Fuel and Emission Systems Flashcards

What is the purpose of the fuel rail in a multi-port fuel injection system?

Answer: To distribute fuel at equal pressure to all fuel injectors simultaneously

The fuel rail is a manifold that receives pressurized fuel from the supply line and distributes it evenly to all fuel injectors, ensuring consistent pressure and flow to each cylinder.

How does the ECM determine the base fuel injection pulse width?

Answer: From the mass airflow or manifold absolute pressure sensor data combined with engine RPM

The ECM calculates base injector pulse width primarily from engine load (MAF or MAP sensor) and engine speed (RPM from the CKP sensor), then modifies it with corrections from coolant temperature, intake air temperature, and O2 sensors.

A vehicle has a P0420 code (catalyst system efficiency below threshold, bank 1). What is the most common cause?

Answer: A deteriorated catalytic converter that can no longer efficiently convert emissions

P0420 indicates the downstream O2 sensor signal closely mirrors the upstream sensor, meaning the catalytic converter is no longer storing and releasing oxygen effectively. The converter's catalyst material has deteriorated.

What is the effect of a stuck-open fuel injector on engine operation?

Answer: The affected cylinder will run excessively rich, causing misfire, spark plug fouling, and possible catalytic converter damage

A stuck-open injector continuously delivers fuel to its cylinder, creating an extremely rich condition that causes misfires, fouls the spark plug, washes oil from the cylinder walls, and sends raw fuel to the catalytic converter.

What does the manifold absolute pressure (MAP) sensor measure?

Answer: The pressure inside the intake manifold, which the ECM uses to calculate engine load

The MAP sensor measures the absolute pressure in the intake manifold. The ECM compares this to barometric pressure to determine engine vacuum/load and uses it for fuel delivery and ignition timing calculations.

What causes a diesel particulate filter (DPF) to require regeneration?

Answer: Accumulated soot from combustion that must be burned off to restore exhaust flow

The DPF traps particulate matter (soot) from diesel exhaust. As soot accumulates, it increases back pressure. Regeneration raises exhaust temperatures to approximately 600°C to burn off the trapped soot.