Replace your old and dirty air filter with a Drop-In Air Filter for your 1989-1993 Dodge 5.9L 12V Cummins. In most cases an oe-style drop-in air filter will be made with paper filter media, where an aftermarket air filter typically features a synthetic media, or a cotton gauze design that may be dry or oiled. Find drop-in filters from manufacturers like S&B Filters, AFE, K&N Engineering, and others at XDP. A drop-in air filter is named after the simple installation procedure as it simply drops into the factory airbox in most applications. Air Filters provide your engine with clean air by trapping harmful contaminants such as dust and debris before entering the intake.