See Figure 1
The Crankcase Depression Regulator (CDR), found on 1982 and later diesels is designed to scavenge crankcase vapors in basically the same manner as the PVC valve on gasoline engines. The valves are located either on the left rear corner of the intake manifold (CDR). On this system there are two ventilation filters, one per valve cover.
The filter assemblies should be cleaned every 15,000 miles (24,135 km) by simply prying them carefully from the valve covers (be aware of the grommets underneath), and washing them out in solvent. The ventilation pipes and tubes should also be cleaned. The CDR valve should also be cleaned every 30,000 miles (48,270 km)-the cover can be removed from the CDR. Dry each valve, filter, and hose with compressed air before installation.
Do not attempt to test the crankcase controls on these diesels. Instead, clean the valve cover filter assembly and vent pipes and check the vent pipes. Replace the breather cap assembly every 30,000 miles (48,270 km). Replace all rubber fittings as required every 15,000 miles (24,135 km).