P0308 on 2019-2023 Ram 1500 5.7L HEMI: Cylinder 8 Misfire Causes and Fixes

What's Unique About the 2019-2023 Ram 1500

On the 5th generation Ram 1500 with the 5.7L HEMI, a P0308 code isn't just a simple tune-up issue. While spark plugs and coils are common culprits, this engine family has a well-documented history of camshaft and lifter failures, which can cause a persistent misfire on a single cylinder. This failure is often preceded by an audible ticking noise, commonly called the 'Hemi tick'. Additionally, Ram has issued a Technical Service Bulletin (TSB #18-006-24) that addresses this and other misfire codes with a simple software update to the PCM, which should not be overlooked.

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 shaky idle
• Engine hesitation or stumbling during acceleration
• Noticeable loss of power
• Solid or flashing Check Engine Light
• Audible ticking or tapping noise from the engine, especially if the cause is mechanical
• Exhaust noise on startup

Most Likely Causes

1. Worn Spark Plugs or Faulty Ignition Coil 🔴 High Probability The 5.7L HEMI uses two spark plugs per cylinder, increasing the chance of a failure. Ignition coils are a common wear item on most modern engines and a primary suspect for a single-cylinder misfire.
   How to confirm: Swap the ignition coil from cylinder 8 with another cylinder (e.g., cylinder 6 on the same passenger-side bank). Clear the codes and drive. If the code changes to P0306, the coil is bad. If not, swap the two spark plugs from cylinder 8 with another cylinder. If the code then moves, a spark plug was the issue.
   Typical fix: Replace the faulty ignition coil or all 16 spark plugs. It's recommended to replace all spark plugs at once for even performance.
   Est. part cost: $30-$70 for an ignition coil, $50-$150 for a set of 16 spark plugs.
2. Failed Camshaft Lobe and/or Lifter 🟡 Medium Probability The 5.7L HEMI engine, particularly with the Multi-Displacement System (MDS), is known for a valvetrain issue often called the "Hemi tick." A hydraulic lifter, often one of the MDS lifters, can fail, causing the roller to stop spinning and grind down the corresponding lobe on the camshaft. This prevents the valve from opening correctly, leading to a persistent misfire that won't be resolved by new plugs or coils.
   How to confirm: This is a more advanced diagnosis. It often starts with an audible ticking sound. A mechanic can perform a compression test; a cylinder with a wiped cam lobe will often show lower compression. The definitive check is to remove the passenger-side valve cover to visually inspect the rocker arms and valve springs for cylinder 8. A dislodged rocker arm is a clear sign of a collapsed lifter.
   Typical fix: This is a major repair requiring the replacement of the camshaft, all lifters, and associated gaskets and seals. It is often recommended to disable the MDS system with a non-MDS camshaft and lifters 🎬 See a professional mechanic perform a 5.7L HEMI camshaft replacement. to prevent recurrence.
   Est. part cost: $800-$1500 for a camshaft and lifter kit.
3. Outdated PCM Software 🟡 Medium Probability Manufacturer TSB #18-006-24 explicitly lists P0308 and other misfire codes as being potentially resolved by a PCM software update. The logic for detecting misfires may be too sensitive in older software versions, leading to false positives.
   How to confirm: A Ram dealership or a qualified shop with access to OEM software tools can check the current software version on your PCM and see if an update is available based on your VIN and the TSB.
   Typical fix: Reprogramming the Powertrain Control Module (PCM) with the latest software.
   Est. part cost: $0-$200, depending on dealer labor rates.
4. Faulty Fuel Injector ⚪ Low Probability
   How to confirm: After ruling out the spark plug and coil, you can swap the fuel injector from cylinder 8 with another cylinder. If the misfire code follows the injector, the injector is faulty.
   Typical fix: Replace the faulty fuel injector.
   Est. part cost: $50-$120 for a single injector.

Rare But Worth Checking

• Intake Manifold Gasket Leak: A vacuum leak near the intake runner for cylinder 8 can lean out the air/fuel mixture and cause a misfire on just that cylinder. This can be diagnosed with a smoke test.
• Damaged Wiring Harness: Rodents can chew wires, or a wire can chafe and break, interrupting the signal to the ignition coil or fuel injector for cylinder 8. A visual inspection of the harness leading to cylinder 8 is necessary.
• Low Engine Compression: Beyond a cam/lifter issue, a problem with piston rings or cylinder head valves can cause low compression and a misfire. A compression test is needed to confirm.
• Oil Contamination in Spark Plug Tube: A leaking valve cover gasket or spark plug tube seal can allow oil to fill the tube for cylinder 8, shorting out the spark plug and ignition coil, causing a misfire.
• Broken Exhaust Manifold Bolt / Leak: The HEMI engines are known for exhaust manifold bolts breaking, especially on the rear cylinders like #8. This can cause a ticking noise (often mistaken for the 'Hemi tick') and can allow outside air to be drawn into the exhaust stream, confusing the O2 sensor and potentially leading to a misfire code on that bank.
🎬 Watch how to fix a cracked manifold and broken exhaust bolts.

Diagnosis Steps

1. Scan for any other accompanying trouble codes.
2. Check with a dealer if your vehicle's VIN is covered by TSB #18-006-24 for a PCM software update.
3. Locate cylinder 8 (passenger side, rearmost cylinder).
4. Swap the ignition coil from cylinder 8 with another cylinder (e.g., cylinder 6). Clear codes and see if the misfire moves to P0306.
5. If the misfire remains on cylinder 8, inspect the spark plug tube for oil contamination. Then, swap the two spark plugs from cylinder 8 with those from another cylinder. See if the misfire moves.
6. Inspect the wiring and connector for the cylinder 8 ignition coil and fuel injector for any visible damage, chafing, or signs of rodents.
7. If the misfire still persists, swap the fuel injector from cylinder 8 with another cylinder and see if the code follows.
8. Listen for a distinct ticking noise from the engine, which could indicate a lifter/camshaft issue or a broken exhaust manifold bolt.
9. Perform an engine compression test on cylinder 8 and compare it to a known good cylinder. A significant difference may point to a mechanical problem like a worn cam lobe, bad rings, or valve issues.

Parts You'll Likely Need

• Ignition Coil (OEM #68238603AA) — This is one of the most common failure points for a single-cylinder misfire.
  Trusted brands: Mopar, NGK, Delphi
  OEM price range: $40-$100
  Aftermarket price range: $20-$50
• Spark Plugs (OEM #SPLZFR5C11) — Spark plugs are a regular maintenance item and a primary cause of misfires. The HEMI engine uses two per cylinder.
  Trusted brands: Mopar, NGK, Champion
  OEM price range: $100-$180 (set of 16)
  Aftermarket price range: $50-$120 (set of 16)
• Fuel Injector (OEM #68361162AB) — A clogged or failed injector will prevent fuel from reaching cylinder 8, causing a misfire.
  Trusted brands: Mopar, Bosch, Standard Motor Products
  OEM price range: $60-$90
  Aftermarket price range: $40-$70
• Camshaft and Lifter Kit — Fixes the common and severe 'Hemi tick' issue where a failed lifter damages the camshaft, causing a permanent misfire. Kits often include non-MDS lifters for improved durability.
  Trusted brands: Mopar, Melling, COMP Cams, Texas Speed (TSP), Brian Tooley Racing (BTR)
  OEM price range: $1000-$1800
  Aftermarket price range: $700-$1500

Related Codes That Often Appear With This One

• P0300 — If the condition causing the misfire on cylinder 8 is also intermittently affecting other cylinders (e.g., due to a widespread fuel delivery or vacuum issue), a P0300 (Random/Multiple Cylinder Misfire) code may also be present.

Technical Service Bulletins (TSBs) & Recalls

• 18-006-24: Addresses engine misfire codes P0300-P0308 and recommends reprogramming the PCM.
• 18-145-22: Lists P0308 as a potential diagnostic trouble code related to electrical system issues.

Platform-Specific Known Issues

• TSB #18-006-24: PCM Software Update: A bulletin issued by Ram states that a P0308 code (among other misfires) may be resolved by reprogramming the PCM with updated software to correct overly sensitive misfire detection logic.
• Camshaft/Lifter Failure ('Hemi Tick'): The 5.7L HEMI is known for developing a ticking noise that is often a precursor to a failed MDS lifter and a damaged camshaft lobe. This is a major mechanical failure that can cause a persistent P0308 code that is not fixed by replacing ignition or fuel components.

Mechanic-Grade Diagnostic Values

• Fuel Pressure (at fuel rail) — expected: 58 +/- 5 PSI. Failure: Pressure significantly below 53 PSI or that drops under load can indicate a weak fuel pump.
• Fuel Injector Resistance — expected: Approximately 11-12 ohms. Failure: A reading significantly higher or lower (e.g., open circuit or near zero) indicates a failed injector coil.

Scan Tool Commands That Help

• wiTECH (OEM FCA Tool): Cylinder Misfire Test — This function allows a technician to actively monitor misfire counts per cylinder in real-time, helping to confirm if the misfire is constant or intermittent and under what specific operating conditions it occurs.
• wiTECH (OEM FCA Tool): Fuel Injector Kill — This bidirectional command allows the user to disable the fuel injector for cylinder 8. If disabling the injector causes no change in engine idle quality, it confirms that cylinder 8 was not contributing, pointing towards a problem with that cylinder's fuel, spark, or compression.

Wiring & Ground Locations

• G908 — Right rear of engine compartment.. This is a primary ground point for multiple engine components. A loose or corroded connection here could potentially cause erratic behavior or failure of ignition or fuel system components on the right bank of the engine, where cylinder 8 is located.
• Cylinder 8 Ignition Coil Connector — Passenger side of the engine, rearmost coil.. The wiring to this connector can be susceptible to heat damage from the exhaust manifold or rodent damage. A visual inspection for chafed, melted, or chewed wires is a critical step if swapping the coil doesn't resolve the misfire.
• Cylinder 8 Fuel Injector Connector — Under the intake manifold, passenger side, rearmost injector.. Similar to the coil connector, the wiring harness leading to the injector can be damaged. Testing for voltage and ground at this connector is necessary if an injector swap points to a circuit issue rather than a component failure.

Real Owner Repair Stories

• YouTube channel 'smoran2006' (2006 Ram 1500 5.7L (Note: Older model but demonstrates identical failure mode common to the HEMI engine family)) — Check engine light with code P0308, engine tick.
  ❌ Tried (didn't work) Replacing the spark plug for cylinder 8., Swapping ignition coils between cylinders.
  ✅ What actually fixed it Upon removing the valve cover, the owner found the rocker arm for one of the valves on cylinder 8 had completely fallen off and was lying in the head. This was caused by a collapsed hydraulic lifter, which prevented the valve from opening and resulted in the misfire. The fix was to replace the failed lifter and reinstall the rocker arm.

When the Usual Fixes Don't Work

• In one documented case for a similar HEMI engine, after replacing plugs, coils, and injectors for a P0308, the owner discovered the root cause was a failed hydraulic lifter which caused a rocker arm to become dislodged. This meant the valve for that cylinder was not opening at all, causing a complete lack of combustion that no ignition or fuel part could fix. This highlights that on a HEMI, persistent single-cylinder misfires, especially when accompanied by a ticking noise, warrant a mechanical inspection of the valvetrain sooner rather than later.

OEM Part Supersession History

• 56029129AA, 56029129AB, 56029129AF, 68060346AA → 68238603AA — Standard part evolution for improved reliability or manufacturing changes.

Model Year Variations Within This Range

• 2019+: The 5.7L HEMI in the 5th generation Ram 1500 was available with or without the eTorque mild-hybrid system. While the base engine and ignition system are largely the same, the eTorque system adds a 48-volt motor-generator. While not a direct cause of a P0308, diagnosing electrical issues on an eTorque model requires consideration of this additional high-voltage system.