310S Fuel and Emission Systems 2 — Questions and Answers
Question 1: A fuel pressure test shows lower-than-specified pressure that increases when the return line is pinched. What is the most likely cause?
- A clogged fuel filter
- A faulty fuel pressure regulator allowing excessive fuel return (Correct answer)
- A weak fuel pump
- Leaking fuel injectors
Correct answer: A faulty fuel pressure regulator allowing excessive fuel return
If fuel pressure increases when the return line is restricted, the pump is capable of producing adequate pressure but the regulator is allowing too much fuel to return to the tank.
Question 2: What is the purpose of the secondary air injection (AIR) system?
- To increase combustion chamber air for more power
- To inject fresh air into the exhaust stream to help oxidize HC and CO during cold start (Correct answer)
- To cool the catalytic converter during heavy load
- To pressurize the fuel tank for better fuel delivery
Correct answer: To inject fresh air into the exhaust stream to help oxidize HC and CO during cold start
The AIR system pumps ambient air into the exhaust manifold or catalytic converter during cold start when the engine runs rich, providing oxygen to help oxidize unburned hydrocarbons and carbon monoxide.
Question 3: A technician observes a downstream oxygen sensor signal that is flat at approximately 0.45 volts. What does this indicate?
- A faulty downstream oxygen sensor
- The catalytic converter is functioning efficiently (Correct answer)
- The engine is running extremely rich
- The sensor heater circuit has failed
Correct answer: The catalytic converter is functioning efficiently
A properly functioning catalytic converter stores and releases oxygen, smoothing out the exhaust gas composition. The downstream O2 sensor should show a relatively steady voltage near 0.45V, indicating efficient conversion.
Question 4: What component in a GDI (Gasoline Direct Injection) system creates the high fuel pressure needed for direct injection?
- The in-tank electric fuel pump alone
- A camshaft-driven high-pressure mechanical fuel pump (Correct answer)
- The fuel pressure regulator
- The fuel injectors themselves
Correct answer: A camshaft-driven high-pressure mechanical fuel pump
GDI systems require extremely high fuel pressure (2,000–3,000+ psi) to inject fuel directly into the combustion chamber. A camshaft-driven mechanical pump boosts pressure from the low-pressure electric pump.
Question 5: What causes carbon buildup on the intake valves of GDI engines?
- Using low-octane fuel
- The absence of fuel washing over the intake valves, allowing oil vapour deposits to accumulate (Correct answer)
- Excessive fuel pressure from the high-pressure pump
- A malfunctioning PCV valve only
Correct answer: The absence of fuel washing over the intake valves, allowing oil vapour deposits to accumulate
In port fuel injection, fuel sprayed on the intake valves acts as a detergent. In GDI, fuel is injected directly into the cylinder, so crankcase oil vapours and EGR soot deposit on the valves without being washed away.
Question 6: What does an EVAP system large leak detected code (P0455) indicate?
- A leaking fuel injector
- A significant leak in the fuel vapour containment system such as a loose or missing gas cap (Correct answer)
- A plugged charcoal canister
- A faulty fuel tank pressure sensor
Correct answer: A significant leak in the fuel vapour containment system such as a loose or missing gas cap
P0455 indicates the ECM detected a large leak during EVAP system self-test. The most common cause is a loose, damaged, or missing fuel cap, though it can also indicate a disconnected or cracked EVAP hose.
310S Fuel and Emission Systems 2
A fuel pressure test shows lower-than-specified pressure that increases when the return line is pinched.
What is the most likely cause?