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

Direct-injection high-pressure fuel pump / injector failures

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

Symptoms

hard starts, long crank, fuel-pressure codes; rough running under load
owner-reported high-pressure fuel pump replacements at dealer rates (GM-Trucks HD forum)

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

The L8T is direct-injected (Gen V small-block architecture) and carries a cam-driven high-pressure pump; HD-forum owners report HPFP failures, and DI injectors are the standing wear/contamination surface of the architecture. No authoritative failure statistics or a documented defect pattern exist for the L8T specifically in the open record.

Diagnosis

log requested vs actual rail pressure on a suspected HPFP fault; rule out the low-pressure side first
check injector balance/contribution before replacing hardware; verify fuel quality

Fixes

replace the failed HPFP or injector(s); keep the fuel system clean - DI pumps are unforgiving of contamination ()

Prevalence

occasional