ASE4 Fuel, Air Induction, and Exhaust Systems 1 — Questions and Answers
Question 1: A fuel pressure test shows correct pressure at idle but drops significantly under full throttle acceleration. This indicates:
- A restricted fuel filter or weak fuel pump (Correct answer)
- A leaking fuel pressure regulator
- A faulty MAP sensor
- Stuck-open fuel injectors
Correct answer: A restricted fuel filter or weak fuel pump
Fuel pressure that drops under high-demand acceleration indicates the pump or filter cannot maintain adequate flow.
Question 2: A technician performs a fuel injector balance test. One injector causes a smaller pressure drop than the others. This means that injector is:
- Flowing too much fuel (stuck open)
- Flowing too little fuel (clogged or weak) (Correct answer)
- Working normally
- Leaking when the engine is off
Correct answer: Flowing too little fuel (clogged or weak)
A smaller pressure drop during an injector balance test means the injector delivered less fuel, indicating a restriction or weak coil.
Question 3: A vacuum-controlled fuel pressure regulator is removed and inspected. Fuel is found in the vacuum port. This indicates:
- The regulator is operating normally under boost
- The regulator diaphragm has failed, allowing fuel into the vacuum system (Correct answer)
- The fuel pressure is too high
- The intake manifold has a vacuum leak
Correct answer: The regulator diaphragm has failed, allowing fuel into the vacuum system
Fuel in the vacuum port of a pressure regulator indicates a ruptured diaphragm, allowing fuel to enter the intake vacuum line.
Question 4: An engine equipped with port fuel injection has a rough idle that improves when the air filter is removed. This MOST likely indicates:
- A rich air/fuel mixture
- A severely restricted air filter causing a lean condition (Correct answer)
- A faulty MAF sensor
- A vacuum leak past the throttle plate
Correct answer: A severely restricted air filter causing a lean condition
Idle improvement with the air filter removed points to a severely restricted filter that was choking airflow to the engine.
Question 5: What is the purpose of the exhaust back-pressure test?
- To measure combustion efficiency
- To detect a restricted catalytic converter or exhaust system (Correct answer)
- To test oxygen sensor response time
- To measure EGR valve flow
Correct answer: To detect a restricted catalytic converter or exhaust system
Back-pressure testing identifies exhaust restriction — typically a plugged catalytic converter — that can cause a loss of power.
Question 6: A technician finds fuel pressure holds for 30 seconds after the engine is shut off but then bleeds down slowly over several minutes. This MOST likely indicates:
- A faulty check valve in the fuel pump
- Normal pressure bleed-down for a returnless system
- A leaking fuel injector (Correct answer)
- A failing fuel pressure regulator
Correct answer: A leaking fuel injector
Slow bleed-down of residual fuel pressure after shutdown typically indicates a leaking fuel injector allowing fuel to drip into the intake.
ASE4 Fuel, Air Induction, and Exhaust Systems 1
A fuel pressure test shows correct pressure at idle but drops significantly under full throttle acceleration.
This indicates: