GASOLINE MODELS
The crankcase ventilation system is designed to return blow-by gases to engine through the intake manifold and air cleaner. Gasoline models use a PCV valve to control blow-by flow.
During part throttle engine operation, intake vacuum pulls blow-by gases through PCV valve. Capacity of valve is enough to handle blow-by gas plus some ventilating air. Ventilating air is drawn from carburetor air cleaner, or from air duct on fuel injected models, and into crankcase through connecting tube.
During wide open throttle, manifold vacuum is not sufficient to draw blow-by gases through valve. These gases then go through tube to air cleaner in a reverse direction. Engines with excessive blow-by will pass crankcase gases through tube to carburetor during all operating conditions.
Crankcase Ventilation System (Pickup - Gasoline) Note direction of flow. Scheme 2
Crankcase Ventilation System (200SX) Note direction of flow. Scheme 3
Crankcase Ventilation System (300ZX, Maxima) Note direction of flow. Scheme 4
Crankcase Ventilation System (Pulsar NX & Sentra) Note direction of flow. Scheme 5
Crankcase Ventilation System (Stanza) Note direction of flow. Scheme 6
DIESEL MODELS
The diesel models use a closed crankcase ventilation system which prevents blow-by gases from entering the atmosphere. A crankcase emission control valve keeps crankcase pressure constant.
During part throttle engine operation, blow-by gas pressure opens the control valve allowing gases to flow through a connecting hose to intake manifold for burning. When the throttle is closed, the control valve reduces flow rate so engine will not draw in dust and air around crankshaft oil seal.
Crankcase Ventilation System (Diesel Sentra Shown; Diesel Pickup Similar) Note direction of flow. Scheme 7
MAINTENANCE
Service crankcase ventilation system every 30,000 miles or every 2 years. Perform this maintenance more frequently if vehicle is operated in dusty conditions.
Test PCV valve operation and check ventilation hoses and connections for leaks and obstructions. Disconnect all hoses and clean with compressed air.
On models equipped with a flame arrester, ensure that arrester is installed in hose between valve cover and air duct.
PCV VALVE
With engine running at idle, remove ventilation hose to crankcase from PCV valve and check that air flows through PCV valve. Place finger over PCV valve inlet and a strong vacuum will be felt if valve is operating properly.
DIESEL CRANKCASE EMISSION CONTROL VALVE
- Remove crankcase emission control valve from valve cover. Apply vacuum to control valve's intake air duct port. (Scheme 7) Check that air flows up through valve's port to valve cover.
- Place thumb over valve cover port on control valve and again apply vacuum to other port. If valve is operating properly, it will click when vacuum is applied.