Question 1

The throttle body of a port fuel injected engine may include any of the following components EXCEPT:

Accepted Answer

The oxygen sensor is not located in the throttle body; it is typically found in the exhaust system to measure the amount of oxygen in the exhaust gases for optimal engine performance and emissions control.

Question 2

While discussing PFI systems, Technician A says the PCM provides the proper air/fuel ratio by controlling the fuel pressure. Technician B says the PCM provides the proper air/fuel ratio by controlling the injector pulse width. Who is correct?

Accepted Answer

Technician B is correct because in Port Fuel Injection (PFI) systems, the PCM (Powertrain Control Module) controls the air/fuel ratio by adjusting the injector pulse width, which is the amount of time the fuel injector is open and thus how much fuel is injected into the engine. The fuel pressure in these systems is typically constant, and it's the duration of the injector opening that is varied to control the fuel delivery.

Question 3

An O-ring at the base of a fuel injector ______.

Accepted Answer

O-rings at the base of fuel injectors serve multiple purposes: they seal the injector to its mounting position, provide thermal insulation to prevent vapor bubble formation, and dampen vibrations that could be harmful.

Question 4

Fuel injector firing is being discussed. Technician A says SFI systems control each injector separately so that it fires just before the intake valve opens. Technician B says sequential injector firing is more accurate than multiport systems. Who is correct?

Accepted Answer

Both statements are correct. SFI (Sequential Fuel Injection) systems do control each injector separately, allowing for precise timing of fuel delivery just before the intake valve opens. This makes sequential injector firing more accurate than multiport systems, where injectors may fire in groups rather than individually.

Question 5

Typical fuel injector pulse widths range from _____ to _____ milliseconds.

Accepted Answer

Typical fuel injector pulse widths range from 1 to 10 milliseconds, allowing precise control of fuel delivery to the engine.

Question 6

Technician A says pulsation dampers reduce the pressure pulsations caused by the rapid opening and closing of the fuel injectors. Technician B says the damper helps to reduce fuel noise and maintains pressure during engine cooldown. Who is correct?

Accepted Answer

Both technicians are correct. Technician A is correct in stating that pulsation dampers reduce pressure pulsations caused by the rapid opening and closing of fuel injectors, which helps in maintaining a steady flow of fuel. Technician B is correct in stating that these dampers help reduce fuel system noise and can help maintain pressure in the system during engine cooldown, contributing to smoother engine operation and potentially easier starts.

Question 7

MAP output is the same as what is measured on a vacuum gauge. When intake vacuum is high, MAP voltage is high.

Accepted Answer

MAP (Manifold Absolute Pressure) sensor output is inversely related to intake vacuum; when intake vacuum is high, MAP voltage is typically low, as the sensor measures absolute pressure, which decreases as vacuum increases.

Question 8

Technician A says the vacuum hose on the fuel pressure regulator of a PFI system is connected to the intake manifold. Technician B says the fuel pressure regulator of a TBI injection system doesn't need a vacuum hose to regulate pressure because the injectors are located above the throttle plate where the air pressure is constant. Who is correct?

Accepted Answer

Technician A is correct because in a Port Fuel Injection (PFI) system, the fuel pressure regulator's vacuum hose is indeed connected to the intake manifold to adjust fuel pressure based on engine load and vacuum. Technician B is also correct because in a Throttle Body Injection (TBI) system, the fuel pressure regulator doesn't require a vacuum hose since the fuel injectors are located above the throttle plate, where the pressure remains relatively constant regardless of engine load.

Question 9

Technician A says piezoelectric injectors rely on stacked crystals that expand when a voltage is applied. Technician B says piezoelectric injectors are slower acting than solenoid-type injectors. Who is correct?

Accepted Answer

Technician A is correct because piezoelectric injectors do indeed use stacked crystals that expand when a voltage is applied, which changes the injector needle position to allow fuel injection. Technician B is incorrect because piezoelectric injectors are actually faster acting than solenoid-type injectors, offering more precise control over fuel injection.

Question 10

Fuel injectors may be controlled ______.

Accepted Answer

Fuel injectors can be controlled in various ways depending on the engine's design and the vehicle's requirements. They can be controlled in pairs or groups, all at once, or sequentially, allowing for precise fuel delivery and optimal engine performance.

Question 11

Technician A says an air/fuel ratio sensor responds to minor changes in the air/fuel mixture. Technician B says that when an air/fuel ratio sensor is used on an OBD-II vehicle, both the upstream and downstream sensors must be air/fuel ratio type sensors. Who is correct?

Accepted Answer

Technician A is correct because an air/fuel ratio sensor, also known as a wideband oxygen sensor, is designed to precisely measure the air/fuel mixture in real-time, allowing for minor adjustments to be made for optimal engine performance. Technician B is incorrect because it is not necessary for both the upstream and downstream sensors to be air/fuel ratio type sensors. The downstream sensor, often a traditional oxygen sensor, primarily monitors the efficiency of the catalytic converter rather than the air/fuel mixture.

Question 12

Which of the following is NOT representative of sequential fuel injection systems?

Accepted Answer

Sequential fuel injection systems operate by delivering fuel directly to each cylinder in a sequence that matches the engine's firing order, rather than all injectors receiving the same command simultaneously. This allows for more precise fuel control and efficiency.

Question 13

Technician A says in a returnless fuel system, the pressure regulator is mounted on the fuel rail. Technician B says in a returnless fuel system the pressure regulator, fuel sender, and pump assembly are combined in one unit inside the fuel tank. Who is correct?

Accepted Answer

In a returnless fuel system, the pressure regulator is typically integrated with the fuel pump assembly inside the fuel tank, not mounted on the fuel rail. This design reduces the need for fuel to be returned to the tank from the engine, improving efficiency.

Question 14

While discussing central port injection (CPI), Technician A says the poppet nozzles are opened by the computer. Technician B says the poppet nozzles are opened by fuel pressure. Who is correct?

Accepted Answer

The poppet nozzles in a central port injection system are opened by fuel pressure, not directly by the computer.

Question 15

Technician A says a throttle body may house one fuel injector. Technician B says a throttle body may house two fuel injectors. Who is correct?

Accepted Answer

Throttle bodies can be designed with one or multiple fuel injectors depending on the engine's requirements and design. Therefore, both Technician A and Technician B are correct.

Question 16

Technician A says throttle-by-wire systems (ETC)eliminate the need for a cruise control actuator. Technician B says ETC also allows the PCM to be more effective when limiting engine and vehicle speeds. Who is correct?

Accepted Answer

Both statements are correct. Throttle-by-wire systems eliminate the need for a mechanical connection between the accelerator pedal and the throttle, allowing for the integration of cruise control functionality without a separate actuator. They also enable the Powertrain Control Module (PCM) to more effectively manage engine and vehicle speeds by electronically controlling the throttle.

Question 17

Technician A says TBI systems use top fuel-feeding injectors. Technician B says PFI systems use bottom fuel-feeding injectors. Who is correct?

Accepted Answer

TBI (Throttle Body Injection) systems typically use injectors mounted in the throttle body that spray fuel above the throttle plates, not necessarily "top feeding" in the context implied. PFI (Port Fuel Injection) systems have injectors that spray fuel directly into the intake port of each cylinder, not necessarily "bottom feeding." The descriptions provided don't accurately represent how these systems feed fuel, leading to the conclusion that neither technician is correct.

Question 18

Technician A says the computer uses the TP sensor and ECT sensor signals to determine the amount of air entering the engine in a speed-density system. Technician B says the computer uses the TP sensor and oxygen sensor signals to determine the amount of air entering the engine in a speed-density system. Who is correct?

Accepted Answer

The answer of Technician A says the computer uses the...

Question 19

In closed loop, the PCM adjusts the pulse width according to inputs from a variety of sensors, but primarily the _____.

Accepted Answer

In closed loop operation, the Powertrain Control Module (PCM) primarily adjusts the fuel injector pulse width based on feedback from the oxygen sensor(s) to maintain the optimal air-fuel ratio. This ensures efficient combustion and minimizes emissions.

Question 20

While cranking a fuel injected engine and holding the accelerator to the wide-open throttle position, the air/fuel mixture will be ______.

Accepted Answer

Holding the accelerator to the wide-open throttle position during cranking in a fuel-injected engine activates a clear flood mode, which reduces the amount of fuel injected, resulting in a lean air/fuel mixture.

Quiz 30: Electronic Fuel Injection