ASE4 Fuel, Air Induction, and Exhaust Systems 3

Question 1

A fuel trim diagnostic shows STFT (short-term fuel trim) swinging widely between +25% and -25%. This most likely indicates:

Accepted Answer

A slow-responding oxygen sensor

Answer

A stuck-open EGR valve

Answer

Normal closed-loop fuel control

Answer

A failing catalytic converter

Question 2

A scan tool shows both bank LTFT values at +18%. The MOST likely cause is:

Accepted Answer

A large vacuum leak affecting the entire engine

Answer

A leaking fuel injector on one bank

Answer

A faulty oxygen sensor on Bank 1

Answer

A restricted exhaust on Bank 2

Question 3

A returnless fuel system maintains fuel pressure without a return line to the tank. The pressure regulator in this system is located:

Accepted Answer

Inside the fuel tank on the pump module

Answer

At the fuel rail on the engine

Answer

In the fuel filter housing

Answer

At the intake manifold

Question 4

A catalytic converter efficiency code (P0420) is set. Before replacing the converter, the technician should first:

Accepted Answer

Check for misfires, oil burning, or coolant contamination that could have damaged the converter

Answer

Replace both oxygen sensors

Answer

Perform a back-pressure test only

Answer

Replace the converter and retest

Question 5

A cold engine starts and idles but stalls when the throttle is opened. Fuel pressure is normal. The MOST likely cause is:

Accepted Answer

A dirty or failed mass airflow sensor

Answer

A clogged air filter

Answer

Low fuel pump volume

Answer

A stuck-closed EGR valve

Question 6

An engine equipped with GDI (Gasoline Direct Injection) commonly develops carbon deposits on intake valves because:

Accepted Answer

Fuel is injected directly into the cylinder and does not wash the intake valves

Answer

The high injection pressure burns more carbon

Answer

The air/fuel mixture is leaner than port injection systems

Answer

GDI systems lack PCV systems