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 part of the throttle body; it is located in the exhaust system to measure the oxygen level in the exhaust gases.

Question 2

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

Technician B is correct. In a returnless fuel system, the pressure regulator, fuel sender, and pump assembly are combined in one unit inside the fuel tank. The pressure regulator is not mounted on the fuel rail.

Question 3

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. The PCM (Powertrain Control Module) provides the proper air/fuel ratio by controlling the injector pulse width, which determines how long the injector stays open during each cycle. It does not control fuel pressure in a PFI (Port Fuel Injection) system.

Question 4

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

Accepted Answer

Typical fuel injector pulse widths range from 1 millisecond to 10 milliseconds.

Question 5

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. Pulsation dampers are designed to reduce pressure pulsations caused by the rapid opening and closing of the fuel injectors, and they also help to reduce fuel noise and maintain pressure during engine cooldown.

Question 6

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

Accepted Answer

An O-ring at the base of a fuel injector seals the injector to its mounting position, provides thermal insulation to prevent the formation of vapor bubbles, and dampens potentially damaging vibrations.

Question 7

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 8

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 9

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

Accepted Answer

The oxygen sensor provides the most important input for the PCM in closed loop operation, as it allows the PCM to constantly adjust the air/fuel ratio for optimal combustion and emissions control. The other sensors listed are also important, but not as critical in closed loop operation as the oxygen sensor.

Question 10

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

Both technicians are incorrect. TBI (Throttle Body Injection) systems use injectors that spray fuel into the throttle body, which is located on top of the engine. PFI (Port Fuel Injection) systems use injectors that spray fuel into the intake ports, which are located on the bottom of the intake manifold. Neither system uses top or bottom fuel-feeding injectors.

Question 11

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 12

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

Throttle-by-wire systems (ETC) do eliminate the need for a cruise control actuator, as stated by Technician A. Additionally, Technician B is correct in stating that ETC allows the PCM to be more effective in limiting engine and vehicle speeds. Therefore, both technicians are correct.

Question 13

Fuel injectors may be controlled ______.

Accepted Answer

Fuel injectors can be controlled in various ways, including in pairs or groups, all at once, or sequentially, depending on the engine design and control strategy.

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

Technician B is correct. Poppet nozzles in CPI systems are opened by fuel pressure. The computer regulates the fuel pressure to control the fuel flow to the injectors.

Question 15

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.

Question 16

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

Accepted Answer

Sequential fuel injection systems fire each injector individually in sequence, not simultaneously.

Question 17

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 18

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

Technician A is correct in stating that SFI systems control each injector separately to fire just before the intake valve opens. Technician B is also correct in stating that sequential injector firing is more accurate than multiport systems. Therefore, both technicians A and B are correct.

Question 19

Fuel injectors are ______.

Accepted Answer

Fuel injectors can be either top fuel-feeding devices or bottom fuel-feeding devices.

Question 20

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.

Quiz 30: Electronic Fuel Injection