Recipe - 6.6L V8 Gasoline (GM HD, L8T 2020+)
Reliability build
Reliability tier: aggregated - verify before ordering, see /disclosure/
L8T ignition service (mode Ignition service wear: spark plugs and coils): no L8T-specific defect exists - this is conventional Gen V truck hardware on service intervals, and the honest recipe is interval discipline. Plugs (12622441) and wires on schedule keep the big V8 smooth under HD towing; misfires under load on a young engine are usually this before anything exotic.
Parts
- 6.6L L8T Spark Plug (OEM) - OEM plugs (12622441) - renew as a full set on interval (qty 8)
- 6.6L L8T Spark Plug Wire (OEM) - individual wire replacement where a leg tests bad (12716289) (qty 1)
- 6.6L L8T Spark Plug Wire Kit (OEM) - full wire set (12737722) at higher mileage (qty 1)
Install order
- misfire diagnosis first (which cylinder, load-dependent or not)
- renew plugs as a set - a 16-plug-concept V8 runs worst on mixed plug ages
- wires: individual legs where bad, full set at higher mileage
Expected outcome
Smooth HD towing, no load misfires.
Do not
- do not chase injectors or HPFP before a clean misfire diagnosis - DI misfires still start at the spark
Parts budget
About $20-$120 in parts. It depends on what the diagnosis finds; each option below is what you buy together. Prices marked "at Dave's" are Dave's Auto Center's, the same as in his store; the others are approximate prices from OEM and maker catalogs, rounded (a manufacturer's list price can run higher). Parts only, no labor.
DIY or shop: DIY: conventional access, hand tools.