Engine Performance A8
Technician A says if the firing voltage is higher than normal the burn time will decrease. Technician B says if the firing voltage is lower than normal the burn time will decrease. Who is correct?
A
A breakout box is used to: Monitor signals received by the computer. Monitor changes in adaptive strategies. Display diagnostic trouble codes. All of the above.
Monitor signals received by the computer.
A digital signal may be called a squarewave signal.
T
SFI is a type of PFI fuel system.
T
The third digit of a DTC indicates whether the code is an SAE or manufacturer-specific code.
T
The supercharger is driven by:
crankshaft
A low voltage signal from the O2 sensor indicates: A rich air/fuel mixture A lean air/fuel ratio A stoicheometric air/fuel ratio None of the above
A lean air/fuel ratio
A flashing MIL indicates: A fuel system malfunction that may damage the O2 sensor. A misfire that may damage the catalytic converter. Both A and B Neither A nor B
A misfire that may damage the catalytic converter.
Piezoresistive sensors measure: temperature changes. pressure and mechanical strain. manifold vacuum. manifold pressure.
pressure and mechanical strain.
In an EGR system with a pressure transducer, the pressure transducer is used to: Stop EGR flow when the engine coolant temperature is to low. Control EGR flow according to engine rpm. Control EGR flow according to throttle position. Shut off EGR flow in case of a backfire.
Control EGR flow according to engine rpm.
The triggering device in the ignition system is sometimes referred to as a: Camshaft position sensor. Crankshaft position sensor. Throttle position sensor. Vehicle speed sensor
Crankshaft position sensor.
Which type of fuel injector has a relatively high current applied to quickly open the pintle, then the current is reduced to lower level. Peak and hold injectors Pulse width modulated injectors Duty cycled injectors High side driver injectors
Peak and hold injectors
Excessive CO emissions may be caused by: Lean air-fuel mixtures. Rich air-fuel mixtures. Lower than normal fuel pressures. Ignition system misfires.
Rich air-fuel mixtures.
The camshaft position sensor in a GM fast start system is used to: Sequence the injectors properly. Sequence the ignition coils properly. Both A and B Neither A nor B
Sequence the injectors properly.
Which of the following is not part of the primary circuit? Ignition coil Ignition switch Ignition module Spark plugs
Spark plugs
Modules that are not part of any vehicle network are called: Output driver modules Input driver modules Stand alone modules Both A and B
Stand alone modules
A bent fan blade should be straightened.
T
A defective radiator cap may cause the upper radiator hose to collapse when the coolant is cold.
T
A good indication of engine load is the amount of vacuum formed during the intake stroke.
T
A muffler is a component installed in the exhaust system to reduce or eliminate the engine's postcombustion noise.
T
A scan tool is a device that interfaces and communicates with the vehicle's computer.
T
An infrared analyzer may be used to test the efficiency of the catalytic converter.
T
Analog multimeters should be used for testing delicate electronic devices.
T
At increased RPM and less time between coil firings, electronic dwell begins earlier to allow for coil saturation.
T
Cylinders having excessive blowby may cause oil to be present in the air cleaner.
T
Detonation may be caused by excessive ignition spark advance.
T
Enable criteria are the conditions that have to be met in order for the PCM to run a specific test of a system.
T
Fuel pressure should be relieved prior to disconnecting fuel system components.
T
Fuel system pressure should be relieved with the engine running.
T
If a sensor signal is within its normal range but is sending false information the vehicles computer will display a trouble code.
T
Ignition cables are usually made of solid wire which acts as a resistor in the secondary circuit.
T
In addition to measuring HC and CO levels, a four gas analyzer also monitors carbon dioxide (CO2) and oxides of nitrogen (NOx).
T
In an OBD II system the PCM will set a code if the evaporative system has a leak as small as .020" in size.
T
In an OBD II vehicle the technician may be able to erase trouble codes without erasing freeze frame data.
T
Inertia switches turn off the fuel in case of a severe impact.
T
It takes two complete camshaft revolutions and one revolution of the crankshaft to complete one engine cycle, firing all cylinders once.
T
Long-term fuel trim learns permanent changes performed by short-term fuel trim.
T
Many modules have to be reprogrammed for the vehicle if they are to be replaced.
T
Spark plug thread taps may be used to help repair damaged O2 sensor threads.
T
Spark plugs with iridium tips should not be re-gapped.
T
Surging at low speeds or a rough idle may occur if the EGR valve is stuck closed.
T
The OBD II AIR system is meant only to operate long enough to warm the exhaust and help promote catalytic converter light-off by burning left-over HC and CO in the exhaust manifold of a cold engine.
T
The digital EGR is comprised of three solenoids that all flow different amounts of EGR.
T
The idle air control motor works by varying the position of the throttle plate.
T
The ignition coil is both a primary and secondary ignition component.
T
A hot-range spark plug has a shorter heat path than a cold-range spark plug.
TRUE
The best way to check the efficiency of individual cylinders is: Four gas analysis A Snap throttle test A Vacuum test A power balance test
A power balance test
Black smoke from the exhaust is caused by: Oil entering the combustion chamber A rich air/fuel ratio A lean air/fuel ratio Coolant entering the combustion chamber
A rich air/fuel ratio
Injector pulse width is: The diameter of the injector spray pattern. How far the PCM opens the injector. The amount of time the injector is held open and injecting fuel. The percentage of time the injector is held open and injecting fuel.
The amount of time the injector is held open and injecting fuel.
The Resource Conservation and Recovery Act basically states that hazardous material users are responsible for hazardous materials from the time they become waste until. The material leaves the shop. A certified inspector determines the material is non-toxic. 20 years after the materials leave the shop. The proper waste disposal is completed.
The proper waste disposal is completed.
Bi-directional control means: The computer is able to move an output in two different directions The technician can tell a computer to exercise an output The technician can reprogram the computer None of the above
The technician can tell a computer to exercise an output
The PCM has the option of turning the MIL off when the diagnostic test which caused the MIL to light passes for:
Three consecutive trips
The best place to find the most amount of data about a specific vehicle is
VIN
Hybrid vehicles may be classified as: Mild Strong Parallel Both A and C
Both A and C
An O2 sensor may be used to: Monitor the air/fuel ratio. Monitor the temperature of the exhaust gas. Monitor the condition of the catalytic converter. Both A and C.
Both A and C.
Basic timing is the initial timing specified by the:
manufacturer
An oscilloscope is a type of voltmeter that displays voltage over time graphically with a trace.
true
Enable criteria must be met in order for the PCM to run a system monitor.
true
When checking a solenoid with an ohmmeter, there should be an infinity reading on the meter if the solenoid is good.
true
The acceptable amount of alcohol mixed with gasoline is:
up to 10 percent.
Vacuum is formed on a pistons Intake stroke Compression stroke Power stroke Exhaust stroke
Intake stroke
With gasoline direct injection the fuel is injected: Into the intake manifold Above the throttle plates Into the combustion chamber None of the above
Into the combustion chamber
Technician A says Fuel injectors may be cleaned by soaking them in solvent. Technician B says it is also a good idea to use a wire brush to unclog injectors. Who is correct?
NEITHER
The intake manifold tuning valve makes the intake manifold:
BOTH
An IAC valve stuck in the closed position may cause all of the following except:
High idle speed.
Technician A says in a COP system the PCM can adjust ignition timing for each individual cylinder. Technician B says firing order in a COP system is controlled by the IC modules.
A
Technician A says in a central port injection system fuel pressure ranges from 54 to 64 psi. Technician B says fuel pressure in a port fuel injection system is typically higher than fuel pressure in a central port injection system. Who is correct?
A
Technician A says one component of the secondary ignition circuit is the spark plug. Technician B says the module is a component in the secondary ignition circuit. Who is correct?
A
Technician A says the fuel rail delivers fuel to the fuel injectors. Technician B says The throttle body in a port fuel injection system controls the amount of fuel entering the engine Who is correct?
A
Technician says If a timing belt or chain becomes excessively worn, it is possible that a change in valve timing accuracy will result. Technician B says The crankshaft is driven by the camshaft. Who is correct?
A
A technician may help prevent injuries and damage to vehicles by Regularly observing all shop rules Operating all vehicles in a safe manner Maintaining a clean work area All of the above
ALL
A cooling system pressure tester may be used to Test the effectiveness of the antifreeze in the coolant Test the cooling system for leaks Test the radiator cap Both B and C
BOTH
High fuel pressure may be caused by: A defective fuel pressure regulator A fuel return line that is restricted A faulty PCM Both A and B
BOTH
In addition to ignition control, a Hall effect switch can also be used to:
BOTH
Technician A says A reducing catalyst takes NOx and converts it into N2 and O2. Technician B says The O2 released from the NOx in the reducing catalyst is used to help oxidize the CO and HC. Who is correct?
BOTH
Technician A says each module in a CAN system receives every communication on the serial data bus. Technician B says Only the messages with the correct heading are responded to by a module in a CAN system.
BOTH
Technician A says long term fuel trim works to bring short term fuel trim close to zero percent correction. Technician B says If a lean condition exists because of a vacuum leak, the long term fuel trim will have a plus (+) number on the scan tool. Who is correct?
BOTH
Technician A says the basic advantage of the snapshot feature on a scan tool is the ability to look at the existing conditions when a code was set. Technician B says GM failure reports do the same thing as a snapshot but also include any fault stored in memory, not just those related to the emissions-related circuits. Who is correct?
BOTH
Technician A says to relieve pressure on an EFI system, a pressure gauge may be connected to the fuel pressure test port and the bleed valve on the gauge opened with the bleed hose installed in an approved container. Technician B says before fuel system components on an EFI system can be removed, the fuel system pressure must be relieved. Who is correct?
BOTH
The vent valve in an evaporative emissions system may be: Opened to allow fresh air through the charcoal canister. Closed with the purge valve open while the PCM monitors the fuel tank pressure sensor for vacuum Closed to prevent the system from purging. Both A and B
BOTH
What does a high CO level in the exhaust gas indicate?
High CO level in the exhaust gas indicates a rich air/fuel mixture.
When using a four gas analyzer on an engine with a lean air/fuel ratio: CO reading will be higher than normal and O2 readings will be lower than normal. HC readings will be lower than normal and CO2 readings will be higher than normal All readings will be higher than normal CO readings will be lower than normal and O2 readings will be higher than normal
CO readings will be lower than normal and O2 readings will be higher than normal
Throttle body fuel injection systems provide improved fuel metering when compared to: Sequential port fuel injection systems Central port fuel injection systems Carburetors All of the above
Carburetors
