Positive Crankcase Ventilation Valve and Secondary Air-Injection Systems Chapter 27 Part One

How does the computer know the PCV failed?

Check the MAF airflow and compares to specs

What happens to the PCV valve when the engine back fires?

Close instantly

What is the main reason we cannot let the blow-by into the atmosphere?

Hydrocarbons from blow-by pollute the atmosphere

Why is the PCV valve sometimes reffered to an anti-back fire valve?

Prevents the backfire from entering the crankcase

Explain the PCV valve rattle test.

Remove PCV, rattle PCV

When the intake manifold vacuum is high, such as idle, and light loads the PCV valve ______ to maintain a balance air-fuel ratio.

Restricts airflow

What is blow by?

When gases and unburned fuel leak past the piston ring

List the components of the PCV system.

1. PCV valve or calibrated orifice 2. PCV inlet air filter and hoses

Exlain the PCV valve 3x5 card test.

1. Place 3x5 card over oil fill opening 2. Card should be pulled by vacuum

Explain the PCV Snap-back test.

1. Placing finger over inlet hose rapidly 2. When engine running, valve should snap back and forth if working properly

List four problems that can occur if the PCV system is blocked or plugged.

1. Rough/unstable idle 2. Excessive oil consumption 3. Oil in air filter housing 4. Oil leak due to excessive crankcase pressure

Describe three locations where the orifice may be located?

1. Valve cover 2. Intake manifold 3. In a hose connected to valve cover

What percentage of air coming into the engine at idle flows through the PCV valve?

30%

What can cause a whistling sound from the rear main seal?

A plugged PCV valve vent creating vacuum in crankcase

Why are there wires on a Ford PCV valve?

Electric heater to prevent ice from forming inside PCV valve

Under ______ the spring in the PCV pushes the valve open and allows maximum airflow.

High speed and heavy loads

What causes the PCV to flow less at idle?

High vacuum pulls the valve to restrict flow

Where is the PCV valve located?

In the valve cover or intake manifold

In most systems what does the PCV contain?

One-way valve containing a spring operated plunger

On turbo engines what type of crankcase ventilation is used?

Oil/vapor separator

What can cause an engine to leak oil only when the engine is off?

PCV prevents oil when its running because vacuum is created in crankcase

Why cause the 3x5 card vibrate on 4 cylinder engines and not 6 or 8 cylinders?

The time intervals between intake strokes on a four cylinder engine

Why does the GM clip the heater hose to the PCV valve?

To prevent ice blockage in freezing weather

What is the purpose of the positive crankcase ventilation system?

To recirculate the vapors into induction system

Describe what is an engine back fire?

Unburnt hydrocarbons ignite in exhaust or intake

What should be done if the engine fail the 3x5 card test?

Verify with another test