Chapter 33 & 34:
Technician A says that an EGR valve that is stuck open can cause idle problems. Technician B says that a stuck closed EGR can increase HC emissions. Who is correct?
Both A and B
At what temperature do nitrogen atoms combine with oxygen atoms to form NOx?
2,300-2500 degrees
Technician A says the purge solenoid is normally closed. Technician B says the vent solenoid is normally open. Who is correct?
Both A and B
Which of the following statements about EVAP systems is not true? a. If the system is purging vapors from the charcoal canister when the engine is running at high speeds, rough engine operation will occur. b. Cracked hoses or a canister saturated with gasoline may allow gasoline vapors to escape to the atmosphere, resulting in gasoline odor in and around the vehicle. c. Rough idle, flooding, and other similar conditions can indicate a saturated canister. d. A vacuum leak in the system can cause starting and performance problems.
A
Explain why a small PCV valve opening is adequate at idle speed.
It is enough to move blow-by from crankcase
Technician A says that during oxidation, as NOx gases pass over the catalyst, the N atoms are pulled from the NOx molecules and are absorbed by the catalyst. The released oxygen atoms then flow through the converter to the second bed. The result of NOx oxidation is pure nitrogen plus oxygen or carbon dioxide. Technician B says that during the reduction phase inside the converter, hydrocarbon and carbon monoxide molecules experience a second combustion. The result of this combustion or oxidation process is water vapor and carbon dioxide. Who is correct?
Neither A nor B
While discussing PCV valve operation: Technician A says that the PCV valve opening is decreased at part-throttle operation compared to idle operation. Technician B says that the PCV valve opening is decreased at wide-open throttle compared to part throttle. Who is correct?
Neither A or B
Name the three types of emissions being controlled in gasoline engines.
Fuel Evaporation, Blow-by gases (Pre), & Exhaust gases (Post)
Rather than relying on the AIR system for extra oxygen in a TWC, what do most late model vehicles do to support the oxidation process?
PCM
Why is a PCV system critical to an engine's durability?
Prevents sludge. Sludge causes worn pistons, piston rings, valves, bearings, and other internal engine parts.
What types of catalyst are typically used to reduce NOx and to oxidize HC and CO?
TWC
An EGR valve that does not fully close can cause all of the following except ___
detonation
A restricted catalytic converter can cause all of the following except ___
increased power at high speeds
In a negative back-pressure EGR valve, if the exhaust pressure passage in the stem is plugged, the bleed valve remains ________________.
closed
The most likely cause of a EVAP related code is:
A damaged or loose fuel fill cap
What is a catalyst?
Any substance that speeds a chemical reaction without itself being changed.
As a catalytic converter begins to deteriorate, the signal from the post-catalyst HO2S becomes ___ the signal of the pre-catalyst HO2S. a. shorter than b. more like c. larger than d. flatter than
B
Which of the following exhaust gases is typically not measured during an I/M 240 test? a. HC b. O2 c. NOx d. CO
B
The PCV system prevents ________________ _______________ from escaping to the atmosphere.
Blow-by gases
Technician A says that the AIR system should pump air into the exhaust manifold(s) during engine warmup. Technician B says that the secondary air system check valve can be checked with an exhaust gas analyzer. Who is correct?
Both A and B
While diagnosing the cause of high HC and O2 emissions: Technician A says that the HC may be elevated because of an ignition problem. Technician B says that the O2 may be elevated because of an ignition problem. Who is correct?
Both A and B
While discussing EGR valve diagnosis: Technician A says that a defective throttle position sensor may affect the EGR valve operation. Technician B says that a defective engine coolant temperature (ECT) sensor may affect the EGR valve operation. Who is correct?
Both A and B
While discussing PCV system diagnosis: Technician A says that a defective PCV valve may cause rough idle operation. Technician B says that satisfactory PCV system operation depends on a properly sealed engine. Who is correct?
Both A and B
While discussing automotive emissions: Technician A says that oxygen emissions are monitored because they are an indication of the completeness of the combustion process. Technician B says that the conditions for minimizing HC emissions are the same as those that cause high NOx emissions. Who is correct?
Both A and B
While discussing electric exhaust gas recirculation (EEGR) systems: Technician A says that some are air cooled. Technician B says that some are cooled by engine coolant. Who is correct?
Both A and B
While discussing evaporative (EVAP) systems: Technician A says that the coolant temperature has to be above a preset value before the PCM will operate the canister purge solenoid. Technician B says that the vehicle speed has to be above a preset value before the PCM will operate the canister purge solenoid. Who is correct?,,
Both A and B
While discussing the proper way to test a catalytic converter: Technician A says that a pressure gauge can be inserted into the oxygen sensor bore and the back pressure caused by the converter measured. Technician B says that restrictions in the converter can be checked with a vacuum gauge while the engine is being quickly accelerated. Who is correct?
Both A and B
All of the following are considered harmful emissions EXCEPT: a. Hydrocarbons b. Carbon Monoxide c. Oxygen d. Oxides of Nitrogen
C. Oxygen
The primary post combustion control is the
Catalytic converter
What should you do if a leak is not detected during a leak test?
Check for loose or corroded components
How much pressure does a typical EVAP pressure tester apply to the system during testing? a. 14 in. Hg b. 14 psi c. 1 in. H2O d. 0.5 psi
D
Which of the following statements about carbon dioxide is not true? a. CO2 levels are highest when the air-fuel ratio is slightly leaner than stoichiometric. b. The production of CO2 is directly related to the amount of fuel consumed; therefore, more fuel-efficient engines produce less CO2. c. To reduce CO2 levels in the exhaust, engineers are working hard to decrease fuel consumption to keep CO2 low. d. The concern for CO2 emissions is one of the primary reasons for the delayed use of alternative fuels for automobiles.
D
Which of the following systems is designed to reduce NOx and has little or no effect on overall engine performance?
EGR
A vehicle is setting a lean exhaust code and the HO2S data shows the exhaust to be very lean. Technician A says a malfunctioning AIR system may be the cause. Technician B says a clogged EGR may be the cause. Who is correct?
Technician A
While discussing PCV systems without a PCV valve: Technician A says that blow by gases are routed into the intake manifold through a fixed orifice tube. The system works the same as if it had a valve, except that the system is regulated only by the vacuum at the orifice and the size of the orifice. Technician B says that VVT systems eliminate the need for a PCV system. Who is correct?
Technician A
While discussing catalytic converter diagnosis: Technician A says that Mode $06 data should be checked. Technician B says that a good converter is evident by low amounts of CO2 in the exhaust. Who is correct?
Technician A
While discussing tailpipe emissions and cylinder misfiring: Technician A says that cylinder misfiring causes a significant increase in HC emissions. Technician B says that cylinder misfiring results in a large in-crease in CO emissions. Who is correct?
Technician A
When discussing the diagnosis of a positive back pressure EGR valve: Technician A says that with the engine running at idle speed, if a hand pump is used to supply vacuum to the EGR valve, the valve should open at 12 in. Hg of vacuum. Technician B says that with the engine not running, any vacuum supplied to the EGR valve should be bled off and the valve's diaphragm should not move. Who is correct?
Technician B
While diagnosing a PCV problem: Technician A says that a stuck open PCV valve will cause a richer than normal air-fuel mixture. Technician B says that oil in the air cleaner assembly can be caused by a restricted PCV hose. Who is correct?
Technician B
While discussing EGR systems with a differential pressure feedback electronic (DPFE) sensor: Technician A says that the DPFE sensor sends a signal to the PCM in relation to intake manifold pressure. Technician B says that the PCM corrects the EGR flow if the actual flow does not match the requested flow. Who is correct?
Technician B
While discussing EGR valve diagnosis: Technician A says that if the EGR valve does not open, the engine may hesitate on acceleration. Technician B says that if the EGR valve does not open, the engine may detonate on acceleration. Who is correct?
Technician B
While discussing EVAP testing: Technician A says that most OEMs recommend that clean, high-pressure shop air be used to pressurize the system to test for leaks. Technician B says that nitrogen is typically used to drive the smoke through the system when checking the system with a smoke machine. Who is correct?
Technician B
While discussing SCR systems: Technician A says that they are used in place of a conventional catalytic converter to reduce NOx, CO, and HC. Technician B says that the most common reductant used is SCR systems is an ammonia-like substance called urea. Who is correct?
Technician B
Technician A says evaporative emission systems are considered post combustion control. Technician B says positive crankcase ventilation is considered pre-combustion control. Who is correct?
Technician B only
When diagnosing an EVAP system code, Technician A starts by verifying that the system is leaking. Technician B says a scan tool is used to conduct this test. Who is correct?
Technician B only
What is the purpose of the EGR system?
To lower combustion chamber temperature
