Failure mode - 6.6L V8 Gasoline (GM HD, L8T 2020+)

Ignition service wear: spark plugs and coils

Reliability tier: aggregated - verify before ordering, see /disclosure/

Symptoms

misfire codes, rough idle, hard starts as plugs/coils reach service life (routine wear, not a defect pattern)

Compare with the other causes of the same sign on this engine: hard start, long crank or no-start (2 causes) · misfire, rough idle, hesitation or surging (4 causes)

Root cause

Conventional Gen V truck ignition hardware wearing at service intervals. No L8T-specific ignition defect (compare the Triton 2V/3V spark-plug failures - a different, older architecture) is documented in the open record.

Diagnosis

coil-swap or plug-well inspection to localize a misfire before ordering coils

Fixes

replace spark plugs at the service interval; replace the failed coil(s) localized by swap test ()

Prevalence

occasional

Parts for this repair run about $20-$120: see them next to the other repairs on this engine in repair costs.