Question 1

A scan tool is used in diagnosis to observe ________.&#10;A)Long term fuel trim&#10;B)Idle air counts&#10;C)Short term fuel trim&#10;D)All of these

Accepted Answer

A scan tool can be used to observe long term fuel trim, idle air counts, and short term fuel trim, making all the options correct.

Question 2

Technician A says that the fuel system should be diagnosed first in a no-start condition. Technician B says that the ignition system trigger device is used to synchronize fuel injection. 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

In a no-start condition, diagnosing the fuel system is a common and logical first step, as fuel delivery issues are a common cause of such problems, making Technician A correct. Technician B is also correct because the ignition system's trigger device (such as a crankshaft or camshaft position sensor) is indeed used to synchronize fuel injection with the engine's ignition cycle.

Question 3

The following statements are all correct EXCEPT ________.&#10;A)Fuel systems that have never been cleaned may have developed wax deposits as well as carbon&#10;B)On engines operating very poorly, the PCM should be relearned after fuel system cleaning&#10;C)The fuel rail and pressure regulator should be cleaned as well as fuel injectors&#10;D)Relearning the PCM should never be attempted

Accepted Answer

Relearning the PCM (Powertrain Control Module) is a common procedure after certain repairs or maintenance tasks, such as fuel system cleaning, to ensure the engine operates efficiently. Saying it should never be attempted is incorrect.

Question 4

When looking at a solenoid with an oscilloscope, what event often follows applying or removing power from the coil windings?&#10;A)Decreased resistance&#10;B)Voltage drop&#10;C)Diode ripple&#10;D)Voltage spike

Accepted Answer

When power is applied or removed from a solenoid's coil windings, the changing magnetic field can induce a voltage spike. This phenomenon is due to electromagnetic induction, where a change in magnetic flux through a coil generates an electromotive force (EMF) across the coil.

Question 5

All of the following statements are correct EXCEPT ________.&#10;A)Fuel injectors on a gang fire system are wired in series&#10;B)Lower than specified injector resistance means the injector is shorted&#10;C)The resistance of a group of injectors that fire at the same time can be tested together&#10;D)None of these

Accepted Answer

Fuel injectors on a gang fire system are typically wired in parallel, not in series. This allows each injector to receive the same voltage and operate simultaneously when the system is activated. Wiring in series would result in a drop in voltage across each injector in the chain, which is not how these systems are designed to function.

Question 6

Which of the following values for IAC count would indicate a vacuum leak on a speed density system?&#10;A)5 or less&#10;B)15&#10;C)30 or more&#10;D)25

Accepted Answer

The answer of Which of the following values for IAC...

Question 7

On a vehicle with a speed density fuel injection system, which of the following is likely to occur with a vacuum leak?&#10;A)Increased MAP sensor voltage&#10;B)Increased calculated load&#10;C)Increased idle speed&#10;D)All of these are correct.

Accepted Answer

A vacuum leak in a speed density fuel injection system can lead to increased MAP (Manifold Absolute Pressure) sensor voltage because the sensor will detect a lower pressure in the intake manifold, interpreting it as more air entering the engine. This, in turn, causes the engine control unit (ECU) to calculate a higher engine load to compensate for the perceived increase in air, leading to adjustments in fuel delivery. Additionally, the vacuum leak can cause an increase in idle speed as the engine tries to stabilize by adjusting the air-fuel mixture to deal with the unmetered air entering through the leak.

Question 8

What test is being performed here?  &#10;A)Injector pressure drop&#10;B)Injector voltage drop&#10;C)Injector temperature&#10;D)Injector resistance

Accepted Answer

The answer of What test is being performed here? ...

Deck 81: Fuel-Injection System Diagnosis and Service