he d be amazed at how his original invention has evolved. Since the diesel engine was first patented in 1894, its performance

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Sabrina Goodwin
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1 28 May 2010

COMMON RAIL DIESEL COMESINTOITS OWN BY BOB PATTENGALE Common rail diesels add sophisticated electronic components and controls to the simplicity of the original diesel engine design.

2 COMMON RAIL DIESEL COMESINTOITS OWN BY BOB PATTENGALE Common rail diesels add sophisticated electronic components and controls to the simplicity of the original diesel engine design. Servicing these modern engines requires an understanding of how they work, plus the proper tools. Illustration courtesy Robert Bosch LLC If Rudolf Diesel were alive today he d be amazed at how his original invention has evolved. Since the diesel engine was first patented in 1894, its performance and efficiency have improved, but the primary fuel delivery process has remained relatively unchanged. The fuel injectors require high-pressure fuel for optimum performance, and this is delivered using a mechanical pump driven by the engine. For the first 100 years, electronic interaction was limited to glow plugs, lowpressure fuel supply and the helpful water-in-fuel warning sensors. For many diesel technicians, this was considered a blessing, because early diesel systems did not require the use of multimeters, scan tools or lab scopes. The introduction of full electronically controlled common rail diesel (CRD) systems has changed the game. The historical analogy is the evolution of transmission design, where early transmission diagnostics required application knowledge and a pressure gauge. I m sure you can think of a few transmission technicians who struggled with added electronic interaction. The key is gaining the knowledge necessary to properly diagnose these systems. Why CRD technology? Performance and fuel economy are the primary driv - ers. Consumers are looking for diesel vehicles that provide higher horsepower, greater torque, better fuel economy and lower noise and vibration. All these improvements must meet stringent EPA and CARB emissions standards. May

Rail Pressure Sensor Gear Pump Suction Throttle (M-PROP) Common Rail Pressure Limiter Valve High- Pressure Pump Fuel Filter With: Water Separator Heater (optional) Tank Fig.

Various vehicle manufacturers might use minor variations, but the basic diesel engine design is the same. Mechanically controlled diesel systems are not precise enough to offer these improvements.

3 Rail Pressure Sensor Gear Pump Suction Throttle (M-PROP) Common Rail Pressure Limiter Valve High- Pressure Pump Fuel Filter With: Water Separator Heater (optional) Tank Fig. 1 This illustration shows the components of the Bosch Second Generation Common Rail System for passenger cars. Various vehicle manufacturers might use minor variations, but the basic diesel engine design is the same. Mechanically controlled diesel systems are not precise enough to offer these improvements. How quickly do you need to learn about CRD systems? In 2007, diesel engine vehicles represented approximately 5% of the overall vehicle fleet. Pilot Injection Prefilter CRD Multiple Injection Main Injection Other Actuators ECU Post Injection Other Sensors Fig. 2 There are three stages of CRD injection: pilot injection, which is meant to reduce combustion noise and pollutant emissions; main injection, which provides the energy needed for engine performance; and post injection, which is designed to reduce particulates and regenerate the diesel particulate filter. Accelerator Pedal Engine Speed (crank) Engine Speed (cam) Illustration: Harold A. Perry Injector (1... n) High Pressure Low Pressure The number of such vehicles has steadily increased, and many predict that by 2020, diesels will represent 20% of the vehicle fleet. To put this in perspective, many predict hybrids will represent only 10% of the vehicle fleet by The first CRD passenger cars were introduced in 1999 and most vehicle makers are working on versions for North America. Technicians working on Ford Powerstroke, Dodge Cummins or GMC Duramax vehicles have already been dealing with this technology. Before we begin describing the CRD systems, one critical note of caution: The high-pressure fuel system can exceed 28,000 psi, so all service and repair should be performed according to manufacturers recommendations. This article will provide you with a basic overview of CRD systems and offer a few repair tips. Vehicle manufacturer-specific components will vary, but the overall concept is the same. Fig. 1 above shows the Bosch Second Generation Common Rail System for passenger cars. Let s take a look at how this system works. The first step in the operation of a CRD system is the fuel supply to the high-pressure pump. In this system, a mechanical gear pump is attached to the rear of the high-pressure pump and is driven by that pump. The gear pump creates a suction that draws fuel from Illustration courtesy Robert Bosch LLC 30 May 2010

1 2 3 4 5 6 7 8 9 10 the fuel tank through the filter. The suction is approximately 2 to 10 in./hg. The gear pump outlet fuel pressure is approximately 65 to 90 psi.

not work. Both injector designs utilize a pressure differential process to overcome the extreme pressure. Solenoid Valve Injectors Illustration A below shows the injector in a rest position.

In the rest position, pressure is equalized between chambers 6 and 9, but you ll notice that there s an inlet restrictor (14) between 6 and 13.

4 the fuel tank through the filter. The suction is approximately 2 to 10 in./hg. The gear pump outlet fuel pressure is approximately 65 to 90 psi. Some vehicle manufacturers use an he fuel injectors described here Twork under extreme pressure, so a simple opening and closing of the injector needle as with conventional gasoline injectors will not work. Both injector designs utilize a pressure differential process to overcome the extreme pressure. Solenoid Valve Injectors Illustration A below shows the injector in a rest position. High-pressure fuel is applied to the inlet (13) and distributed to chambers 6 and 9. In the rest position, pressure is equalized between chambers 6 and 9, but you ll notice that there s an inlet restrictor (14) between 6 and 13. The solenoid valve ball (5) is seated via the solenoid armature (4) and solenoid valve spring (11), which prevents fuel from entering into the return line (1). The nozzle needle (16) is seated using the nozzle spring (7) and pressure equalization between 6 and 13. Illustration B shows the injector opening. The solenoid coil (2) is triggered by the pickup current from the ECM. The electromagnetic force overcomes the solenoid valve spring (11), which allows the solenoid armature (4) and valve ball (5) to open. As soon as the valve ball unseats, fuel from the valve control chamber (6) is returned via the fuel return passage (1). This begins the chain reaction: The inlet restrictor (14) allows the electric fuel pump, which is normally mounted inside the fuel tank. The fuel pump provides fuel to the high-pressure pump through the fuel filter. Average fuel pump pressure is 55 to 65 psi. Solenoid Valve & Piezoelectric Injectors A B C pressure in the valve control chamber (6) to be lower than the pressure in the chamber (9). The higher pressure pushes against the pressure shoulder of nozzle needle (8) and overcomes the nozzle spring. Fuel is then sprayed into the cylinder via the injection orifice (10). Illustration C shows the injector closing. The solenoid coil (2) is released and the solenoid valve spring (11) seats the solenoid armature (4) and valve ball (5). The overstroke spring (3) protects the valve ball from damage by slowing down the solenoid armature. Piezoelectric Injectors How do piezoelectric injectors work? The piezoelectric actuator consists of a piezoelectric stack, push pin and electrode wires. The 30mm (1.2-in.) stack contains more than 350 layers of piezoelectric material. When voltage is applied to the stack, the dimensions of the piezoelectric crystals change momentarily because the atoms are mutually displaced. This effect produces a.040mm ( in.) increase in length. Piezoelectric injectors use charge and discharge stages to open and close the injector. The lab scope screen capture above demonstrates the charge and discharge stages. The blue line represents voltage, the red line amperage. The charge and discharge stages are demonstrated The second step is fuel volume control to the high-pressure pump. The magnetic proportional valve (M-PROP) is used to control the volume of fuel supplied to the high-pressure pump. by the red line. The charge stage begins with the positive amperage section and the discharge stage begins with the negative amperage section. With the fuel injector in a rest position (below), the low-side fuel system (1) fills the control chamber, which is located just above and below (4) during startup. High-pressure fuel (2) fills the servo valve (5) and nozzle module (6) chambers; this keeps the nozzle needle seated using the same pressure equalization described for solenoid valve injectors. When the fuel injector opens, the piezoelectric actuator module (3) is charged by the ECM. It pushes down on the hydraulic coupler (4), which then depresses the servo valve. There s a fuel chamber between 4 and 5, which compensates for differences in the length of individual parts due to thermal expansion. Once the servo valve opens, fuel is allowed to return via 1, which creates a similar pressure differential between 5 and 6, as described above. The high-pressure passage (2) pushes up on the nozzle needle and allows fuel to spray into the combustion chamber. When the fuel injector closes, the ECM activates the piezoelectric discharge stage, which causes the piezoelectric stack to retract, closing the servo valve. As you can see, both injectors work a little differently, but both accomplish the same task delivering high-pressure 1 2 fuel to the cylinders. Understanding the differences will help you diagnose the system correctly. Opening and closing the injectors one time per 3 firing event at high pressure can be accomplished mechanically, so why 4 do we need all the electronics? With 5 an electronically controlled multiple-injection 6 process, injectors can be opened as many as five times 7 per firing event. Illustrations courtesy Robert Bosch LLC 32 May 2010

For example, if the RPS indicates the fuel rail pressure is low, the pulse width is decreased, allowing more fuel to enter the high-pressure pump, in a sense operating in a closed-loop strategy.

5 The M-PROP is controlled by the engine control module (ECM) using a variable pulse width. The ECM increases and decreases the high-pressure pump volume based on vehicle operating conditions and information supplied by the rail pressure sensor (RPS). For example, if the RPS indicates the fuel rail pressure is low, the pulse width is decreased, allowing more fuel to enter the high-pressure pump, in a sense operating in a closed-loop strategy. Vehicle manufacturers will use different names, but the goal is the same control fuel volume. Some other names for this sensor are fuel quantity solenoid, fuel control actuator and fuel volume control valve. At the top of the high-pressure pump in Fig. 1 on page 30 you ll see a yellow return line. Not shown in this diagram is a cascade overflow valve (COV), which regulates how much fuel is used for pump lubrication and how much is returned to the fuel tank. The COV is spring-loaded and reacts to pressure Fig. 3 Diagnosing common rail diesel systems requires a high level of scan tool interaction. This GM Tech 2 recording of a 2005 GMC pickup verifies which cylinders are functioning normally and which are lagging behind. buildup on the low-pressure side of the system. The COV works together with the M-PROP to maintain a proper balance in the low-pressure system. Next, a high-pressure pump builds supply pressure for the fuel injectors in the common rail. Fig. 1 shows the highside pressure in red. Once again, keep 34 May 2010

in mind that fuel pressure can exceed 28,000 psi on some applications. The RPS is used by the ECM to keep the fuel rail pressure consistent with operating conditions.

This is similar to a fuel pressure regulator on a conventional fuel system.

6 in mind that fuel pressure can exceed 28,000 psi on some applications. The RPS is used by the ECM to keep the fuel rail pressure consistent with operating conditions. The pressure limiter valve is a dualstage mechanical valve. The first stage relieves overlimit excessive pressure and the second stage helps maintain pressure at a predetermined level. This is similar to a fuel pressure regulator on a conventional fuel system. Finally, the ECM opens and closes the fuel injectors at the appropriate time using the crankshaft (CKP) and camshaft (CMP) position sensors. The ECM re- Injector Map Without IQA Fig. 4A Injector Map With IQA Fig. 4B CRD fuel injectors are very sensitive and require precise calibration. Every injector receives a unique injector code for ECM injector quantity adjustment (IQA). These charts show the difference between preforming and not performing an IQA. 36 May 2010

quires both the CKP and CMP for the vehicle to start. The vehicle will continue running without the CMP, but the engine will die if the CKP signal is lost.

7 quires both the CKP and CMP for the vehicle to start. The vehicle will continue running without the CMP, but the engine will die if the CKP signal is lost. Two types of fuel injectors are used for most applications solenoid valve injectors and piezoelectric injectors. The sidebar on page 32 ( Solenoid Circle #24 Circle #23 Circle #25 Circle #23 Valve & Piezoelectric Injectors ) explains how these injectors function. The CRD injection process is divided into three basic stages: pilot injection, main injection and post injection (Fig. 2, page 30). Let s take a look at each stage. Pilot injection is designed to reduce combustion noise and pollutant emissions. Up to two pilot injections are possible. During pilot injection, the pressure in the cylinder is slightly raised, which causes a shorter delay in the main event combustion. The benefit is reducing peak combustion pressure, which in turn reduces combustion noise. Pilot injection is also used to reduce particulate matter. Main injection provides the energy for the performance of the engine, allowing it to produce peak torque and performance. Post injection is designed to reduce particulates and regenerate the diesel particulate filter (DPF). Post injection 2 occurs toward the end of combustion and is designed to reduce the level of soot particles produced. Post injection 1 takes place 40 ATDC or later. This brings hydrocarbons to the oxidation catalyst for catalyst regeneration. The decision to provide post injection 1 is based on information from the differential pressure sensor. Diagnosing CRD systems is very similar to diagnosing fuel-injected gasoline engines. Using a scan tool and lab scope will be critical to efficient and accurate diagnosis and repairs. Fig. 3 on page 34 is a scan tool recording from a 2005 GMC pickup. The engine was running rough with reduced power, and no diagnostic trouble codes were present. The scan tool recording pointed the technician in the right direction by quickly identifying which cylinders were not contributing. From the scan tool data we can also confirm that the Desired and Actual Fuel Rail Pressures are within specification, so our issue is not related to fuel pressure. This condition will be specific to cylinders 4 and 6. Figs. 4A and 4B on page 36 show two charts. The first chart, Injector Map Without IQA (Injector Quantity Adjustment), shows what happens when the adjustment is not performed. The blue lines represent fuel injectors that are lagging behind the red injectors. This would reduce fuel delivery to the cylinders and limit power and torque. The second chart, Injector Map With IQA, shows the injectors after the IQA, which matched the injectors to the ECM. If you re going to repair 38 May 2010

Fig. 5 Figs. 4A and 4B on page 36 show the need to perform an injector quantity adjustment following injector replacement.

5 is a capture from a 2007 Dodge Ram 2500 6.7L diesel engine showing the current fuel injector codes stored in the ECM.

If this vehicle has been to other shops and a driveability problem still exists, you might want to make sure the injector codes were entered properly.

8 Fig. 5 Figs. 4A and 4B on page 36 show the need to perform an injector quantity adjustment following injector replacement. This screen capture shows the actual procedure being performed with a scan tool on a 2007 Dodge Ram CRD vehicles, this will be a scan tool must-have feature. Fig. 5 is a capture from a 2007 Dodge Ram L diesel engine showing the current fuel injector codes stored in the ECM. Keep in mind the numbers stored are only as good as the person who input the data. If this vehicle has been to other shops and a driveability problem still exists, you might want to make sure the injector codes were entered properly. Changing the code is simple: Type in the new code and click Start to store the code. No matter how sophisticated diesel electronic systems get, you must always remember the basics. This engine lacked performance, but the only fix it needed was a new filter and a pack rat nest cleaning. CRD systems are equipped with additional sensors and actuators not discussed in this article. Most of these components are common to fuel injection systems accelerator pedal position sensor, inlet air pressure sensor, boost pressure sensors, etc. The sensor information might be supplied directly to the ECM or received from another module. It s important to understand your specific vehicle application to avoid chasing something that might be caused by another module. Scan tool reprogramming capability is a must-have when working on CRD vehicles. Every driveability issue should begin with a verification of module calibration. In some cases, the only repair is updating the ECM with new software. One final note: Don t forget to check the basics. The photo at left is from a vehicle that lacked power and exhibited driveability issues. The only repairs required were a new air filter and a filter inlet cleaning and a call to the pest control people. Common rail diesel systems are just getting started, so now is the time to learn what makes them tick. If you do, you ll be prepared to diagnose and fix them when they start showing up in your bays. This article can be found online at Circle #23 40 May 2010

Automotive Fuel and Emissions Control Systems 4/E

Automotive Fuel and Emissions Control Systems 4/E Opening Your Class KEY ELEMENT Introduce Content Motivate Learners State the learning objectives for the chapter or course you are about to cover and explain