Cummins Injector Tech Video For L10, M11 & N14 Engines 

Non stop as in at idle, cruise, full load? And is it a STC L10 or fixed time? STC engines will smoke all the time if the STC valve is stuck.

@@speedandmarine9066 thank you. It was sold by the customer about a year ago, not long after I asked. Truck ran great minus the smoke... smoke would clear up a bit as the motor warmed up, but it was always present to some degree.

@@WeldingInformation Couple of things could cause that, but it sounds like an STC engine that the STC valve was stuck and the low speed timing never shifted to "fast time" (aka advanced). Not an uncommon problem on any STC Cummins, especially if they don't get regular maintenance. Hard to say without doing some checking, but since the truck is sold it's just a guess. If this is the case the smoke would be worst just after a cold start and get better with temp. Probably would always smoke a bit at idle and low rpm accel would smoke too. Once up on boost smoke would probably cleared up to "normal" levels.