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Exam 17: Exhaust Gas Recirculation

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Question 21

Multiple Choice

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Technician A says that oxygen sensors used by diesel engines adjust air-fuel ratios. Technician B says that oxygen sensors can be used to adjust the amount of EGR gas metered into the cylinders. Who is correct?

A) Technician A
B) Technician B
C) Both A and B
D) Neither A nor B

E) A) and B)
F) A) and C)

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Question 22

Multiple Choice

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Two technicians are describing high- and low-pressure exhaust gas recirculation systems. Technician A says that non-cooled, high-pressure EGR flow dominates at low speed, low load conditions and transitions to more flow from the cooled, low-pressure EGR circuit. Technician B says that with an air intake throttle located downstream or after the EGR valve, the throttle plate can open and close to change the pressure differential. Who is right?

A) A only"
B) B only"
C) Both A and B
D) Neither A nor B"

E) B) and D)
F) All of the above

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Question 23

Multiple Choice

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What is measured by comparing exhaust temperature entering and leaving the cooler?

Which EGR system draws EGR gas into the cylinders through the turbocharger compressor inlet?

Technician A says that EGR systems lower in-cylinder NOx formation by reducing peak cylinder pressures and temperatures. Technician B says EGR systems reduce NOx emissions by reducing displaced air in the cylinder. Who is correct?

The presence of a noxious reddish-brown tint to the atmosphere over cities when the winds are light indicates an abundance of:

Which of the following measures pressure in the exhaust manifold?

Technician A says that diesel engines that use EGR systems often have longer engine break-in periods. Technician B says that the use of EGR gas introduces abrasive soot into the cylinders, which shortens the break-in period. Who is correct?

The cooler bundle is attached to the housing only through contact with:

What test allows the service technician to override the EGR valve position by commanding different EGR valve positions and monitoring the actual position feedback from the valve?

Which of the following is NOT a requirement of EGR valve design features?

Technician A says that diesel engines use MAF sensors to measure exhaust airflow into the cylinders. Technician B says that exhaust gas does not pass through an MAF sensor, so the MAF sensors cannot measure exhaust gas flow. Who is correct?

Two technicians are discussing exhaust gas recirculation diagnostics. Technician A says that when diagnostic codes are set, the ECM will disable the EGR operation. Technician B says that significant differences between a sensed EGR control vacuum and a commanded vacuum signal will trigger diagnostic trouble codes. Who is right?

Which of the following environmental problems is caused primarily by NOx emissions?

What device is used by internal EGR systems to force EGR gas into cylinders?

Which of the following mechanisms does NOT form a closed-loop feedback circuit for the EGR valve?

Technician A says that turbocharger boost pressures are higher in EGR engines to compensate for power loss when using EGR gas. Technician B says that higher boost pressures are used to ensure that the combustion chamber receives an adequate amount of oxygen to support combustion. Who is correct?

Two technicians are discussing EGR monitor. Technician A says that under the correct operating conditions, the OBD manager may briefly open the EGR valve and measure the drop in turbocharger speed against expected values. Technician B says that during monitoring, the turbocharger speed will drop because combustion temperature is cooler at low EGR flow rates. Who is right?

Two technicians are discussing exhaust gas recirculation diagnostics. Technician A says that if any data are out of range or irrational when compared to other data, then the malfunction indicator lamp (MIL) will illuminate. Technician B says that several variables are monitored by the OBDII system of diesel EGR with the key off. Who is right?

What device is used by internal EGR systems to force EGR gas into cylinders?