Failure mode - Ford 7.3L Power Stroke (T444E)

Under-valve-cover harness (UVCH) failure

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

Symptoms

rough running / dead hole(s); misfire that comes and goes
glow plugs reading dead on a scanner (harness, not plugs)
melted/burnt connector at the valve cover (9/16' run through the gasket)

Root cause

The injector/glow-plug harness runs through the valve cover gasket (two connectors per bank 1994-1997, one per bank 1999-2003); chafe, heat and connector loosenness drop injectors or glow plugs. A huge share of 'my 7.3 runs rough' threads end at the UVCH.

Diagnosis

scan glow-plug circuit resistance per bank: open circuit = harness or plug, not GPR
inspect the exterior connectors at the valve covers for melt/looseness
wiggle-test harnesses while running to reproduce a dropout

Fixes

replace the UVCH / valve-cover gasket-integrated harness (correct 2-connector OBS or 1-connector 99-03 design) ()

uvch-harness (part category - specific model not chosen)

replace exterior under-cover connectors/pigtails at the same time if heat-checked ()

uvch-connector-pigtail (part category - specific model not chosen)

Prevalence

common