CPT Engine Performance & Tuning 4

Question 1

What does a manifold absolute pressure (MAP) sensor measure?

Accepted Answer

Absolute pressure inside the intake manifold

Answer

The MAP sensor measures the absolute pressure in the intake manifold, which the ECU uses to calculate engine load for fuel and timing control.

Question 2

A technician notices that idle quality improves when a specific injector is unplugged. This finding most likely indicates:

Accepted Answer

That injector is leaking or flowing too much fuel

Answer

Removing a leaking or over-fueling injector from the circuit reduces the rich condition it was creating, thereby improving idle quality.

Question 3

Which condition would cause a scan tool to display a negative short-term fuel trim (STFT) value?

Accepted Answer

Rich condition detected by the O2 sensor

Answer

The ECU pulls fuel trim negative (reduces fuel delivery) when the O2 sensor indicates a rich exhaust mixture.

Question 4

A restricted fuel injector will most noticeably degrade performance under which condition?

Accepted Answer

Wide-open throttle (WOT) at high RPM

Answer

At WOT and high RPM, maximum fuel delivery is demanded; a restricted injector cannot supply adequate flow, causing lean misfire and power loss.

Question 5

What is volumetric efficiency (VE) a measure of in an internal combustion engine?

Accepted Answer

How effectively the engine fills the cylinder with fresh charge compared to theoretical maximum

Answer

VE compares actual air mass ingested per cycle to the theoretical maximum based on displacement, reflecting how well the engine breathes.

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