Deck 31: Fuel Injection System Diagnosis and Service

Question 1

Preliminary checks are being discussed. Technician A says to run specific fuel injection tests first. Technician B says most driveability concerns are caused by PCM-related problems. Who is correct?

A) A only
B) B only
C) both A and B
D) neither A nor B

Answer 1

D

Question 2

The engine must be at normal operating temperature before the ECT sensor is tested.

Answer 2

False

Question 3

Static test replacement computers, modules, and computer chips prior to installation.

Answer 3

False

Question 4

Always pressurize the fuel system before disconnecting any fuel system components.

Question 5

The IAC motor cannot be actuated with a scan tool.

Question 6

An exhaust gas analyzer can be used to determine whether an injector is leaking.

Question 7

Never turn on the ignition switch when any fuel system component is disconnected.

Question 8

A good injector makes a rhythmic clicking sound as the injector is energized and de-energized several times each second.

Question 9

The LTFT works to bring the STFT close to a 0 percent correction.

Question 10

IAC motor damage may result if throttle body cleaner is allowed to enter the motor.

Question 11

The engine must be at normal operating temperature before the O₂ sensor is tested.

Question 12

Creating a large vacuum leak will cause the short-term fuel trim (STFT) and long-term fuel trim (LTFT) to decrease.

Question 13

One test of a GM hot film mass airflow meter includes tapping it with a plastic mallet or screwdriver handle.

Question 14

STFT adjustments are temporary and are not stored in the PCM's memory.

Question 15

It is impossible to visually check the spray pattern and volume of port system injectors.

Question 16

Fuel trim is being discussed. Technician A says a + 12.0 percent LTFT value indicates that the system is running 12 percent richer than normal. Technician B says LTFT should constantly change between positive and negative values when the system is running in closed loop. Who is correct?

A) A only
B) B only
C) both A and B
D) neither A nor B

Question 17

Other than inspecting the electrical connections, there are usually no physical checks to mass airflow or manifold absolute pressure sensors.

Question 18

Which of the following sensors is used to modify the engine's air/fuel mixture based on oxygen in the exhaust?

A) O₂ sensor
B) TP sensor
C) MAP sensor
D) MAF sensor

Question 19

If the IAC pintle is extended too far, the motor can be damaged during installation.

Question 20

An oxygen sensor must heat up to approximately _____ before functioning in its closed loop mode.

A) 200°F (93°C)
B) 400°F (204°C)
C) 600°F (316°C)
D) 800°F (427°C)

Question 21

Technician A says an intake manifold vacuum leak may cause a high idle speed. Technician B says a dirty IAC bypass passage will not cause the idle speed to be below specifications. Who is correct?

A) A only
B) B only
C) both A and B
D) neither A nor B

Question 22

Most heated oxygen sensors have _____ wire(s) connected to them.

A) one
B) two
C) three
D) four

Question 23

Which of the following would not cause the fuel pressure to drop to zero immediately after engine shut down?

A) leaking pressure regulator vacuum line
B) leaking fuel pressure regulator
C) leaking fuel pump check valve
D) leaking fuel injector

Question 24

Short-term and long-term fuel trim readings are being discussed. Technician A says a scale of 0 to 255 is used. Technician B says percentage is used. Who is correct?

A) A only
B) B only
C) both A and B
D) neither A nor B

Question 25

Which of the following should be checked before proceeding with specific fuel injection and electronic control testing?

A) vacuum lines
B) PCV system
C) engine coolant level
D) all answers are correct

Question 26

Operation of an O₂ sensor is checked with a(n) _____.

A) ammeter
B) ohmmeter
C) voltmeter
D) all answers are correct

Question 27

Technician A says the IAC counts should change when the A/C compressor is turned on and off. Technician B says if the scan tester indicates zero IAC counts, there may be an open circuit between the PCM and the IAC motor. Who is correct?

A) A only
B) B only
C) both A and B
D) neither A nor B

Question 28

Technician A says higher than normal idle speed may be caused by an air-conditioning switch that is always closed. Technician B says higher than normal idle speed may be caused by a defective engine coolant temperature sensor. Who is correct?

A) A only
B) B only
C) both A and B
D) neither A nor B

Question 29

Which of the following would NOT cause the fuel trim to be out of range?

A) faulty fuel pressure regulator
B) restricted fuel filter
C) faulty mass air flow sensor [MAF]
D) faulty IAC motor [idle air control]

Question 30

Quick tests to a GM hot film mass airflow meter on an engine with idling problems are being performed. Technician A taps on the meter lightly with a plastic mallet. Technician B unplugs the meter. Who is correct?

A) A only
B) B only
C) both A and B
D) neither A nor B

Question 31

Technician A says a rich air/fuel ratio may be caused by low fuel pump pressure. Technician B says a rich air/fuel ratio may be caused by a defective engine coolant temperature sensor. Who is correct?

A) A only
B) B only
C) both A and B
D) neither A nor B

Question 32

A technician is testing a fuel injection system with a scan tool. While the engine is running in closed loop, he loosens a vacuum hose to create a small vacuum leak. Initially the STFT rises and the LTFT remains unchanged. After a few minutes the STFT returns to near zero and the LTFT rises. This test proves that ______.

A) the system is running rich
B) the system is running lean
C) the O₂S sensor is faulty
D) the system is working normally

Question 33

Technician A says a defective injector may cause cylinder misfiring at idle speed. Technician B says restricted injector tips may result in acceleration stumbles. Who is correct?

A) A only
B) B only
C) both A and B
D) neither A nor B

Question 34

Technician A says the TPREL PID is the PCM's closed throttle reference voltage. Technician B says an idle trim relearn procedure should be done whenever a part of the IAC system is replaced or a repair is made to something that affects idle speed. Who is correct?

A) A only
B) B only
C) both A and B
D) neither A nor B

Question 35

Technician A says if a lean condition caused by a vacuum leak, restricted injectors, dirty MAF, clogged fuel filter, or bad fuel pump exists, the LTFT will have a negative number. Technician B says when the O2 sensor has a rich signal, the STFT goes lean to adjust the air/fuel ratio. Who is correct?

A) A only
B) B only
C) both A and B
D) neither A nor B

Question 36

Technician A says throttle body cleaner may be used to clean the IAC motor internal components. Technician B says on some vehicles, IAC motor damage can occur if the pintle is cleaned with throttle body cleaner. Who is correct?

A) A only
B) B only
C) both A and B
D) neither A nor B

Question 37

The voltage signal from most O₂ sensors varies between _____ and _____ volt(s).

A) 0, 1
B) 2, 3
C) 3, 5
D) 9.6, 12

Question 38

The activity of an O2 sensor is best monitored with a ______.

A) lab scope
B) scan tool
C) logic probe
D) noid light

Question 39

Idle learn procedures for ETC [throttle-by-wire]-equipped vehicles are being discussed. Technician A says the learn or relearn procedure should be completed anytime the PCM has been replaced or updated, or after the throttle body has been cleaned or replaced. Technician B says the system does not need to relearn if the battery has been disconnected. The system will automatically go through the procedure when the engine is restarted.Who is correct?

A) A only
B) B only
C) both A and B
D) neither A nor B

Question 40

A rich air/fuel mixture is being discussed. Technician A says oxygen content in the exhaust will be high. Technician B says the O₂ sensor voltage will be high. Who is correct?

A) A only
B) B only
C) both A and B
D) neither A nor B

Question 41

Which of the following should NOT be used to lubricate injector O-rings?

A) silicone grease
B) automatic transmission fluid
C) engine oil
D) all answers are correct

Question 42

An injector balance test requires an injector pulse tester and a ______..

A) tachometer
B) noid light
C) lab scope
D) fuel pressure gauge

Question 43

What could a leak in the fuel pressure regulator or the fuel pump check valve that allows the fuel pressure to slowly bleed down after engine shut down cause?

A) hard starting
B) surging at high speed
C) detonation
D) excessively lean LTFT

Question 44

Injector cleaning is being discussed. Technician A uses a wire brush to clean the tips of the injectors. Technician B soaks the injector in cleaning solvent. Who is correct?

A) A only
B) B only
C) both A and B
D) neither A nor B

Question 45

When cleaning the injectors with a pressurized injector cleaner, prior to starting the engine, ______.

A) remove the fuel pump relay or fuel pump fuse
B) pinch off the fuel return hose
C) connect the can of cleaner to the Schrader valve on the fuel rail
D) all answers are correct

Question 46

Technician A checks GDI [gasoline direct injectors] injectors with a pulse tester. Technician B test GDI injectors with an ohmmeter. Who is correct?

A) A only
B) B only
C) both A and B
D) neither A nor B

Question 47

A/F ratio sensors are being discussed.Technician A says the output voltage of these sensors is much higher than a conventional O₂S [oxygen sensor]. Technician B say when the output of an A/F ratio sensor is looked at with an OBD-II generic scan tool, the voltage range will appear the same as a conventional O2S sensor, 0 to 1 volt. Who is correct?

A) A only
B) B only
C) both A and B
D) neither A nor B

Question 48

With the TP sensor connector disconnected, test the sensor with a(n) ____________________.

Question 49

An APP [accelerator pedal position] sensor is found on vehicles with ______.

A) automatic transmissions
B) automatic traction control
C) throttle by wire
D) GDI [gasoline direct injection]

Question 50

The best tool to verify that the engine is running excessively rich or lean is a(n) ______.

A) fuel pressure gauge
B) manifold vacuum gauge
C) exhaust gas analyzer
D) lab scope

Question 51

Which of the following components can cause excessively high pressure in a returnless fuel delivery system?

A) faulty fuel pressure regulator
B) faulty fuel pressure sensor
C) faulty PCM
D) all answers are correct

Question 52

All late-model engines use at least one ____________________ oxygen sensor.

Question 53

A vehicle with excessively high fuel pressure is being diagnosed. Technician A says the problem could be a restricted fuel return line. Technician B says the problem could be a shorted [closed] fuel pump relay. Who is correct?

A) A only
B) B only
C) both A and B
D) neither A nor B

Question 54

Technician A uses a low-impedance test light to check for an injector pulse. Technician B uses a noid light to check the injector pulse. Who is correct?

A) A only
B) B only
C) both A and B
D) neither A nor B

Question 55

Vacuum leaks in speed density systems can be verified by watching the _____ on a scan tool.

A) O₂S sensor crosscounts
B) IAC counts
C) mass airflow [MAF] voltage
D) delta EGR [exhaust gas recirculation]

Question 56

If the IAC counts are below 16 on a fully warmed up engine, there may be a problem with a(n) ______.

A) faulty ECT [engine coolant temperature]
B) vacuum leak
C) stuck open thermostat
D) misadjusted TP [throttle position sensor]

Question 57

When viewing injector patterns on a lab scope, the injector pulse end with a ______.

A) downward right angle
B) first upward spike
C) highest upward spike
D) last upward spike

Question 58

If liquid gasoline is found in the fuel pressure regulator vacuum hose, ______.

A) replace the vacuum hose
B) replace the pressure regulator
C) replace the fuel pump
D) all answers are correct

Question 59

Technician A says a small leak in the air duct between the MAF and the throttle body will not cause a driveability problem. Technician B says a small intake manifold leak in a speed density system will not cause a driveability problem. Who is correct?

A) A only
B) B only
C) both A and B
D) neither A nor B

Question 60

Cracks and tears in the plumbing between the ____________________ sensor and throttle body are potential air leak sources that can affect the air/fuel ratio.

Question 61

Describe a speed density system.

Question 62

What is the difference between short-term and long-term fuel trim?

Question 63

If a hot-wire type mass airflow [MAF] sensor is contaminated with dirt, the operation of the ____________________ relay should be checked.

Question 64

____________________ are used to locate the source of an internal fuel leak that allows the fuel pressure to drop to zero PSI immediately after engine shut down.

Question 65

On an ETC [throttle-by-wire] system, the APP [accelerator pedal position] and TP [throttle position] sensors are checked using a(n) ____________________.

Question 66

If the injectors and their electrical harness are visible but cannot be accessed without removing the upper intake manifold, injector operation can be checked by using a(n) ____________________.

Question 67

The O₂S [oxygen] sensor should toggle between rich and lean ____________________ to ____________________ times in a ten-second period?

Question 68

A pulse ____________________ injector uses high current to open the injector.

Question 69

When the system is running in open loop mode, the STFT value should be ____________________.

Question 70

A fuel ____________________ is a solenoid-actuated fuel valve.

Question 71

What is the correct procedure for checking an oxygen sensor with a voltmeter?

Question 72

What is the difference between the pulse width of an injector and the duty cycle?

Question 73

Do not use compressed ____________________ to flush or clean the fuel rail.

Question 74

In sequential fuel injection systems, each injector has its own electrical ____________________ circuit and wiring.

Question 75

What is the difference in signal output between an oxygen sensor and an A/F [air/fuel] ratio sensor?

Question 76

What problem may result from dirt buildup on an engine's throttle plates?

Question 77

While testing, a good pressure regulator diaphragm will hold ____________________.

Question 78

A(n) ____________________ is used to test the internal electrical circuit of an injector.

Question 79

Why will a leak in the ductwork between the MAF and the throttle body have an effect on the driveability of the vehicle?

Question 80

____________________ and hold injector circuits use two driver circuits to control injector action.