CPT Fuel Systems & Engine Performance Flashcards
6 cards from real CPT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 CPT Fuel Systems & Engine Performance flashcards as text
What does injector duty cycle (IDC) percentage represent, and at what approximate IDC should a CPT technician consider upgrading injectors?
Answer: Percentage of time injectors are open per cycle; upgrade when IDC exceeds 80% to maintain safe headroom
IDC is the percentage of engine cycle time the injector is open; above 80% leaves insufficient headroom for enrichment, requiring larger injectors.
A turbocharged engine with a return-less fuel system shows fuel pressure drop at high boost levels. What modification would a CPT technician recommend first?
Answer: Install a boost-referenced fuel pressure regulator to maintain pressure differential under boost
A boost-referenced FPR increases fuel rail pressure proportionally with boost pressure, maintaining the correct pressure differential across injectors at high boost.
When testing a high-pressure GDI fuel pump, a technician measures fuel pressure at idle that fluctuates rapidly between 500 and 2,500 psi. What is the most likely cause?
Answer: A worn high-pressure pump cam lobe or damaged pump internals causing inconsistent pumping strokes
GDI high-pressure pump pressure should be stable; rapid fluctuation indicates the pump cannot maintain consistent displacement due to internal or cam lobe wear.
Which fuel system component prevents vapor lock in a high-performance fuel system operating in hot conditions?
Answer: An in-tank fuel pump with a return line keeping cool fuel circulating through the rail
A return-type fuel system with an in-tank pump circulates cool fuel continuously, preventing heat soak and vapor lock in the fuel rail.
A performance technician notices that fuel pressure rises above spec when the EVAP purge valve opens at light throttle. What does this indicate?
Answer: The purge valve is introducing fuel vapors that are enriching the mixture, reflected as a fuel pressure increase from reduced injector demand
When EVAP vapors enter the intake, the ECU reduces injector pulse width to compensate, causing fuel pressure to rise as less fuel flows through the rail.
What is the purpose of a fuel accumulator in some return-type fuel systems?
Answer: To dampen fuel pressure pulsations from the pump and maintain rail pressure briefly after shutdown
A fuel accumulator uses a spring-loaded diaphragm to absorb pump pressure pulses and maintain residual rail pressure briefly after the pump stops.