Question 1

Technician A says that most transfer pumps used on diesel CR systems are of the external gear type. Technician B says that most transfer pumps used on diesel CR systems use a non-positive pumping principle. Who is correct?

Accepted Answer

Technician A is correct because most transfer pumps used in diesel Common Rail (CR) systems are indeed of the external gear type, which is a positive displacement pump, contrary to Technician B's statement about a non-positive pumping principle.

Question 2

How many pump cylinders are used in a Caterpillar CR system high pressure pump?

Accepted Answer

The answer of How many pump cylinders are used in...

Question 3

Technician A says that most Bosch CR high pressure pumps are lubricated with diesel fuel. Technician B says that Caterpillar CR high pressure pumps are lubricated with engine oil. Who is correct?

Accepted Answer

Most Bosch Common Rail (CR) high-pressure fuel pumps are indeed lubricated by the diesel fuel they pump, while Caterpillar's high-pressure fuel systems, particularly in older models, use engine oil for lubrication. This reflects the design differences between manufacturers and their approach to lubricating these critical components.

Question 4

If actual rail pressure falls below desired rail pressure in a diesel CR system, which of the following should occur?

Accepted Answer

When actual rail pressure falls below the desired rail pressure in a diesel Common Rail (CR) system, the rail pressure control valve directs more flow to the rail to increase the pressure. This is because the system needs to maintain a specific pressure for optimal injection and combustion.

Question 5

If the rail pressure limiter valve trips open in a typical CR fuel system, which of the following should be true?

Accepted Answer

The rail pressure limiter valve in a Common Rail (CR) fuel system is designed to open when the rail pressure exceeds the highest specified system pressure, to protect the system from excessive pressure that could cause damage.

Question 6

What is the function of the quill tube used in many diesel CR systems?

Accepted Answer

The quill tube in many diesel Common Rail (CR) systems connects the rail high pressure pipes to the Electro-Hydraulic Injectors (EHIs) through the cylinder head, ensuring the precise delivery of fuel to the injectors.

Question 7

When a CR high pressure line is removed for any reason, which of the following steps is required practice by many engine OEMs?

Accepted Answer

The answer of When a CR high pressure line is...

Question 8

Which of the following is another way of saying base timing when referring to multipulse capable, CR fuel systems?

Accepted Answer

Base timing in the context of multipulse capable, Common Rail (CR) fuel systems refers to the start of the first injection pulse. This is when the initial amount of fuel begins to be injected into the combustion chamber, setting the timing foundation for subsequent pulses.

Question 9

When a typical CR-EHI is energized by the injector driver, which of the following occurs first?

Accepted Answer

When a typical Common Rail Electro-Hydraulic Injector (CR-EHI) is energized by the injector driver, the pressure in the valve control chamber collapses first. This is because the energizing of the injector opens a valve that allows the high-pressure fuel to escape from the control chamber, reducing its pressure and enabling the main injection process to start.

Question 10

Technician A says that CR EHIs with piezo actuators respond faster to energization by the injector drivers than those with solenoid actuators. Technician B says that current CR EHIs using piezo actuators tend to be slimmer and more compact than those with solenoid actuators. Who is correct?

Accepted Answer

The answer of Technician A says that CR EHIs with...

Question 11

What term is used by Caterpillar on their CR EHIs to code their injection quantity calibration data for programming to the ECM?

Accepted Answer

E-Trim is the term used by Caterpillar on their CR EHIs (Common Rail Electro-Hydraulic Injectors) to code their injection quantity calibration data for programming to the ECM (Engine Control Module). This allows for precise control of fuel injection for optimal engine performance.

Question 12

Technician A says that an EHI with a piezo actuator is capable of breaking up a single injection cycle into up to 7 separate pulses. Technician B says that during a CR EHI multipulse injection cycle, the pressure rises through each successive pulse. Who is correct?

Accepted Answer

Technician A is correct because piezo actuators in electronic hydraulic injectors (EHI) can indeed break up a single injection cycle into multiple pulses, up to 7. Technician B is incorrect because the pressure does not necessarily rise with each successive pulse in a common rail (CR) multipulse injection cycle; the pressure is controlled and maintained by the system.

Question 13

What explains why EHIs with Piezo actuators respond faster to energization signals from the injector drivers?

Accepted Answer

Piezo actuators respond faster because their mechanical movement is directly initiated by the application of an electrical voltage, which causes an immediate change in shape or size without the need to build a magnetic field, unlike solenoid actuators.

Question 14

Technician A says that adaptive trim (A-Trim) evaluates and corrects EHI fuel flow at set intervals to ensure balanced cylinder fueling. Technician B says the A-Trim feature makes initial fuel flow programming (E-Trim/ QR-codes/ Cal-codes) unnecessary. Who is correct?

Accepted Answer

Technician A is correct because adaptive trim (A-Trim) is designed to adjust and correct fuel flow to ensure each cylinder receives a balanced amount of fuel over time. Technician B is incorrect because the A-Trim feature does not eliminate the need for initial fuel flow programming (E-Trim/QR-codes/Cal-codes); it complements it by making ongoing adjustments after the initial programming.

Question 15

What is used to time a Caterpillar CR fuel system high pressure pump to the engine?

Accepted Answer

The timing pin is used to time a Caterpillar CR fuel system high pressure pump to the engine. This method involves aligning the pump at a specific point in its rotation with the engine's crankshaft to ensure proper timing for fuel injection.

Question 16

What is the function of the admission valve used in some diesel CR fuel systems?

Accepted Answer

The admission valve in diesel common rail (CR) fuel systems holds the high-pressure fuel away from the nozzle seat until it is energized, allowing precise control of fuel injection timing and quantity.

Question 17

What force is used to hold the nozzle valve seated and closed on a typical CR-EHI when the engine is running?

Accepted Answer

The nozzle valve in a typical Common Rail Electronic Hydraulic Injector (CR-EHI) is held seated and closed by a combination of spring and hydraulic force when the engine is running. This ensures precise control over fuel injection.

Question 18

Which of the following best explains why some OEMs state that the high pressure pipes used on CR systems should not be re-used?

Accepted Answer

The seats in high-pressure pipes used in Common Rail (CR) systems deform to create a seal when they are initially torqued. This deformation is designed to ensure a perfect seal under high pressure. If these pipes are removed and then reused, the seal may not be as effective because the deformation has already occurred, potentially leading to leaks or other failures. This is why OEMs recommend against reusing these pipes.

Question 19

Which of the following is the ECM output used to manage rail pressure at any given moment of operation in a diesel CR fuel system?

Accepted Answer

The rail pressure control valve is the ECM output used to manage rail pressure in a diesel Common Rail (CR) fuel system. It adjusts the pressure by controlling the amount of fuel delivered to the high-pressure pump, ensuring optimal engine performance and efficiency.

Question 20

Technician A says that an advantage of CR-EHIs is that they are less susceptible to problems caused by contaminated fuel than other types of fuel injector. Technician B says that when a CR-EHI fails due to contaminated fuel, the problem can be usually rectified by disassembly, cleaning, and reassembly. Who is correct?

Accepted Answer

The answer of Technician A says that an advantage of...

Quiz 30: Common Rail Systems