Car Tuning Fuel and Ignition Management 2

Question 1

What does a wideband O2 sensor measure that a narrowband sensor cannot?

Accepted Answer

Exact air-fuel ratio across a wide lambda range

Answer

A wideband O2 sensor can accurately measure lambda from approximately 0.7 to 32, whereas a narrowband only indicates rich or lean near stoichiometry.

Question 2

When tuning a turbocharged engine, why is ignition timing typically reduced at high boost levels?

Accepted Answer

To prevent detonation caused by higher combustion temperatures and pressures

Answer

Higher boost increases charge density and temperature, making the mixture more prone to knock, so timing must be retarded to keep combustion safe.

Question 3

What is 'closed-loop' fuel control?

Accepted Answer

The ECU uses O2 sensor feedback to correct fuel trims in real time

Answer

In closed-loop operation the ECU reads the O2 sensor and adjusts short-term fuel trims to maintain the commanded air-fuel ratio.

Question 4

A tuner notices positive long-term fuel trims (LTFT) of +18% at idle. What does this most likely indicate?

Accepted Answer

A vacuum leak or lean condition the ECU is compensating for

Answer

Positive LTFTs mean the ECU is adding fuel to correct a lean condition, commonly caused by unmetered air entering through a vacuum leak.

Question 5

What is the purpose of a fuel pressure regulator in a return-style fuel system?

Accepted Answer

To maintain a constant pressure differential between fuel rail and intake manifold

Answer

A manifold-referenced fuel pressure regulator keeps the pressure drop across injectors constant regardless of boost or vacuum, ensuring accurate fuel delivery.

Car Tuning Practice Test

Car Tuning Practice Test

Car Tuning Fuel and Ignition Management 2