Failure mode - GM 6.0L V8 Gasoline (GM HD, LY6-L96 2008-2019; Express/Savana vans 2008-2020)

Ignition misfire: coils and spark plugs (L96/LY6)

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

Symptoms

rough idle and flashing MIL on a cold start; cylinder-specific misfire codes
coil-on-plug failures (one per cylinder, 16 plugs on the V8); worn plugs at 100k service intervals

Compare with the other causes of the same sign on this engine: misfire, rough idle, hesitation or surging (3 causes)

Root cause

Coil-on-plug packs fail with heat cycles and plugs wear at the 100k service interval; a weak coil or a wide-gap plug drops one cylinder, flashing the MIL. On a 16-plug V8 the plug-side is the first suspect, the coil-side the cheap swap-test.

Diagnosis

read the specific cylinder misfire counters, then swap the coil to another cylinder to separate coil from plug
check plug gaps and boots on the failed cylinder before replacing the coil

Fixes

renew failed coils and/or plugs (full-set plug service at the interval) ()

spark-plug - more than one option: GM 6.0L HD Spark Plug 2008-2014 (OEM), GM 6.0L HD Spark Plug 2015-2019 (OEM)
GM 6.0L HD Ignition Coil (OEM)

Prevalence

common

Parts for this repair run about $85-$240: see them next to the other repairs on this engine in repair costs.