P0308 on 2014-2015 Ram 3500: Cylinder 8 Misfire Causes and Fixes

What's Unique About the 2014-2015 Ram 3500

On the 2014-2015 Ram 3500, this code only applies to the 5.7L or 6.4L Hemi V8 engines, as the Cummins diesel is an inline-6. While ignition components are the usual suspects, these Hemi engines are known for a specific mechanical issue often called the 'Hemi Tick.' This can refer to two distinct issues: a relatively minor exhaust manifold leak from broken studs, or a much more serious failure of the hydraulic lifters (particularly the Multi-Displacement System (MDS) lifters on the 5.7L). A failed lifter's roller bearing can seize, destroying the camshaft lobe for that cylinder and causing a persistent misfire that a simple tune-up won't fix.

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
• Hesitation or stumbling during acceleration
• Noticeable loss of engine power
• Flashing or solid Check Engine Light
• Smell of unburnt fuel from the exhaust
• Audible ticking noise from the engine bay, which may be louder on startup and quiet down as the engine warms

Most Likely Causes

1. Worn or Fouled Spark Plug(s) 🔴 High Probability → Shop Spark Plug Hemi engines use two spark plugs per cylinder (16 total), increasing the chances of a single plug failing. They are a regular maintenance item, typically recommended for replacement around 100,000 miles.
   How to confirm: Remove the two spark plugs from cylinder #8 (passenger side, rear-most). Inspect for wear, oil fouling, or damage. Compare them to plugs from a known good cylinder. The factory gap is typically 0.043 inches (1.1mm).
   Typical fix: Replace all 16 spark plugs as a set. It is not recommended to replace only the plugs for cylinder 8.
   Est. part cost: $80-$150
2. Failed Ignition Coil 🔴 High Probability → Shop Ignition Coil
   How to confirm: Swap the ignition coil from cylinder #8 with an easily accessible coil, for example, cylinder #2 (passenger side, front-most). Clear the codes and drive the vehicle. If the code changes to P0302, the coil is faulty. 🎬 See this video for an easy Hemi misfire diagnosis walkthrough.
   Typical fix: Replace the failed ignition coil. Many technicians recommend replacing the spark plugs at the same time.
   Est. part cost: $40-$90
3. Failed Camshaft Lobe and/or Lifter 🟡 Medium Probability → Shop Engine Camshaft The Hemi engines of this era are known for lifter failures, often preceded by a distinct ticking sound. The roller on the lifter can seize, causing it to grind down the camshaft lobe. This is especially common with the MDS lifters on the 5.7L engine. This prevents the valve from opening fully, causing a permanent misfire. 🎬 Watch: See what a failed Hemi lifter and camshaft look like.
   How to confirm: After ruling out ignition and fuel issues, listen for a loud, rhythmic ticking from the engine, especially on a cold start. A mechanic will remove the valve cover to visually inspect the valvetrain for cylinder #8, looking for a dislodged rocker arm or limited movement. A compression test showing low or zero compression on cylinder #8 is a strong indicator.
   Typical fix: This is a major repair requiring replacement of the camshaft, all 16 lifters, head gaskets, and associated components. Many owners and shops opt to replace the MDS lifters with superior non-MDS 'Hellcat' lifters (Mopar Part #5038784AD) to prevent recurrence, which requires turning off MDS in the PCM.
   Est. part cost: $800-$2000
4. Clogged or Faulty Fuel Injector ⚪ Low Probability → Shop Fuel Injector
   How to confirm: After ruling out ignition problems, swap the fuel injector from cylinder #8 with another cylinder. If the misfire code follows the injector, the injector is bad. This is more labor-intensive than an ignition coil swap.
   Typical fix: Replace the faulty fuel injector.
   Est. part cost: $50-$120

Rare But Worth Checking

• Intake Manifold Gasket Leak: → Shop Engine Intake Manifold A vacuum leak near the intake runner for cylinder #8 can lean out the air/fuel mixture enough to cause a misfire on just that cylinder.
• Low Compression (Valves, Piston Rings): If not caused by a lifter/cam failure, a burnt exhaust valve or damaged piston rings can cause low compression and a persistent P0308. A compression test is required to diagnose this.
• Wiring Harness Issue: In some cases, rodents have been known to chew through the injector or coil wiring for a single cylinder, causing an intermittent or constant misfire. A visual inspection of the harness leading to cylinder #8 is warranted if other tests fail.

Diagnosis Steps

1. Confirm the P0308 code with an OBD-II scanner. Note if the check engine light is steady or flashing and check for any other codes like P0300 or P2323.
2. Listen carefully to the engine, especially on a cold start. Note any loud, rhythmic ticking noises and their location. A stethoscope can help isolate the sound to the valve cover (potential lifter) or exhaust manifold (potential leak).
3. Identify cylinder #8, which is the rearmost cylinder on the passenger side of the engine.
4. Swap the ignition coil from cylinder #8 with the coil from cylinder #2 (front, passenger side). Clear the codes and test drive. If the code changes to P0302, the coil is bad and needs replacement.
5. If the code remains P0308, inspect the two spark plugs for cylinder #8. If they are worn, fouled, or damaged, replace all 16 spark plugs.
6. If ignition components are good, visually inspect the wiring harness leading to the coil and injector for cylinder #8 for any signs of damage, such as from rodents.
7. If the misfire persists, the next step is to check the fuel injector. This can be done by swapping it with another cylinder's injector to see if the misfire follows, though this is more labor-intensive.
8. If a mechanical tick is present and all other steps have failed, perform a compression test on cylinder #8. A significant loss of compression strongly suggests an internal mechanical problem like a failed lifter/camshaft.
9. As a final confirmation for lifter failure, a mechanic will remove the passenger-side valve cover to observe the rocker arms on cylinder #8 while the engine is manually turned. Lack of movement or a dislodged rocker arm confirms the diagnosis.

Parts You'll Likely Need

• Ignition Coil (OEM #68238603AA) — Ignition coils are a common failure item due to high heat and vibration in the engine bay, leading directly to a misfire on a single cylinder.
  Trusted brands: Mopar, NGK, Delphi
  OEM price range: $60-$90
  Aftermarket price range: $40-$70
• Spark Plugs (OEM #SP138239AC (for 6.4L), SPLZFR5C11 (for 5.7L)) — As a standard maintenance item, worn spark plugs are a primary cause of weak spark and incomplete combustion, resulting in a misfire.
  Trusted brands: Mopar, NGK, Champion
  OEM price range: $100-$150 (set of 16)
  Aftermarket price range: $80-$120 (set of 16)
• Camshaft and Lifter Kit (OEM #Multiple, but non-MDS upgrade is popular: Lifters are Mopar 5038784AD) — For the well-known 'Hemi Tick' issue, a failed lifter damages the camshaft, requiring both to be replaced to resolve the resulting mechanical misfire. Upgrading to non-MDS lifters is a common preventative measure.
  Trusted brands: Mopar, Melling, Comp Cams
  OEM price range: $1000-$1500
  Aftermarket price range: $700-$1200

Related Codes That Often Appear With This One

• P0300 — If the misfire becomes more frequent or other cylinders begin to misfire (which can happen as a failing camshaft sheds metal particles through the engine), a P0300 (Random/Multiple Misfire) code may appear alongside P0308.
• P0430 — This code (Catalyst System Efficiency Below Threshold Bank 2) can be triggered by a persistent P0308 misfire. Unburnt fuel from cylinder 8 damages the catalytic converter on Bank 2 (the passenger side).
• P2323 — This code for 'Ignition Coil H Secondary Circuit' can appear with P0308, pointing more specifically to a failure in the ignition coil or its related wiring for cylinder 8.

Technical Service Bulletins (TSBs) & Recalls

• 1810722REVA
• 18-062-16
• 18-055-15

Platform-Specific Known Issues

• The 5.7L and 6.4L Hemi engines are known for camshaft/lifter failure, often presenting as a single-cylinder misfire accompanied by a loud ticking noise. This is a significant mechanical repair. On the 5.7L, this is often attributed to the failure of the MDS (Multi-Displacement System) lifters. Many owners who perform the repair choose to install non-MDS lifters from the 6.4L or 'Hellcat' engines for improved durability.

Mechanic-Grade Diagnostic Values

• Ignition Coil Primary Resistance — expected: 0.558 - 0.682 Ohms at 70-80°F. Failure: A reading outside of this range indicates a faulty coil.
• Fuel Injector Resistance (5.7L/6.4L Hemi) — expected: 11-16 Ohms. Failure: A reading of infinity (Open Loop) or significantly outside this range indicates a failed injector.
• Fuel Pressure (Cranking/Key On) — expected: 58 PSI (± 2 PSI). Failure: Pressure significantly below this specification indicates a fuel delivery problem (e.g., weak pump, clogged filter) that could cause misfires, though it would typically affect multiple cylinders.

Hidden / Shadow Codes Worth Checking

• Mode $06, Test ID $0C, Component ID $08: Accessing Mode $06 data with a professional scan tool can show raw misfire counts for each cylinder, including cylinder 8 (Component ID $08). This allows a technician to see if cylinder 8 has a higher misfire count relative to other cylinders, even if the count is not yet high enough to trigger the P0308 code. (see via A professional-grade scan tool with Mode $06 capability is required. The data is presented in hexadecimal and may need to be translated by the scan tool software.)

Scan Tool Commands That Help

• wiTECH (or equivalent professional scanner): Cylinder Contribution Test — This bidirectional test allows the technician to sequentially disable each fuel injector while monitoring the engine's RPM drop. If disabling cylinder #8 results in little or no change in RPM compared to other cylinders, it confirms that cylinder #8 is not contributing power, isolating the fault.
• wiTECH (or equivalent professional scanner): Fuel Injector Kill — Similar to a cylinder contribution test, this function specifically deactivates a single injector (e.g., cylinder 8) to confirm if it is the source of the misfire. This helps differentiate between a fuel and spark issue without swapping parts.

Wiring & Ground Locations

• Cylinder 8 Coil and Injector Harness — The wiring for cylinder 8 runs along the passenger side of the engine, near the firewall. It is part of the main engine harness.. This area is susceptible to heat damage from the exhaust manifold and physical damage from rodents. A visual inspection for melted, brittle, or chewed wires is crucial if ignition and fuel component swaps do not resolve the issue.
• Ignition Coil Capacitor — Located in the right-rear section of the engine compartment, often mounted near the firewall.. This capacitor dampens electrical noise on the 12V supply wire to the ignition coils. While a failure is rare, it could potentially cause erratic coil performance and contribute to misfires.
• PCM Ground — Key engine and PCM grounds are typically located on the engine block, near the alternator, and on the chassis frame near the battery.. A poor ground connection for the PCM or the ignition system can cause a weak or inconsistent spark, leading to misfire codes. Checking that main ground straps are clean and tight is a valid diagnostic step for persistent electronic issues.

Real Owner Repair Stories

• YouTube user 'Ram 1500 P0308 and Tick - Found The Problem' (Ram 1500 (year not specified, but Gen 4 Hemi) with 245,000 miles) — P0308 code, audible ticking noise.
  ❌ Tried (didn't work) Replacing the spark plug on cylinder 8., Swapping ignition coils between cylinders.
  ✅ What actually fixed it Upon removing the valve cover, the owner discovered the rocker arm for cylinder 8 had completely fallen off because the lifter underneath it had failed. The fix was to replace the failed lifter and reinstall the rocker arm.
• YouTube user 'Auto Repair Champs' (2014 Dodge Ram 2500 HD 5.7L Hemi) — P0300 (Random Misfire) and P0308 (Cylinder 8 Misfire).
  ❌ Tried (didn't work) Initial diagnosis pointed towards common issues like spark plugs or valve springs.
  ✅ What actually fixed it After removing the valve cover, the technician found that the valve springs were intact, but the pushrods for cylinder 8 were bent and showed signs of rubbing. Replacing the bent intake and exhaust pushrods for cylinder 8 resolved the misfire codes.
• RamForum.com user 'fire101fighter' (2010 Ram 5.7 Hemi (similar engine architecture)) — Persistent P0308 code.
  ❌ Tried (didn't work) Replacing all spark plugs., Swapping the ignition coil from cylinder 8 to cylinder 4., Replacing a warped exhaust manifold with snapped studs on the passenger side.
  ✅ What actually fixed it The user's issue remained unresolved in the thread after trying the common ignition and exhaust fixes, leading other members to suggest the next steps were to investigate the fuel injector or a potential mechanical valve/lifter issue, requiring a compression test or valve cover removal.

OEM Part Supersession History

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

Model Year Variations Within This Range

• 2014-2015: For the 2014 model year, the 6.4L Hemi V8 was introduced as a new standard engine option for the Ram 3500, re-tuned from its SRT counterpart for better low-end torque suitable for towing. There are no significant documented differences in the common causes or diagnostic procedures for P0308 between the 2014 and 2015 model years for either the 5.7L or 6.4L engines.