Failure mode - Duramax 6.6L V8 Turbo Diesel (GM HD, L5P 2017+ generation)

Injector wear / pigtail-connector misfires

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

Symptoms

rough idle, hard starting, poor fuel economy, excessive exhaust smoke (a parts retailer's symptom table)
misfires traced to injector pigtail/connector faults rather than the injector body (community)

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

Root cause

Denso common-rail injectors on the L5P fail uncommonly compared with earlier Duramax generations - failures tie to very high mileage or contaminated fuel rather than a design flaw. Connector/pigtail faults produce the same drivability picture and should be ruled out first.

Diagnosis

cylinder-contribution/balance test before ordering injectors; inspect pigtails and connectors for heat damage
on a high-miler with a contamination history, plan for the full high-pressure circuit, not just one injector

Fixes

repair connectors/pigtails where faulty; replace injectors in the documented sets when contribution tests fail ()

Prevalence

occasional