P0300 on 2017-2021 Ford F-350 SD: Random Misfire Causes & Fixes

What's Unique About the 2017-2021 Ford F-350 SD

The 2017-2021 F-350 Super Duty platform offers a diverse engine lineup, including two gasoline V8s (6.2L 'Boss' and 7.3L 'Godzilla') and the 6.7L Power Stroke diesel V8. This variety means the causes for P0300 can be engine-specific. Ford has issued several Technical Service Bulletins (TSBs) for this generation, pointing to unique issues such as PCM software glitches on the 6.7L diesel (TSB 21-2248), spark plug fouling on the 6.2L in cold weather requiring a PCM update (TSB 18-2188), and a well-documented problem with spark plug wires failing on the 7.3L gas engine (TSB 20-2370). Additionally, early 7.3L engines are known for a serious internal issue with lifter/camshaft failure that can begin as a random misfire.

Diagnostic Flowchart

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

Symptoms You May Notice

• Rough or shaking idle
• Engine hesitation or stumbling during acceleration
• Noticeable loss of power
• Flashing or solid Check Engine Light
• Reduced fuel economy
• Hard starting or extended cranking time
• Popping or backfiring sound under acceleration, especially on the 7.3L V8.
• Audible ticking or tapping noise from the engine, which on a 7.3L V8 could indicate a failing lifter.

Most Likely Causes

1. Faulty Ignition Coils or Spark Plug Wires (Gas Engines) 🔴 High Probability The 7.3L 'Godzilla' engine is notorious for spark plug wire failure due to heat from the exhaust manifolds. TSB 20-2370 was issued for 2020 F-53 chassis models with this engine for damaged wires, confirming it's a recognized issue. The 6.2L and 7.3L gas engines use a coil-on-plug or coil-near-plug design where heat and vibration can cause coils and wires to fail over time.
   How to confirm: For the 7.3L, a common diagnostic trick is to spray a fine mist of water on the spark plug wires in the dark with the engine running; visible arcing indicates a bad wire. For both engines, use a scan tool with live data to view misfire counts per cylinder (Mode $06 data). Swap a suspected bad coil or wire with one from a known good cylinder to see if the misfire follows.
   Typical fix: For the 7.3L, replace all 8 spark plug wires with the updated Motorcraft part (LC3Z-12286-C) or a quality aftermarket set. For the 6.2L, replace the faulty ignition coil(s). It's often recommended to replace all spark plugs at the same time. One owner on YouTube fixed a P0300 on his 2020 7.3L by replacing the wires with an aftermarket set.
   Est. part cost: $70-$150 for a set of wires (7.3L), $40-$70 per coil (6.2L/7.3L).
2. Worn or Fouled Spark Plugs (Gas Engines) 🔴 High Probability Spark plugs are a regular maintenance item. The 6.2L V8 uses 16 spark plugs (two per cylinder), increasing the probability of a failure. TSB 18-2188 (superseding 18-6218) notes that 2017-2018 6.2L engines can suffer from spark plug fuel fouling during cold starts, leading to misfires.
   How to confirm: Remove and inspect the spark plugs. Look for wear on the electrode, carbon buildup, oil fouling, or a smell of fuel. Compare the plugs from misfiring cylinders to those from cylinders that are firing correctly.
   Typical fix: Replace all spark plugs. For the 6.2L, the OEM Motorcraft plug is SP-526-X. For the issue in TSB 18-2188, a PCM reprogram is also required to adjust cold-start fueling.
   Est. part cost: $100-$160 for a set of 16 Motorcraft plugs (6.2L).
3. Faulty Fuel Injectors (Diesel and Gas) 🟡 Medium Probability On the 6.7L Power Stroke, the high-pressure common-rail fuel system operates under extreme pressures, and injectors are a known failure point that can cause misfires. Gas engine injectors can also become clogged or fail electronically.
   How to confirm: For the 6.7L diesel, use a diagnostic scan tool to perform a power balance test to identify a weak or non-contributing cylinder. For gas engines, you can listen for a consistent clicking sound from each injector with a mechanic's stethoscope.
   Typical fix: Replace the faulty fuel injector(s). This is a more complex and expensive job on the 6.7L diesel, often requiring replacement of the high-pressure fuel line to that injector as well.
   Est. part cost: $50-$150 per injector (gas), $300-$500+ per injector (diesel).
4. Vacuum Leak 🟡 Medium Probability Leaking intake manifold gaskets, PCV hoses, or other vacuum lines introduce unmetered air, throwing off the air/fuel ratio and causing random misfires. The large, complex intake systems on these V8 engines provide many potential points of failure.
   How to confirm: Visually inspect all vacuum hoses for cracks or disconnections. A smoke test is the most effective method to pressurize the intake system with smoke and reveal the source of any hard-to-see leaks.
   Typical fix: Replace the leaking gasket or hose. The PCV valve and its hoses are common culprits.
   Est. part cost: $10-$300 depending on the location of the leak.
5. Powertrain Control Module (PCM) Software Issue ⚪ Low Probability TSB 21-2248 and TSB 20-2336 identify that some 2020 6.7L diesel models may set P0300 and other codes due to a software glitch. TSB 18-2188 also calls for a PCM update on 2017-2018 6.2L engines for cold start misfire issues.
   How to confirm: A Ford dealership or a qualified shop with a Ford diagnostic tool (like FDRS) can check the current PCM software calibration version against the latest available version listed in the TSBs.
   Typical fix: Reprogram the PCM with the updated software. This is a simple procedure for a technician with the right tools.
   Est. part cost: $0 if under warranty, otherwise $100-$250 for labor.

Rare But Worth Checking

• Internal Engine Mechanical Failure (7.3L Lifter/Camshaft Failure): A significant known issue on early (2020-2022) 7.3L 'Godzilla' engines is the failure of valve lifters (tappets), which then damages the camshaft. This often starts as a single-cylinder misfire (like P0302 or P0304) but can present as a P0300. Symptoms include a persistent ticking noise. This is a major engine repair, often requiring engine replacement.
• Under-Torqued Crankshaft Pulley Bolt (6.8L Engine): While the 6.8L V10 was primarily for chassis-cab models, TSB SSM 46391 is a critical check for any 2017 vehicle with this engine built between Sept 2016 and Feb 2017. An under-torqued bolt can cause the crankshaft position sensor to get an erratic signal, leading to random misfires.
• Low Fuel Pressure: A weak fuel pump or clogged fuel filter can starve the engine of fuel, causing lean misfires across all cylinders. This is more likely to be noticeable under heavy load or acceleration.
• Broken Valve Spring (6.2L Engine): Though less common than on older models, the 6.2L 'Boss' V8 can suffer from broken valve springs. This typically causes a very distinct single-cylinder misfire but could initially be interpreted as a random misfire by the PCM.

Diagnosis Steps

1. Retrieve all stored trouble codes with an OBD-II scanner. Note any codes accompanying P0300 and check freeze frame data to see the conditions when the code was set.
2. If the check engine light is flashing, do not drive the vehicle to avoid catalytic converter damage.
3. Visually inspect the engine bay for obvious issues like disconnected vacuum hoses, damaged wiring, or signs of fluid leaks.
4. For 7.3L Gas Engine: Immediately suspect spark plug wires. Inspect for arcing, heat damage, or loose boots. Consider replacing all 8 as a primary diagnostic step due to the high failure rate.
5. For 6.2L Gas Engine: Inspect spark plugs (all 16) and test ignition coils by swapping them between cylinders to see if a specific misfire code appears (e.g., P0301 moves to P0302).
6. For 6.7L Diesel Engine: Diagnosis is more complex. A power balance test using a high-level scan tool is the best way to identify a misfiring cylinder, which often points to a faulty injector.
7. Check for vacuum leaks using a smoke machine. This is the most effective way to find hairline cracks in hoses or leaking intake gaskets.
8. Test fuel pressure to rule out a weak fuel pump or clogged filter.
9. If a 7.3L engine has a persistent misfire after replacing ignition components, listen carefully for valvetrain ticking and perform a compression test to check for internal mechanical engine problems like a failed lifter.

Parts You'll Likely Need

• Spark Plug Wire Set (7.3L V8) (OEM #LC3Z-12286-C) — A primary and well-documented failure point on the 7.3L 'Godzilla' engine, causing misfires.
  Trusted brands: Motorcraft, NGK, MSD
  OEM price range: $150-$250 for a set of 8
  Aftermarket price range: $70-$150
• Spark Plug (6.2L V8) (OEM #SP-526-X) — Regular maintenance item. The 6.2L engine has 16 plugs, increasing the chance of failure. Also required for the cold-start TSB fix.
  Trusted brands: Motorcraft, Autolite, Champion
  OEM price range: $8-$10 per plug
  Aftermarket price range: $5-$8 per plug
• Ignition Coil (OEM #LC3Z-12029-A (7.3L)) — A primary cause of misfires on the 6.2L and 7.3L gas engines.
  Trusted brands: Motorcraft, NGK, Denso
  OEM price range: $40-$70 per coil
  Aftermarket price range: $25-$50 per coil

Related Codes That Often Appear With This One

• P0301-P0308 — If the random misfire begins to occur more frequently on a specific cylinder, the PCM will log a cylinder-specific code alongside P0300. This is common with failing lifters on the 7.3L.
• P0171, P0174 — These 'System Too Lean' codes often accompany P0300 when the cause is a vacuum leak or insufficient fuel delivery, as the engine is getting too much air relative to fuel.
• P0603, P203B, P2201 — As noted in TSB 21-2248 and TSB 20-2336, these codes can appear with P0300 on 6.7L diesel models due to a PCM software issue that requires a reflash.
• P0316 — Misfire Detected on Startup (First 1000 Revolutions). This code is often seen with other misfire codes and is specifically mentioned in TSB 18-2188 for the 6.2L cold start issue and TSB 20-2370 for the 7.3L spark plug wire issue.

Technical Service Bulletins (TSBs) & Recalls

• TSB 21-2248
• SSM 46391
• TSB 20-2336
• TSB 20-2370
• TSB 18-2188
• TSB 25-2572
• TSB 23-2252

Platform-Specific Known Issues

• Premature Spark Plug Wire Failure: The spark plug wires, especially on early 2020 models, are known to fail due to high heat from the exhaust manifolds, causing misfires. TSB 20-2370 addresses this for some chassis, and replacing the wires with updated OEM or quality aftermarket parts is a common fix.
• Camshaft/Lifter Failure: A significant number of 2020-2022 models have experienced catastrophic failure of the valve lifters (tappets), which in turn destroys the camshaft. This often begins as a misfire code and a ticking noise. It is a major mechanical failure often requiring engine replacement.
• Cold Start Misfire/Fouling: Per TSB 18-2188, 2017-2018 models can exhibit misfires and even a crank/no-start condition in cold weather due to spark plug fuel fouling. The official fix requires a PCM software update to adjust cold-start fueling strategy.
• PCM Software Glitches: Multiple TSBs (including 21-2248 and 20-2336) have been issued for 2020 models where a software issue in the PCM can erroneously trigger a P0300 code along with a host of other DTCs. The fix is a PCM reflash at the dealership.

Mechanic-Grade Diagnostic Values

• 6.7L Power Stroke Injector Balance Rates at Idle — expected: ±4.0 mm³/stroke when engine is at operating temperature.. Failure: A consistent reading above +4.0 mm³ or below -4.0 mm³ on any cylinder points to a faulty injector or a mechanical cylinder issue. A positive number means the PCM is adding fuel to compensate for a weak cylinder, while a negative number means it's removing fuel from an over-fueling injector.
• Gas Engine Fuel Pressure at Idle — expected: 35-60 PSI. Failure: Pressure consistently below 35 PSI suggests a weak fuel pump or a clogged fuel filter.
• Mode $06 Misfire Count — expected: Near zero counts per cylinder over the last 10 drive cycles.. Failure: A high number of misfire counts on one or more cylinders, even without a specific P030x code, indicates an intermittent issue that needs investigation. The threshold to set a code can be as low as a 2% misfire rate.
• Ignition Coil Secondary Resistance (Gas Engines) — expected: Approximately 8-12 kΩ (kilo-ohms).. Failure: A reading significantly outside this range indicates a faulty ignition coil.

Hidden / Shadow Codes Worth Checking

• Mode $06, Test ID $A2-$AB: This is not a traditional DTC but a diagnostic monitor within the PCM. It stores the raw misfire counts for each cylinder (e.g., Test ID $A2 for Cylinder 1, $A3 for Cylinder 2, etc.) for the last 10 driving cycles. These counts can reveal a cylinder that is starting to fail before the misfire rate is high enough to trigger a P0300 or a cylinder-specific code. (see via A capable OBD-II scanner with Mode $06 functionality, such as FORScan or a professional-grade tool.)

Scan Tool Commands That Help

• Ford IDS, FORScan, Snap-on, etc.: Power Balance Test — This is a primary diagnostic step for P0300 on both gas and diesel engines. It graphically displays the RPM contribution of each cylinder in real-time. A cylinder with a significant dip is misfiring. The function also allows the user to manually disable individual injectors to confirm the misfiring cylinder and see if the engine note changes.
• Ford IDS/FDRS, FORScan, high-end scanners: Misfire Monitor Neutral Profile Correction — This procedure MUST be performed after replacing the PCM, crankshaft position sensor, crankshaft pulley, or performing major internal engine or transmission repairs. It relearns the profile of the crankshaft teeth to accurately detect misfires. Failing to perform this can cause the PCM to log false P0300 codes.
• Ford IDS, FORScan, etc.: Relative Compression Test — As a quick, non-invasive way to check for a base engine mechanical problem. If a misfire is suspected to be from low compression, this test can identify a weak cylinder by measuring cranking speed variations, saving the time of a traditional compression test.

Real Owner Repair Stories

• YouTube user, '2020 F250 Super Duty 7.3 Godzilla misfire SOLVED.' (2020 Ford F-250 7.3L 'Godzilla' V8) — Popping under hard acceleration, flashing check engine light, rough idle, P0300 code and a non-stored code for cylinder 2 misfire.
  ❌ Tried (didn't work) Initial diagnosis pointed towards spark plug wires.
  ✅ What actually fixed it The owner replaced all 8 original spark plug wires with an aftermarket set (Ultima Selects from O'Reilly's) for $74. This completely resolved the misfire, improved shifting, and smoothed the idle. The dealership quoted $38 per wire.
• Ford Truck Enthusiasts Forum user 'b-uno' (2017 Ford F-250 6.2L V8 with 64,000 miles) — Intermittent P0300 code, similar to another user with 75,000 miles.
  ❌ Tried (didn't work) The user was asking for advice before trying fixes.
  ✅ What actually fixed it The user reported that replacing the spark plugs and wires resolved the P0300 code.
• The Fast Lane Truck (TFLtruck) (2020 Ford F-250 Super Duty 7.3L V8) — Engine misfire, rendered the truck undrivable.
  ❌ Tried (didn't work) Waiting for parts, as the specific wire was on backorder due to high failure rates.
  ✅ What actually fixed it The cause was identified as a faulty spark plug wire. The fix required replacing the wire with a newly redesigned part from Ford, which addressed the quality issue causing the failures.

OEM Part Supersession History

• LC3Z-12286-A, LC3Z-12286-B → LC3Z-12286-C, and later LC3Z-12286-D (Motorcraft WR-6170 is a related kit number) — The original spark plug wires for the 7.3L 'Godzilla' V8 were highly prone to heat damage from the exhaust manifolds, causing the boots to degrade and the spark to arc to ground. The revised parts have improved heat shielding and more durable materials.
  Heads up: Using the original or early-revision part numbers will likely lead to a repeat failure. It is critical to install revision 'C' or newer for a durable repair. TSB 20-2370 officially documents this change.

Model Year Variations Within This Range

• 2017-2018: F-Super Duty models with the 6.2L V8 built on or before May 2, 2018, may have a PCM calibration that causes spark plug fuel fouling and misfires during cold starts. TSB 18-2188 provides a software update to correct this.
• 2020: The 7.3L V8 was introduced. Early production models are highly susceptible to spark plug wire failure due to heat. Ford acknowledged the issue and released updated parts (LC3Z-12286-C and later).
• 2020-2021: Models with the 6.7L Power Stroke diesel may exhibit P0300 due to a PCM software glitch, as outlined in TSB 21-2248 and TSB 20-2336. The fix is a PCM reflash, not a component replacement.