Crankcase Ventilation System Inspection/Diagnosis

Crankcase Ventilation System Diagnosis
With this system, any excessive blow-by in system (from a badly-worn engine, a sustained heavy load, etc.) is exhausted into intake manifold and is drawn into engine. A proper operation of the PCV system is dependent upon a sealed engine. If oil sludging or dilution is noted, and PCV system is functioning properly, check engine for other causes and correct as necessary in order to ensure that system functions as intended.

Crankcase Ventilation System Functional Test

Functional Check of the Positive Crankcase Ventilation (PCV) System
1. Disconnect the Positive Crankcase Ventilation (PCV) hose.
2. Start the engine.
3. Check for vacuum at the hose. If there is no vacuum, check for a plugged hose or manifold port.
4. Check for a hose that collapses when blocked (vacuum applied). Replace the plugged or deteriorated hoses.
5. Allow the engine to idle at the normal operating temperature.
6. Remove the engine oil dipstick and install a vacuum gage on the dipstick tube.
7. Block off the PCV system fresh air intake passage.
8. Run the engine at 1,500 RPM for 30 seconds, then read the vacuum gage while the engine is running at 1,500 RPM.
If a vacuum is present, this indicates that the crankcase ventilation system is functioning properly. No vacuum indicates that the engine may not be sealed and is drawing in outside air. Check the valve covers, oil pan gasket, or other sealing areas for leaks. If the vacuum gage registers a positive pressure through the dipstick tube, check for a plugged hose or engine blow-by.
Results of Incorrect Operation A plugged PCV hose may cause the following conditions:
^ A rough idle
^ Stalling or a slow idle speed
^ Oil leaks
^ Sludge in the engine
A leaking hose would cause the following conditions:
^ A rough idle
^ Stalling
^ A high idle speed

Theory of Operation
The PCV system flows fresh air into the engine crankcase to dilute the unburned hydrocarbons present and route them into the intake manifold where they are consumed during the combustion process.

Crankcase Ventilation System Inspection/Diagnosis
1. Disconnect the Positive Crankcase Ventilation (PCV) hose.
2. Start the engine.
3. Check for vacuum at the hose. If there is no vacuum, check for a plugged hose or manifold port. (check for a hose that collapses when blocked (vacuum applied). Replace the plugged or the deteriorated hoses.
4. Allow the engine to idle at normal operating temperature.
5. Remove the engine oil dipstick and install a vacuum gage on the dipstick tube.
6. Block off the PCV system fresh air intake passage.
7. Run the engine at 1,500 RPM for 30 seconds, then read the vacuum gage while the engine is running at 1,500 RPM.
^ If vacuum is present, this indicates that the crankcase ventilation system is functioning properly.
^ If no vacuum is indicated, the engine may not be sealed and is drawing in outside air. Check the valve covers, the oil pan gasket or other sealing areas for leaks.
^ If the vacuum gage registers a pressure, or if a vacuum gage is pushed out of dipstick tube, check for a plugged PCV port, a plugged hose or an excessive engine blow-by.