Failure mode - Ford 7.3L Power Stroke Diesel (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)

Compare with the other causes of the same sign on this engine: misfire, rough idle, hesitation or surging (4 causes)

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 - more than one option: 7.3L Power Stroke Internal Injector Harness 1994-1997 (aftermarket), 7.3L Power Stroke Under-Valve-Cover Harness 1999-2003 (OEM)

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

7.3L Power Stroke Valve Cover Connector Pigtails (Alliant AP0015 OBS / AP0016 99-03)

Prevalence

common

Parts for this repair run about $55-$160: see them next to the other repairs on this engine in repair costs.