Fuel Systems Flashcards
7 cards from real ASE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Fuel Systems flashcards as text
Long-term fuel trim reads +20% at idle but drops near 0% at 2,500 rpm. What is the most likely cause?
Answer: Vacuum leak
Unmetered air from a vacuum leak has the biggest effect at idle and becomes small as airflow rises.
On a mechanical returnless fuel system, where is the fuel pressure regulator usually located?
Answer: In the fuel tank pump module
Returnless systems regulate pressure in the tank so no return line from the engine is needed.
Fuel pressure leaks down quickly after key-off, but holds when the return line is pinched. What is the cause?
Answer: Leaking fuel pressure regulator
If pinching the return line stops the leak-down, fuel is escaping past the regulator into the return line.
During an injector balance test, one injector causes a much smaller pressure drop than the others. What does this indicate?
Answer: The injector is restricted or clogged
A smaller pressure drop means less fuel flowed through that injector during the same pulse.
A fuel pump current waveform has an even pattern, but the amperage is well above spec. What is the most likely cause?
Answer: Restriction in the fuel line or a binding pump
Higher current shows the pump motor is working harder against a restriction or mechanical drag.
Raw fuel is found in the vacuum hose of a return-type fuel pressure regulator. What is the diagnosis?
Answer: Ruptured regulator diaphragm
A ruptured diaphragm lets fuel pass into the vacuum side and get pulled into the intake.
Why is a fuel volume test done in addition to a pressure test?
Answer: A pump can make enough pressure but not enough flow under load
Static pressure can look normal even when the pump cannot supply enough flow at high demand.