Ch. 27 Pt. 1/2

How does the computer know the PCV valve has failed?

Checkes MAF sensor and compares to data in ROM

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

Prevents back fire from entering crankcase

What is the purpose of the positive crankcase ventilation system?

Recirculate the blow by vapors to engines induction system.

Explain the PCV valve 3x5 card test:

Remove oil cap, place 3x5 card over oil filler hole at idle, it should suck in

Explain the PCV valve rattle test:

Shake valve, if there is no rattle the PCV should be replaced.

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

Prevent freezing

List the components of the PCV system:

- PCV valve or orifice - Air filter and connecting hoses

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

- Rough or unstable idle - Excessive oil consumption - Oil in air filter housing - Oil leaks due to pressure in crank case

Describe three locations where the orifice may be located?

- Valve Cover - Intake Manifold - Between the valve cover and air cleaner

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

30%

In most systems what does the PCV contain?

A oneway valve containing a spring operated plunger.

Where is the PCV valve located?

Between valve cover and intake manifold.

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

Blow by contains hydrocarbons and carbon monoxide.

What is blow by?

Gases leaking past the rings.

What speed has the most flow through the PCV Valve? - Idle Speed - High Speed - Backfire

High Speed

What causes the PCV to flow less at idle?

High manifold vacuum pulls the valve to restrict flow

On turbo engines what type of crankcase ventilation is used?

Oil separator and orifice

In the diagram from the homework, does this ventilation use a valve or orifice? What is component 101 called?

Orifice, Oil vapor separator

Explain the PCV snap-back test:

Place finger over inlet hole in valve with engine running and removing finger rapidly. Valve should snap back and forth.

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

Plugged PCV vent causing vacuum in the crank case

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

The PCV valve creates a vacuum in the crankcase when engine is running

Why cause the 3x5 card vibrate on 4 cylinder engines and not on a 5 or cylinders?

The time intervals between intake strokes on a 4 cylinder engine.

Describe what is an engine back fire.

Unburned hydrocarbons ignite in exhaust or intake

Why are there wires on Ford PCV valves?

Used for electric heater

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

Valve closes instantly

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

Verify with another test

Under ___ the spring in the PCV pushes the valve open and allows maximum flow.

high speeds or heavy loads

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