CEI CEI Fuel Systems & Engine Combustion 2

Question 1

Which sensor provides feedback to the engine control unit (ECU) to maintain the air-fuel ratio near stoichiometry and is critical for three-way catalytic converter efficiency?

Accepted Answer

Oxygen (O2) sensor / lambda sensor

Answer

The oxygen sensor (lambda sensor) measures oxygen content in the exhaust, allowing the ECU to perform closed-loop fuel corrections to keep the A/F ratio at stoichiometry for optimal catalytic converter performance.

Question 2

A vehicle shows high positive fuel trim values (e.g., +25%) at idle. What does this most likely indicate?

Accepted Answer

An unmetered air leak (vacuum leak) causing the ECU to add extra fuel to compensate for a lean condition

Answer

High positive fuel trim means the ECU is adding significantly more fuel than normal, typically because unmetered air (from a vacuum leak) is leaning out the mixture and the ECU compensates.

Question 3

What type of fuel system does a 'direct injection' gasoline engine use, and what emission challenge is uniquely associated with it?

Accepted Answer

Fuel is injected directly into the combustion chamber, which produces higher particulate matter (PM) emissions compared to port injection

Answer

Gasoline direct injection (GDI) injects fuel directly into the cylinder, improving efficiency but producing more ultrafine particulate matter due to incomplete fuel-air mixing before ignition.

Question 4

What is 'engine knock' (detonation), and how does it affect exhaust emissions?

Accepted Answer

Uncontrolled auto-ignition of the air-fuel mixture before the spark plug fires, causing incomplete combustion and increased HC and CO emissions

Answer

Engine knock (detonation) occurs when the air-fuel mixture ignites spontaneously before the spark event, causing uneven combustion that increases unburned HC and CO emissions.

Question 5

In a diesel engine, what is the primary pollutant of concern that is significantly higher than in gasoline engines due to the nature of diesel combustion?

Accepted Answer

Particulate matter (PM) and NOx

Answer

Diesel engines produce significantly more particulate matter (soot/PM) and NOx than gasoline engines due to their high-temperature, lean, heterogeneous combustion process with fuel-rich zones.

CEI - Certified Emission Inspector Practice Test

CEI - Certified Emission Inspector Practice Test

CEI CEI Fuel Systems & Engine Combustion 2