ASVAB · Ignition and Fuel Systems

What is the function of the spark plug in a gasoline engine?

Reviewed by Jordan Morley, Editorial Lead at 247SimpleTests. Written by the 247SimpleTests Editorial Team from the official source material cited on every question.

Correct answer

To ignite the compressed air-fuel mixture in the cylinder

A To ignite the compressed air-fuel mixture in the cylinder
B To filter the oil
C To cool the engine
D To pump fuel

Why this is the answer

The spark plug ignites the compressed air-fuel mixture in the combustion chamber by creating an electric spark at precisely the right moment. This ignition causes the controlled explosion that drives the piston down during the power stroke. Spark plugs are part of the ignition system in gasoline engines (diesel engines instead rely on compression heat to ignite the fuel and don't use spark plugs). Fouled or worn spark plugs cause misfires and poor performance. Knowing the spark plug's role in igniting the mixture is essential ignition-system knowledge.

Source: ASVAB Auto Information — Spark Plugs

Practice more questions

This question is from our ASVAB Practice Tests practice test. Take the full practice test to test your knowledge across all Ignition and Fuel Systems and other topics.

Take the Auto Information practice test →

About this topic: Ignition and Fuel Systems

Ignition and fuel questions cover how spark plugs, coils and the firing order deliver a spark at the right moment, and how fuel injection, pumps and filters deliver fuel. Symptoms of a fault in each system are a favourite question type. This is one of 8 Auto Information questions on ignition and fuel systems, each with a full explanation on a single study page.

New to this exam? Our ASVAB exam guide explains the format, scoring, and how to prepare.

Recommended study materials

Study guide

As an Amazon Associate, CJ Affiliate, and AWIN publisher we earn from qualifying purchases. Links above are affiliate links. Full disclosure →

What is the function of the spark plug in a gasoline engine?

Why this is the answer

Practice more questions

About this topic: Ignition and Fuel Systems

Related questions

What is the primary function of a spark plug?

Modern gasoline engines use what system to deliver fuel into the engine?

What is the function of a vehicle's exhaust system?

If a car has trouble starting in cold weather, which is the LEAST likely cause?

Recommended study materials

ASVAB Total Prep (Kaplan)

Barron's ASVAB with Online Tests 12th Ed.

ASVAB for Dummies 4th Ed. (Wiley)