Rough Idle & Misfire on 2020 Ram 1500 Hemi - Spark Plugs?

A P0304 code (Misfire Detected - Cylinder 4) combined with a rough idle and hesitation at 65,000 miles on your 2020 Ram 1500 Hemi strongly suggests that worn spark plugs are a primary suspect. The 5.7L Hemi engine does indeed use 16 spark plugs (two per cylinder), and they are a critical maintenance item.

Here's what you should know and do:

1. Spark Plug Replacement Interval: For the 5.7L Hemi, the recommended spark plug replacement interval is typically every 30,000 miles for copper plugs or 100,000 miles for iridium/platinum plugs, depending on the factory-installed type. At 65,000 miles, if your truck still has its original copper plugs, they are well past due and definitely a cause for misfires. Even if they are longer-life plugs, they could be contributing.
2. Recommended Plugs: Stick with OEM-equivalent plugs. Many Hemi owners have good success with NGK or Champion copper plugs (e.g., NGK 5306 or Champion RE14MCC4). Ensure you get the correct heat range and gap them properly if they don't come pre-gapped for your specific application.
3. Coil Packs: While replacing the plugs, inspect the coil pack for cylinder 4 (and others) for any signs of damage or corrosion. A failing coil pack can also cause a misfire. If the misfire persists after new plugs, the coil pack would be the next item to check.
4. Fuel Injector: Less common, but a clogged or faulty fuel injector for cylinder 4 could also cause a misfire. This is usually diagnosed after ruling out plugs and coils.

When to See a Shop: If replacing all 16 spark plugs and checking the coil pack for cylinder 4 doesn't resolve the P0304 code and rough idle, or if you're uncomfortable performing the plug change yourself (it can be time-consuming due to the number of plugs and access), it's best to take your truck to a qualified mechanic. They can perform further diagnostics, such as compression tests, fuel pressure tests, and injector flow tests, to pinpoint more complex issues.