Positive Crankcase Ventilation (PCV) System Monitoring

Description







The crankcase is vented via the oil drain passages in the cylinder blocks and cylinder heads and two ports in each camshaft cover. Pipes connect the larger ports in the camshaft covers to the intake duct on the upstream side of the throttle disc. The smaller ports in the camshaft covers are connected to the inlet manifold, downstream of the throttle body, also by pipes. Each of the smaller ports incorporates a restrictor and a gauze oil separator to prevent oil being drawn out of the camshaft covers with the blow-by gases.

When the engine is running with the throttle disc closed or partially open, the depression downstream of the throttle disc draws crankcase gases into the inlet manifold through the smaller ports or restrictors in the camshaft covers. Clean air, from the upstream side of the throttle disc, is drawn into the crankcase through the larger ports in the camshaft covers to limit the depression produced in the crankcase. When the engine is running with the throttle disc wide open both the upstream and downstream sides of the throttle disc are subjected to similar, relatively weak, depression levels. So crankcase gases are then drawn out of both ports in each camshaft cover, with the majority being drawn out of the unrestricted larger ports and into the throttle body.

Disconnection of the part-load breather, i.e. one of the pipes from the small ports in the cam covers, is likely to result in a tendency of the engine to stall when returning to idle and the quantity of un-metered air, which flows into the intake manifold will result in the detection of fuel system faults by the OBD system. Flow through the larger pipes is negligible under normal driving, but the diagnostic system will detect a fault due to the presence of un-metered air under certain driving conditions.

For these reasons, there are no separate monitors for compliance with the requirements of PCV monitoring.