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

Reliability build

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

Fuel-system health for the L5P (modes Fuel contamination damage to the HP4/injector system (no CP4 on the L5P) / In-tank lift pump / low-pressure fuel delivery stalls): the Denso HP4 does not carry the CP4's catastrophic failure pattern, but it is not contamination-proof - dirty fuel still kills the pump and injectors. The prevention is boring and total: the two-filter cycle on schedule (primary WIF + main), and the in-tank lift pump watched, not feared.

Parts

• Duramax L5P Fuel Filter Service Kit (OEM) - the filter service kit - run it on schedule, this IS the prevention (qty 1)
• Duramax L5P Fuel/Water Separator Filter (OEM) - primary filter with water-in-fuel sensing (13543066) (qty 1)
• Duramax L5P Main Fuel Filter (OEM) - main filter (84996837) (qty 1)
• Duramax L5P In-Tank Transfer (Lift) Pump (OEM) - in-tank lift pump if pressure tests low - starvation shows up as HP4/injector wear later (qty 1)
• Duramax L5P Fuel Pump Power Control Module (OEM) - pump controller/driver side before blaming the pump itself (qty 1)

Install order

1. adopt the two-filter cycle and log WIF events - the prevention is the schedule, not a part
2. low-pressure complaint: test the lift-pump circuit and controller before the pump
3. any contamination event: full filter set, tank check, and a documented pump/injector assessment

Expected outcome

Clean fuel to a $17k investment; no starvation stories.

Do not

• do not stretch the filter cycle on this engine - the HP4 is cheaper than a CP4 event but still four figures

Parts budget

About $50-$85 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.

• about $50: Duramax L5P Fuel Filter Service Kit (OEM) (about $50)
• about $80: Duramax L5P Fuel/Water Separator Filter (OEM) (about $80)
• about $85: Duramax L5P Main Fuel Filter (OEM) (about $85)
• about $85: Duramax L5P In-Tank Transfer (Lift) Pump (OEM) (about $85)
• about $85: Duramax L5P Fuel Pump Power Control Module (OEM) (about $85)

DIY or shop: DIY for filters and lift pump; contamination events are shop-grade.