Question 1

Technician A says that vehicles with electronic returnless fuel systems use pulse width modulation to power the fuel pump and maintain fuel pressure. Technician B says that the electronic returnless fuel system uses a power transistor to control the fuel pump. Which technician is correct?

A)Technician A only
B)Technician B only
C)Both technicians A and B
D)Neither technician A nor B

Both technicians A and B

Accepted Answer

Both technicians are correct. Electronic returnless fuel systems use pulse width modulation (PWM) to control the speed of the fuel pump, which is a method of varying the amount of time (width) the fuel pump is powered within a given time frame (pulse). This system also utilizes a power transistor (often part of the fuel pump control module) to regulate the current to the fuel pump, achieving the desired fuel pressure without returning excess fuel to the tank.

Question 2

One type of injection system does that does not hold pressure when turned off is called a non-checking system. This is found on ________.&#10;A)Multiport injection systems&#10;B)All TBI systems&#10;C)Some General Motors TBI systems&#10;D)None of these

Accepted Answer

Some General Motors Throttle Body Injection (TBI) systems are designed as non-checking systems, meaning they do not maintain fuel pressure after the ignition is turned off. This contrasts with other fuel injection systems that are designed to hold pressure when not in operation.

Question 3

Which type of port fuel injection fires all the injectors at the same time, once per crankshaft revolution?&#10;A)Throttle body injection&#10;B)Simultaneous double fired&#10;C)Gang double fired&#10;D)Sequential fired

Accepted Answer

Simultaneous double fired injection fires all the injectors at the same time, once per crankshaft revolution.

Question 4

Dampeners are used on some fuel rails to ________.&#10;A)Trap dirt and keep it away from the injectors&#10;B)Reduce (decrease) the fuel pressure in the rail&#10;C)Increase the fuel pressure in the rail&#10;D)Reduce noise

Accepted Answer

Dampeners on fuel rails are primarily used to reduce noise, particularly the noise generated by the rapid opening and closing of the fuel injectors and the pulsation of fuel within the rail.

Question 5

Technician A says that an idle air control valve controls the airflow past closed throttle plates. Technician B says that the idle air control valve is usually controlled by a stepper motor. Which technician is correct?

A)Technician A only
B)Technician B only
C)Both technicians A and B
D)Neither technician A nor B

Accepted Answer

Both statements are correct. The idle air control (IAC) valve does control airflow past the closed throttle plates to regulate engine idle speed, and it is commonly operated by a stepper motor which precisely controls its position.

Deck 78: Fuel-Injection Components and Operation