Positive Crankcase Ventilation: Testing and Inspection

SYSTEM QUICK CHECK

A quick check of the system can be made by pulling the end of the valve out of the valve cover and, with the engine idling, placing a finger over the end of the valve to block the air flow. A vacuum should be felt and the engine speed should drop approximately 50 RPM if the system is satisfactory. If there is no change in engine speed a clogged system is indicated. To isolate the problem, remove the valve from the hose. If the ventilation hoses and carburetor passages are clear, a strong vacuum will be felt as the hose is uncovered. If this occurs, the trouble is in the valve. If the engine continues to idle approximately as it did before the hose was uncovered, the hoses or carburetor passages are blocked.

PCV VALVE TEST

1. Install a PCV valve known to be good in the crankcase ventilation system.
2. Start engine and compare engine idle condition to the prior idle condition.
3. If the loping or rough idle condition remains when the good PCV valve is installed, the crankcase ventilation system is not at fault. Further engine component diagnosis will have to be made to find the cause of the malfunction.
4. If the idle condition proves satisfactory, replace the PCV valve and clean hoses, fittings, etc.