Wrap-Up

Ready for Review

• Gasoline direct injection (GDI) injects fuel directly into the combustion chamber.
• The compression ratio is much higher on a GDI engine than it is on a conventional engine.
• The pistons are different on a GDI engine than on a conventional engine because GDI directs the fuel flow toward the spark plug.
• The injectors operate on a higher voltage, between 48 and 65 volts.
• The mechanical fuel regulator is located on the fuel pump sender in the fuel tank. This is the low-pressure side of the system.
• The low-pressure side feeds the high-pressure side so that it can make enough pressure to atomize the fuel when it sprays out of the injector.
• The powertrain control module (PCM) uses the high-pressure fuel sensor to determine how much fuel pressure is needed to operate the engine.
• The homogenous mode is used when the engine is in a state of steady engine operation.
• The stratified mode is used to inject fuel just before top dead center (TDC) to allow for very lean operation.
• A dual injection system is used to help with lowering emissions from the GDI engine.
• Dual injection uses port fuel for lower-end operation because it is more efficient than GDI at this level.
• As the rpm are increased, the GDI takes over when it is more efficient.
• GDI injection creates more engine noise than a conventional engine because of the fuel-injection pulses.
• Regular carbon cleaning may be necessary on certain applications, to prevent engine valve issues.

Key Terms

gasoline direct injection (GDI)  A fuel-injection system in which fuel is sprayed directly into the combustion chamber.

high-pressure fuel sensor  An electrical transducer on the high-pressure injection pump or the high-pressure fuel rail that gives feedback to the PCM to make fuel-injection decisions.

high-pressure injection pump  A mechanical fuel pump that takes a low-pressure fuel charge and increases the pressure up to 3,000 psi (207 bar).

homogeneous operation mode  A mode during which the PCM injects the fuel on the intake stroke to allow the air-fuel mixture to be evenly dispersed throughout the combustion chamber.

Otto four-stroke cycle  A four-stroke cycle that includes intake, compression, combustion, and exhaust. It is the most commonly used cycle on an ICE.

stratified charge mode  A layering of a lean air-fuel mixture in the combustion chamber. It is used when the fuel injector and piston head place fuel near the spark plug but not the surrounding space.

top dead center (TDC)  The very top of the stroke of the piston in a cylinder, where the piston cannot move any higher.

Review Questions

1. The GDI high-side fuel-injection pressures go as high as _________.
   • 25 psi (172 kPa)
   • 5,000 psi (34,500 kPa)
   • 150 psi (1,034 kPa)
   • 60 psi (414 kPa)
2. The fuel injector is located in which part of the engine on a GDI application?
   • Combustion chamber.
   • Intake manifold.
   • Valve spring.
   • Throttle body.
3. How is the high-pressure injection pump powered?
   • It’s an electrical pump.
   • It’s a mechanical pump driven off of the camshaft.
   • It’s belt driven off of the balancer.
   • It’s driven off of the timing belt.
4. Choose the correct statement.
   • GDI engines are not very efficient and can cause more emissions than a standard internal combustion engine.
   • Dual injection systems are used only to increase complexity so that only dealer technicians can work on these types of vehicles.
   • The high-pressure fuel system can increase the low-side fuel pressure to over 2,000 psi (138 bar).
   • The PCM controls only the high-pressure injection pump.
5. A dual fuel-injection system on a GDI engine is used to _______________________.
   • decrease the need for filling the vehicle with fuel
   • do nothing other than to sell more components
   • increase the power of the engine by injecting more fuel into the cylinder
   • help to decrease the need for regular maintenance on the system and decrease particulate matter (PM) created
6. The high-pressure fuel sensor is used _______________.
   • to send feedback to the PCM to help control fuel-injector timing
   • to control injector-opening timing so that the injector stays on longer than normal
   • for easy start-up and shutdown
   • to turn on the ignition system
7. A mechanical regulator uses what type of control to release built-up pressure within the low-side fuel system?
   • Electrical.
   • Spring pressure.
   • Vacuum.
   • PCM.
8. The injection events can be only a singular event.
   • True.
   • False.
9. A major issue with the intake valves on a GDI engine is the development of what?
   • An injector hitting the valve, which could cause a drivability issue.
   • Broken valves, because of the increased lift.
   • Carbon buildup, which may cause a valve not to seat close.
   • Hot spots from the fuel being injected on it.
10. In a dual injection fuel system, the PCM uses both types of injectors to reduce which type of engine output?
    • Exhaust.
    • Emissions.
    • Heat.
    • Power.

ASE Technician A/Technician B–Style Questions

1. Technician A says the GDI injector uses the water jacket that it is housed in to help cool it form the combustion chamber temperatures. Technician B says a GDI engine has only one mode of operation. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
2. Technician A says that a modern GDI engine creates noise based on the mechanical fuel pump pulses as it creates pressure. Technician B says homogenous injection mode injects fuel during the intake event, which allows it to mix more thoroughly with the air in the combustion chamber. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
3. Technician A says the piston design depends on where the injector is located in the cylinder head and in what direction it is pointing at the top of the piston. Technician B says the high-pressure injection pump is run off of a belt. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
4. Technician A says that GDI engine intake valves are cleaner than those of a port fuel-injection engine. Technician B says the high-pressure fuel sensor allows the PCM to determine whether it needs to command the injection pump on longer to create more pressure. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
5. Technician A says when the engine is in stratified mode, it is very lean and can create a very hot condition. Technician B says GDI injectors operate on a 12-volt power scale. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
6. Technician A says timing the injection pump to the engine will allow for the pressure event to happen when the injector is open. Technician B says regular maintenance of a GDI engine may require top-end engine cleaning. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
7. Technician A says an electronic regulator is controlled by the PCM to maintain fuel pressure in the high-pressure fuel rail. Technician B says a dual injector system uses the port fuel injectors to help reduce PM. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
8. Technician A says the mechanical injection pump is controlled on its own (without any outside control). Technician B says the compression ratio on a GDI engine is between 8:1 and 10:1. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
9. Technician A says the high-pressure injection pump is operated by the camshaft. Technician B says the mechanical components of the engine are the same as those of a conventional ICE. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
10. Technician A says that in a conventional port fuel-injection engine, the injector would wash the backside of the intake valve. Technician B says carbon can build up on the intake valves over time and that they therefore should be cleaned. Who is correct?
    • Technician A
    • Technician B
    • Both A and B
    • Neither A nor B