Failure mode - Ford 7.3L Power Stroke Diesel (T444E)

Injector o-ring failure

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

Symptoms

blue/gray smoke at startup clearing as it warms
oil consumption with no external leak
high-pressure-oil symptoms if the lower o-rings leak (hard start hot)

Compare with the other causes of the same sign on this engine: hard start, long crank or no-start (7 causes) · blue or gray smoke (burning oil) · oil leak, oil consumption or rising oil level (2 causes)

Root cause

HEUI injectors seal combustion, fuel AND high-pressure oil with stacked o-rings; age hardens them. Smoke at startup = upper o-rings; hot-start pressure loss = lower o-rings. Injector service codes are era-specific (AA single-shot 49-state OBS / AB split-shot California 96-97 / AE long-lead cyl-8 99+).

Diagnosis

blue smoke at cold start that clears = upper injector o-rings (classic signature)
cylinder-balance/contribution test to find the weak hole
o-ring kit first (cheap) if the injector itself balances out

Fixes

injector o-ring kit (full set, all 8) - the first-line fix ()

7.3L Power Stroke HEUI Injector Seal Kit (aftermarket)
injector - more than one option: 7.3L Power Stroke HEUI Injector AA code 1994-1997, 7.3L Power Stroke HEUI Injector AB code 1996-early 1999, 7.3L Power Stroke HEUI Injector AD/AE code 1999.5-2003

replace/reman injectors with correct-era code (AA/AB/AE; cyl-8 long-lead on 99+) ()

injector - more than one option: 7.3L Power Stroke HEUI Injector AA code 1994-1997, 7.3L Power Stroke HEUI Injector AB code 1996-early 1999, 7.3L Power Stroke HEUI Injector AD/AE code 1999.5-2003

Prevalence

common

Parts for this repair run about $10-$630: see them next to the other repairs on this engine in repair costs.