel injector solenoid. It allows a technician to listen for an audible 'buzz' from each injector. A silent or weak-sounding injector on cylinder 8 would indicate a potential electrical fault in the injector itself or its wiring.

Wiring & Ground Locations

• Powertrain Control Module (PCM) Connectors — Typically located in the engine bay, often on the firewall or an inner fender.. The PCM directly controls the ignition coil and fuel injector for cylinder 8. If a misfire persists after swapping known-good components (coil, wire, plug, injector), a technician would perform pin-point voltage and continuity tests at the PCM connector to check for a break or short in the wiring harness between the PCM and the component.
• Main Engine Grounds — Key ground points include straps from the engine block to the chassis frame and from the battery negative terminal to the body and engine.. A poor or corroded engine ground can cause erratic behavior in the ignition system, leading to weak spark and intermittent misfires across multiple cylinders, which could include P0308. Ensuring all main ground connections are clean and tight is a fundamental step in diagnosing electrical issues.

Real Owner Repair Stories

• Commenter on 'Ford F250 7.3L Godzilla Engine Heavy Mechanic Review' YouTube video (2020 Ford F-250 Platinum 7.3L V8, 59,200 miles) — Started with a cylinder #3 misfire code around 50,000 miles. Later developed a loud, distinct tapping noise while towing at 59,200 miles, accompanied by a P0308 code.
  ❌ Tried (didn't work) Replaced all spark plug wires with the latest 'D' revision parts, Replaced all spark plugs, Replaced the ignition coil pack for the affected cylinder
  ✅ What actually fixed it The root cause was diagnosed as the known lifter/camshaft failure. The engine required major internal repairs, which were performed under warranty.
• YouTube video 'FIX!! Ford 7.3 (GAS) ignition wire redesign!' (Ford Super Duty with 7.3L 'Godzilla' Gas engine) — Misfire causing limp mode, popping sounds under acceleration, flashing check engine light.
  ❌ Tried (didn't work) Replacing the failed spark plug wire with the same original OEM part number, which was prone to failing again from heat.
  ✅ What actually fixed it The problem was resolved by replacing the original spark plug wires with the redesigned, more heat-resistant version.

OEM Part Supersession History

• Unknown early-production part numbers → LC3Z-6500-C (Lifter/Tappet) — To address the premature wear and spalling issue causing camshaft failure. Later production engines and service parts feature improved lifter designs.
  Heads up: It is critical to replace all 16 lifters as a set with the updated parts. Mixing old and new designs is not recommended. Aftermarket suppliers like Elgin, Melling, and COMP Cams also offer upgraded replacement lifters.
• LC3Z-12286-A/B → LC3Z-12286-C, then LC3Z-12286-D (Ignition Wire Set) — The original wires were prone to heat degradation from the exhaust manifolds. The 'C' and 'D' revisions are redesigned with better heat shielding and more robust materials to prevent this failure.
  Heads up: The older part numbers will physically fit but are likely to fail again. Always install the latest available revision for a permanent repair.

Model Year Variations Within This Range

• 2020-2022: These earlier model years are more susceptible to the lifter/camshaft failure due to the original lifter design and PCM calibration that allowed for very low idle oil pressure. They also used investment-cast rockers.
• 2023-2025: Starting around 2023, Ford began phasing in updated lifters with improved oil galleries and tighter tolerances to combat the wear issue. The rocker arms were also changed to a stamped steel design. These later engines are considered less prone to the valvetrain failure, but the issue is not entirely eliminated.
• 2020-2025 (All): Ford issued Customer Satisfaction Program 24B27, which involves a PCM software update to increase the Variable Displacement Oil Pump (VDOP) pressure at idle. This can be applied to vehicles across the year range to help mitigate the low oil pressure condition that contributes to lifter wear.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Premature 10R140 Transmission Failure 🔴 High — Reported by some owners, sometimes requiring full replacement before 100,000 miles. Can manifest as harsh or delayed shifting. (Ref: TSB 23-2067 addresses harsh engagement/shifts.)
• Water Intrusion into Battery Junction Box (BJB) 🔴 High — Can occur if the BJB cover is not fully seated or has broken tabs, leading to various electrical issues, no-start conditions, or the engine not turning off. (Ref: TSB 23-2180)
• Variable Displacement Oil Pump Strategy & Lifter Wear 🔴 High — The original PCM calibration allowed for very low oil pressure (as low as 8 psi) at hot idle, which is a suspected contributor to the premature lifter failures. This affects all early-build 7.3L engines. (Ref: Customer Satisfaction Program 24B27 (PCM re-program to increase idle oil pressure))
• Cracked Oil Pump Drive Gear 🟠 Medium — Less common than lifter failure, but can produce a similar ticking/tapping noise from the lower front of the engine at idle. (Ref: SSM 51330)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this specific vehicle and code, using used parts is generally not recommended for the primary failure items. A used ignition coil from a low-mileage donor vehicle could be a viable short-term option if cost is a major concern. However, given the known issues, new parts are strongly advised.

Donor-vehicle mileage cap: roughly under 40000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• For an ignition coil, check for any cracks in the plastic housing or corrosion on the electrical connector.
• Verify the donor vehicle was not involved in a front-end collision that could have damaged engine components.
• Avoid parts from vehicles with high idle hours, as this contributes to the lifter wear issue.

OEM-only on this vehicle (don't cheap out):

• Camshaft and Lifter Kit: Due to the catastrophic nature of the failure and the subsequent design updates, only use the latest revision OEM Motorcraft parts or a reputable performance aftermarket kit specifically designed to solve this problem. Do not use a used camshaft or lifters from a junkyard engine.
• Ignition Wire Set: Do not use used wires. Only install the latest revision OEM Motorcraft set (LC3Z-12286-D or newer) or a high-quality aftermarket set with high-temperature boots.

Aftermarket brands forum-validated for this vehicle:

• Lifter/Cam Kits: Brian Tooley Racing (BTR), COMP Cams, Melling, Johnson Lifters.
• Ignition Wires: MSD, XERAMIK.
• Ignition Coils: NGK, Delphi.

Brands owners have reported issues with on this vehicle:

• Unbranded, 'white box' ignition coils and spark plug wires from online marketplaces should be avoided as their quality and durability are often poor and can cause persistent issues.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0300 — Random or Multiple Cylinder Misfire detection; often appears alongside P0308 when valvetrain wear or spark plug wire heat damage affects multiple cylinders.
• P0316 — Misfire detected on startup (first 1000 revolutions); frequently accompanies P0308 in Godzilla engines experiencing early-stage lifter delamination or fouled plugs.
• P0306 — Cylinder 6 misfire; used during the diagnostic 'swap test' to confirm a faulty spark plug wire or coil moved from cylinder 8.
• P0307 — Cylinder 7 misfire; used during diagnostic steps to verify if a suspected faulty ignition coil from cylinder 8 is the root cause.

Frequently Asked Questions