Failure mode - Ford 6.0L Power Stroke

Marginal regulated fuel pressure (blue spring)

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

Symptoms

not a discrete failure: a known weak point
regulated pressure that sits low (community reports roughly 45-55 psi with the factory yellow spring)
over time, shortened injector life - in the HEUI design the diesel fuel is also the injector's coolant and lubricant, so chronic low pressure means less cushioning of the internals
power loss or hesitation under load, especially with a tune or upgraded injectors

Root cause

The factory fuel pressure regulator spring (yellow) targets a low pressure. Lift-pump (HFCM) capacity and fuel-filter restriction pull it lower under demand. Because the fuel doubles as the injector spool-valve coolant and lubricant, running the injectors chronically underfed is widely held to shorten their life; below roughly 45 psi is called a danger zone, and dips below ~40 psi at wide-open throttle are described as actively damaging the injectors through cavitation.

Diagnosis

install a fuel pressure gauge at the secondary filter / regulator test port
read pressure at idle and at wide-open throttle: independent sources put the healthy window at roughly 55-65 psi under load, concern below ~45, active injector damage below ~40 at WOT
fresh fuel filters before judging

Fixes

blue spring upgrade kit (raises regulated pressure roughly 10 psi) ()

fuel-regulator-blue-spring-kit (part category - specific model not chosen)

regulated-return / deadhead relocation kit for a cleaner reading and higher flow ()

fuel-regulator-deadhead-kit (part category - specific model not chosen)

upgraded lift pump for higher-power builds; fresh fuel filters ()

lift-pump (part category - specific model not chosen)
fuel-filter-set (part category - specific model not chosen)

Prevalence

near-universal