310S Fuel and Emission Systems 4 — Questions and Answers
Question 1: What is the purpose of the fuel rail in a multi-port fuel injection system?
- To regulate fuel pressure to each injector
- To distribute fuel at equal pressure to all fuel injectors simultaneously (Correct answer)
- To return excess fuel to the tank
- To filter fuel before it reaches the injectors
Correct 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.
Question 2: How does the ECM determine the base fuel injection pulse width?
- From the throttle position sensor signal alone
- From the mass airflow or manifold absolute pressure sensor data combined with engine RPM (Correct answer)
- From the oxygen sensor feedback exclusively
- From the coolant temperature sensor signal only
Correct 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.
Question 3: A vehicle has a P0420 code (catalyst system efficiency below threshold, bank 1). What is the most common cause?
- A faulty upstream oxygen sensor
- A deteriorated catalytic converter that can no longer efficiently convert emissions (Correct answer)
- An exhaust manifold leak
- A clogged fuel filter
Correct 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.
Question 4: What is the effect of a stuck-open fuel injector on engine operation?
- The affected cylinder will misfire due to a lean condition
- The affected cylinder will run excessively rich, causing misfire, spark plug fouling, and possible catalytic converter damage (Correct answer)
- The engine will not start
- Fuel pressure will increase across all cylinders
Correct 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.
Question 5: What does the manifold absolute pressure (MAP) sensor measure?
- Atmospheric pressure outside the vehicle
- The pressure inside the intake manifold, which the ECM uses to calculate engine load (Correct answer)
- The pressure in the fuel rail
- The back pressure in the exhaust system
Correct 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.
Question 6: What causes a diesel particulate filter (DPF) to require regeneration?
- Excessive fuel consumption
- Accumulated soot from combustion that must be burned off to restore exhaust flow (Correct answer)
- Water contamination in the diesel fuel
- A clogged fuel filter restricting fuel flow
Correct 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.
310S Fuel and Emission Systems 4
What is the purpose of the fuel rail in a multi-port fuel injection system?