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
What is the typical resistance of a high-impedance (saturated-switch) port fuel injector?
Answer: 12–16 ohms
High-impedance injectors usually measure about 12–16 ohms, while low-impedance (peak-and-hold) injectors measure about 2–5 ohms.
An injector voltage waveform shows a much smaller inductive kick than the other injectors. What is the most likely cause?
Answer: Shorted turns in the injector winding
Shorted windings lower the coil's inductance, so the voltage spike when it shuts off is smaller.
A noid light flashes normally on a cylinder, but that injector does not spray fuel. What is the likely cause?
Answer: The injector is mechanically stuck or clogged
A flashing noid light proves the electrical signal is there, so the fault is inside the injector itself.
On most port fuel injection systems, how does the PCM turn on an injector?
Answer: By grounding the injector circuit
Injectors get battery voltage from a relay, and the PCM's low-side driver completes the ground.
The upstream oxygen sensor reads a steady 0.1 V at warm cruise. How will the PCM respond in closed loop?
Answer: Increase injector pulse width
A steady low O2 voltage shows a lean condition, so the PCM adds fuel by lengthening the pulse width.
Which symptom combination best points to a leaking (dripping) injector?
Answer: Hard hot start, rich condition, and fuel pressure leak-down
A dripping injector floods the cylinder during a hot soak and lets rail pressure bleed off.
The fuel pump primes for 2 seconds at key-on but does not run while cranking, and the engine won't start. What is the most likely cause?
Answer: A faulty crankshaft position sensor signal
The PCM keeps the pump running only when it sees an engine speed signal from the CKP sensor.