Rough Idle & Misfires on 2018 Ram 1500 5.7L Hemi - Spark Plug Time?

ClearTheCode admin answer:

Yes, at 85,000 miles, it is highly probable that worn spark plugs are the primary cause of your rough idle and misfire codes (P0301, P0303) on your 2018 Ram 1500 5.7L Hemi. The Hemi engine's design with two spark plugs per cylinder means there are 16 plugs in total, and they are critical for efficient combustion.

Here's a breakdown:

1. Spark Plug Interval: Chrysler/Ram generally recommends replacing the spark plugs on the 5.7L Hemi every 30,000 miles. At 85,000 miles, if they haven't been changed since 40,000 miles, they are well past their service life. Worn electrodes and increased gaps will lead to weak spark, misfires, and reduced fuel efficiency.
2. Misfire Codes (P030x): Codes like P0301 and P0303 specifically indicate a misfire on cylinder 1 and 3, respectively. While worn plugs are the most common cause, other factors can contribute:
   • Ignition Coils: A failing ignition coil pack for a specific cylinder can also cause misfires. You can swap the coil packs from a misfiring cylinder to a non-misfiring one to see if the code follows the coil.
   • Fuel Injectors: A clogged or faulty fuel injector can lead to an improper air/fuel mixture, causing a misfire. This is less common than plugs/coils but possible.
   • Compression Issues: In rare cases, low compression in a cylinder can cause misfires.

DIY Steps:

• Replace Spark Plugs: This is a highly recommended DIY job. You'll need 16 new spark plugs (OEM recommended are usually NGK or Champion Iridium), a spark plug socket, extensions, and a torque wrench. Ensure you gap them correctly if they aren't pre-gapped. Take care when removing and installing to avoid cross-threading.
• Inspect Coil Packs: While you have the coil packs off to access the plugs, visually inspect them for any cracks or signs of damage.

When to see a shop:

• If replacing the spark plugs does not resolve the misfire codes, or if the codes reappear after clearing them.
• If you suspect a faulty coil pack and don't want to troubleshoot it yourself.
• If you suspect a fuel injector issue or a more serious internal engine problem like low compression, as these require specialized diagnostic tools and expertise.