NCED Engine Performance & Tuning 2

Question 1

What does AFR stand for in the context of engine tuning?

Accepted Answer

Air-Fuel Ratio

Answer

AFR (Air-Fuel Ratio) describes the mass ratio of air to fuel in the combustion mixture, which directly affects power, efficiency, and emissions.

Question 2

What is the stoichiometric air-fuel ratio for a gasoline engine?

Accepted Answer

14.7:1

Answer

The stoichiometric ratio for gasoline is 14.7:1, meaning 14.7 parts air to 1 part fuel, which achieves complete combustion with no excess oxygen or unburned fuel.

Question 3

What is engine knock (detonation) caused by?

Accepted Answer

Uncontrolled auto-ignition of the air-fuel mixture before the spark plug fires

Answer

Knock occurs when portions of the air-fuel mixture ignite spontaneously from heat and pressure rather than from the spark plug, causing pressure waves that can damage pistons and bearings.

Question 4

Advancing ignition timing means the spark plug fires:

Accepted Answer

Earlier in the compression stroke

Answer

Advancing timing fires the spark plug earlier in the compression stroke, giving the mixture more time to fully combust by the time the piston reaches TDC, which can increase power but risks knock.

Question 5

What does a Mass Air Flow (MAF) sensor measure?

Accepted Answer

The mass of air entering the engine per unit time

Answer

The MAF sensor measures the mass flow rate of air entering the engine, allowing the ECU to calculate the correct fuel quantity for the desired air-fuel ratio.

(NCED) Nationally Certified Educational Diagnostician Practice Test

(NCED) Nationally Certified Educational Diagnostician Practice Test

NCED Engine Performance & Tuning 2