Forced crankcase ventilation system (Mazda Capella GC)

Contents: Technical condition check ⇓ Replacement of elements ⇓

Figure 8.4. Diagram of the forced crankcase ventilation system: 1 – suction pipe; 2 – air filter; 3 – spool valve; 4 – cylinder head cover; 5 – fresh air; 6 – crankcase gases; 7 – fuel-air mixture

Forced crankcase ventilation reduces the hydrocarbon content of exhaust gases by circulating fresh air through the crankcase, mixing it with crankcase gases and directing this mixture into the intake manifold for afterburning in the engine combustion chamber (figure 8.4).

The system consists mainly of vacuum hoses and a valve device that regulates the flow of gases in accordance with the engine crankshaft speed and the degree of vacuum in the intake manifold.

Technical condition check

The functionality of the crankcase ventilation system can be easily checked.

This system needs to be checked regularly as the valve and vacuum hoses tend to become clogged with soot and resinous deposits from the exhaust gases. When the flow through the valve decreases or stops, the engine idle speed usually decreases and the engine runs unsteadily at idle.

To check the vacuum in the system, remove the air cleaner cover and locate the small PCV filter, which is located on the inside of the air cleaner housing.

Disconnect the hose going to this filter.

With the engine idling, close the opening of the hose with your thumb – you should feel a slight vacuum. If you gradually move your finger away, you can hear a hissing sound. This indicates that air is being sucked throughout the entire system line. If a vacuum is felt, the system is working properly. Check the cleanliness of the filter element. If you suspect that the filter element is dirty, replace it, as this is an inexpensive operation that ensures safety during engine operation.

If the vacuum at the end of the hose is weak, then the system line is clogged and requires further inspection.

Turn off the ignition, locate the ventilation valve and carefully remove it from the rubber boot. Shake the spool and listen for the resulting sound like knocks (clicks). Knocks are caused by the spool ball. If the knocking sounds do not occur with every shaking (the knock is not free), replace the spool.

Start the engine and let it idle with the valve stem removed. Close the valve opening with your thumb and check the vacuum. It should be significant and felt immediately.

If the vacuum at the valve is weak or not felt at all, turn off the ignition and disconnect the vacuum hose from the other end of the valve. Start the engine and, at idle, check the vacuum at the end of the hose that is disconnected from the valve. Lack of vacuum indicates contamination inside the hose or engine intake pipe. If the hose is clogged, replace it or remove it from the engine and blow it out with compressed air. If the carburetor or intake manifold passages are clogged, these components must be removed and thoroughly cleaned to remove resinous deposits. If the vacuum on the hose without the valve is strong, and at the valve input with the hose connected it is weak, the valve is faulty and needs to be replaced.

When purchasing a new PCV valve, make sure it is the correct part for your engine type. Otherwise, too little or too much vacuum may occur, which may result in engine failure.