6.4L HEMI V8
6.4L HEMI misfire diagnosis
Misfire diagnosis on the 6.4L HEMI.
Why this matters on the 6.4L HEMI V8
Dual-plug ignition and valvetrain wear are common causes.
Symptoms owners notice
- Misfire
- Rough idle
What we check
- Coil and plug tests
- Compression
Related causes we rule out
- Worn spark plugs or a failing coil — the 6.4L HEMI fires two plugs per cylinder (16 total), so one weak plug can still set a misfire
- A failed MDS lifter on a deactivating cylinder (1, 4, 6 or 7), which shows up as a misfire concentrated on those cylinders
- A sticking or leaking fuel injector
- Vacuum leaks at the intake manifold or PCV system
Repair work involved
- Ignition or valvetrain repairs
Repair considerations
- Plugs are normally replaced as a full set of 16 rather than one at a time
- If misfire counts point to MDS cylinders, the valvetrain is inspected before ignition parts are replaced
- A misfire with a tick or metal in the oil changes the job from a tune-up to lifter/cam work