Exam 34: Emission Control Diagnosis and Service

Technician A checks a PCV valve by sucking air through it with his mouth. Technician B checks a PCV valve by removing the valve from the grommet in the valve cover and placing his finger over the end of the valve to check for vacuum. Who is correct?

Technician A says retrieving DTCs from the control system is the best beginning for diagnosing emission problems. Technician B says because a single emissions system component failure can set multiple DTCs, codes should be used only to confirm the effectiveness of the repairs. Who is correct?

What will result from too little EGR flow?

Technician A says if the EVAP system is purging vapors from the charcoal canister while the engine is idling, rough engine operation will occur. Technician B says the system should not have more than 0.5 liter of flow during the 240 seconds of an I/M 240 test. Who is correct?

High ___________________ emissions are associated with an inoperative EGR valve.

If the PCV valve is stuck in the open position, a lean air/fuel ratio may cause a rough idle or engine stalling.

A PCV valve that is stuck closed or a restricted hose can cause an accumulation of moisture and sludge in the engine.

A restricted or plugged ___________________ system may cause excessive HC and CO emissions.

Excessively high HC emissions may be caused by ______.

Which of the following gases is NOT considered to be harmful?

A typical four-gas exhaust analyzer does not measure ____ emissions.

Excessively high ____________________ emissions can be caused by any condition that prevents the EGR from allowing the correct amount of exhaust gases to enter the cylinders.

A catalytic converter can be tested with a rubber mallet.

An excessively lean air/fuel ratio resulting in misfires causes HC emissions to ____________________.

Technician A says CO emissions increase as the air/fuel ratio becomes richer. Technician B says CO emissions increase as the air/fuel ratio becomes leaner. Who is correct?

Technician A says when CO goes up, O₂ goes down. Technician B says at the stoichiometric point (14.7:1), HC and CO will be at their lowest levels and CO₂ will be at its highest. Who is correct?

What tool is needed to test vacuum-type EGR valves?

Low CO indicates a lean mixture; as the mixture becomes more lean, HC increases.

A restricted catalytic converter may cause ______.

Poor EGR gas flow can cause detonation (spark knock).