Failure mode - Cummins 6.7L ISB (Ram HD)

Injector 'chuffing' / seal blow-by

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

Symptoms

audible 'chuff chuff' exhaust beat (compressed gas past an injector's copper seal)
fuel in the oil / rising oil level (pairs with the oil-dilution mode)
fuel smell, smoke, rough cylinder balance; balance-rate DTCs

Root cause

High-pressure gas leaks past worn injector copper sealing washers (audible chuff) or internally worn injectors; either path can push fuel into the oil. Bostech: service PNs differ between pickups and chassis cabs - order by application. Common-rail injector health ties back to fuel filtration and water intrusion.

Diagnosis

cylinder-balance / contribution test to locate the weak hole
listen at the exhaust for the chuff beat; check oil level trend for dilution
return-flow / leak-back test per injector where equipped
inspect fuel filters / water-in-fuel history (water destroys CR injectors)

Fixes

replace copper sealing washers (cheap) if the injector itself tests healthy ()

injector-seal-kit (part category - specific model not chosen)

replace injectors with correct-application units (pickup vs chassis-cab service PNs differ) ()

injector (part category - specific model not chosen)

fuel filtration and water drainage discipline to protect the new set ()

fuel-filter (part category - specific model not chosen)

Prevalence

common