It's almost always bad fuel quality and especially the presence of water that "kills" injectors. Water actually screws up the spray pattern by wearing the metal in the nozzel openings. That's why the "100,000 mile fuel injector check" is only estimate of when to pull the injectors. Many truck fleets just do this at about 100,000 miles as regular maintenance, while other truck owners wait till they start to see more smoke than usual. The test is so simple, there's no reason not to get it done. It's cheap insurance.
