Car Tuning Fuel and Ignition Management Questions and Answers

Question 1

When tuning a turbocharged engine under high boost, what is the primary reason for targeting a richer air-fuel ratio (e.g., 11.5:1) compared to the stoichiometric ratio (14.7:1)?

Accepted Answer

To prevent detonation and cool the combustion chamber.

Answer

Under high boost, cylinder pressures and temperatures increase significantly, raising the risk of detonation (engine knock). Running a richer air-fuel ratio introduces excess fuel that doesn't fully combust but instead evaporates, absorbing heat and cooling the combustion chamber. This cooling effect helps suppress detonation, protecting the engine from damage.

Question 2

A tuner is adjusting ignition timing on a naturally aspirated engine. As engine RPM increases at a constant load, how should the ignition timing generally be adjusted to maintain optimal power?

Accepted Answer

It should be advanced.

Answer

As engine RPM increases, the piston travels faster, reducing the time available for the air-fuel mixture to burn completely. To ensure that peak cylinder pressure occurs at the optimal point after top dead center (TDC) for maximum force on the piston, the spark must be initiated earlier in the compression stroke. This is known as advancing the ignition timing.

Question 3

A customer's vehicle is being tuned using a speed-density system. Which of the following tables is most critical for the ECU to accurately calculate the necessary amount of fuel to inject?

Accepted Answer

Volumetric Efficiency (VE) table.

Answer

In a speed-density system, the ECU calculates the mass of air entering the engine based on data from the Manifold Absolute Pressure (MAP) sensor, intake air temperature sensor, and engine speed (RPM). The Volumetric Efficiency (VE) table is a crucial map that tells the ECU how efficiently the engine is breathing (pumping air) at various RPM and load points. An accurate VE table is fundamental for the ECU to calculate the correct fuel mass to achieve the target air-fuel ratio.

Question 4

During a tuning session, the knock sensor detects detonation. Which of the following is the most appropriate immediate action for the Engine Control Unit (ECU) to take?

Accepted Answer

Retard ignition timing.

Answer

The primary function of a knock sensor is to detect the high-frequency vibrations caused by detonation. When the ECU receives this signal, its immediate protective response is to retard the ignition timing. Firing the spark plug later in the compression stroke reduces cylinder pressure and temperature, which helps to stop the uncontrolled combustion event and protect the engine from damage.

Question 5

What is the primary function of adjusting 'Ignition Dwell Time' in an engine's tune?

Accepted Answer

To ensure the ignition coil has sufficient time to charge for a strong spark.

Answer

Ignition dwell time is the duration that current flows through the ignition coil's primary winding to build up a magnetic field. This stored energy is then released as a high-voltage spark when the current is cut. Setting the correct dwell time is crucial; too little dwell results in a weak spark and potential misfires, while too much can overheat and damage the coil.

Car Tuning Practice Test

Car Tuning Practice Test

Car Tuning Fuel and Ignition Management Questions and Answers