Fuel, Air Induction, and Exhaust Systems Flashcards

A fuel pressure test shows correct pressure at idle but drops significantly under full throttle acceleration. This indicates:

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.

A technician performs a fuel injector balance test. One injector causes a smaller pressure drop than the others. This means that injector is:

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.

A vacuum-controlled fuel pressure regulator is removed and inspected. Fuel is found in the vacuum port. This indicates:

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.

An engine equipped with port fuel injection has a rough idle that improves when the air filter is removed. This MOST likely indicates:

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.

What is the purpose of the exhaust back-pressure test?

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.

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:

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.