Core Concepts and Principles Flashcards

In a four-stroke engine, during which stroke are both valves closed while the piston moves upward to squeeze the air-fuel mixture?

Answer: Compression

During the compression stroke both valves are closed and the rising piston compresses the charge before ignition.

What does an engine's compression ratio describe?

Answer: Ratio of total cylinder volume at BDC to combustion chamber volume at TDC

Compression ratio compares cylinder volume with the piston at bottom dead center to the volume left at top dead center.

On transverse-engine VW 4MOTION vehicles such as the Golf R or Tiguan, what typically sends torque to the rear axle?

Answer: An electronically controlled multi-plate clutch coupling (Haldex type)

Transverse 4MOTION systems use a Haldex-type electro-hydraulic multi-plate clutch to vary torque sent to the rear axle.

What is VW Group's official dealer-level diagnostic software platform?

Answer: ODIS

ODIS (Offboard Diagnostic Information System) is the VW Group dealer diagnostic and programming software.

When performing a voltage drop test on a starter circuit, what condition must the circuit be in?

Answer: Loaded and operating (cranking)

Voltage drop shows up only when current flows, so the circuit must be under load during the test.

Why is timing belt replacement on schedule especially important on an interference engine?

Answer: If the belt breaks, valves can contact the pistons and cause major damage

In an interference engine, valves and pistons share space, so a belt failure can bend valves and damage pistons.

What is the stoichiometric air-fuel ratio for gasoline, which corresponds to lambda = 1?

Answer: 14.7:1

Gasoline burns completely at about 14.7 parts air to 1 part fuel by mass, defined as lambda 1.