WRESTLING WITH MODERN DIESELS

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1 WRESTLING WITH MODERN DIESELS BY THOMAS MARCY Winning a bout with a diesel engine means using some heavy-duty skills. And as with any tough match, it pays to know the strengths and weaknesses of your opponent. We don t know much about alligator wrestling (which looks dangerous) or mud wrestling (which looks like tons o fun), but we do know something about diesel wrestling. We say wrestling because working on diesel engines is different from working on gasoline engines you don t get as many in your bays, so you re less familiar with them. This article is meant to change that. Next time you go to the mat with a diesel engine, you may be able to demonstrate a few new holds. As you know, a diesel engine requires no spark plugs to fire the fuel, although glow plugs are typically used to assist engine starts in cold weather. Often, the fuel accumulates slightly before light-off occurs. This is called the delay stage. Once the delay stage concludes, the fuel mixes with the hot compressed air in the cylinders and ignites, causing crunching blows to occur inside the engine. It s because of these crunching blows, plus the fact that the engine produces far greater cylinder pressures than its gasoline-fed cousin, that the diesel has long been the burly power champ that produces high torque. Two Cummins Entries Several contenders have climbed into the ring on the diesel light truck card. One is the Dodge Ram truck s 24- valve Cummins turbo diesel, an inline Six. Featuring big breathing, this engine produces 245 hp with the sixspeed manual transmission, or 235 hp for automatics. Peak torque of 505 ftlb comes in at 1600 to 2300 rpm. Cummins says the 24-valve cylin- 30 January 2002

2 Photo: Paul Weissler der head design increases airflow and improves low-speed performance. The head also features vertical, centered injection nozzles, which are claimed to boost combustion efficiency, cleanliness and fuel economy. Weigh in some electronic fuel control and you ve got a tough opponent. A diesel engine s fuel injection system must possess several characteristics to deliver maximum performance. These include accurate injection control, high-pressure atomization, fast fuel ignition and fuel temperature adjustment capability. Fuel s fiery entry into the cylinders in the Cummins comes via a Bosch VP44 electronic injection pump and electronically controlled timing. First, the engine is cranked up for the match with an electric-powered lift (or supply) pump. Fuel flow begins as the lift pump pulls fuel from the tank and delivers it to the injection pump. As the engine spins over, the rotary, high-pressure injection pump is driven at half the engine speed by a simple front gear train. This simplicity helps cut operating noise. The Cummins-developed ECM receives information from various sensors and controls on the engine, then translates that info into specific fuel quantity and timing commands that are sent to the injection pump metering control. Note that the injection pump used on earlier ( ) Cumminsequipped Dodge turbo diesel pickups is a Bosch P7100 inline design what we sometimes call the jerk pump. The cam-operated six-plunger pump in the jerk pump sends fuel to the injector nozzles. The newer VP44, however, is a rotary job with the ability to vary fuel and injection timing based January

WRESTLING WITH MODERN DIESELS on input from the ECM. This pump incorporates a fuel pump control module (FPCM), which contains fueling, timing and diagnostic data.

3 WRESTLING WITH MODERN DIESELS on input from the ECM. This pump incorporates a fuel pump control module (FPCM), which contains fueling, timing and diagnostic data. The FPCM communicates with the ECM to obtain information on desired fueling and timing. The FPCM responds by consulting the fueling data and timing in its memory, then commands fueling and timing solenoids. The VP44 has a fuel temperature sensor inside it. The pump also contains a speed sensor that gives the FPCM information on the position and speed of the pump shaft. A crankshaft reference pulse that marks TDC of cylinder No. 1 is also sent once every pump revolution. By comparing this reference pulse from the ECM to the position signal from the speed sensor, the FPCM can reference the pump s position to that of the engine. This allows the FPCM to adjust pump timing to compensate for small position differences between the fuel pump shaft and the engine cam. If the difference becomes too great, a fault is logged in the FPCM. The FPCM controls the timing and fueling through two solenoids located in the pump. The timing solenoid controls the position of a cam ring inside the pump by varying internal transfer pump pressure to a cam ring piston. The cam ring has evenly spaced lobes around its inner diameter. The pumping plungers ride on rollers that rotate around inside this ring. The rollers follow the inner diameter of the ring and push the pumping plungers inward whenever a cam lobe is encountered. This builds injection pressure on the fuel trapped between the plungers. By rotating the cam ring with the timing solenoid, the FPCM is able to advance and retard the injection timing by making For Dodge Ram trucks, the 24-valve Cummins diesel provides improved block strength and durability, with reduced noise. Also, the water pump, oil pump, cooler housings and coolant bypass are all integrated to eliminate potential leak points. Photo: Thomas Marcy the rollers contact the cam lobes either earlier or later in their rotation. As its name implies, the fuel solenoid in the pump meters fuel to the injectors. It does this by opening a metering valve to allow fuel from the supply pump to flow into the pumping chamber. Once this chamber is charged with fuel, the solenoid valve closes, trapping the fuel in the chamber and allowing injection pressure to build. The fuel is routed to the correct injection nozzle via the pump distributor head. A port on the distributor rotor aligns with one of the six pump distributor head outlet ports to distribute fuel to a given nozzle. In the cylinder head, the high pressure opens the injector nozzles, allowing fuel to pass into the combustion chamber. Once the desired amount of fuel is injected, the solenoid valve opens, causing the pressure in the pumping chamber to bleed down, which ends injection. The injection nozzle then snaps shut. When the high-pressure fuel reaches the nozzle, the pressure lifts the needle valve against the spring s preset popping tension. At the desired pressure, the nozzle pops open to let the fuel spray into the combustion chamber. A minor fuel leak past the nozzle needle valve enters the fuel drain manifold in the cylinder head. The fuel in the manifold then exits at the rear of the cylinder head and is routed to the fuel tank. Fuel return from the injection pump is also routed back to the tank. Breathing and Belching Both Cummins engines the older Bosch-equipped P7100 and the newer VP44 feature direct injection, sans precombustion chambers. Cummins claims that direct injection produces more power than precombustion chamber-equipped engines, while lowering internal heat stresses. High compression heat and fuel swirl for good combustion develop in the piston s symmetrical combustion bowl. In the late-model Cummins turbo diesel, the valvetrain has wider lobes on the tappet face and cam, with longer push tubes. To reduce camshaft wear, an electric lift pump eliminates the need for a mechanical lift pump lobe. The standard valve springs are compatible with engine braking equipment. Top off the engine with an engine-matched Holset turbocharger and wastegate and you have a unit ready to rumble. For Cummins, a no-smoke entry into the fray is gained with an Integrated Air Intake Grid Heater. Using this method, white smoke is eliminated and cold-starting is improved. After warmup, compression and combustion efficiencies are improved by providing aftercooled air to the engine. 32 January 2002

Also, new electronic devices allow monitoring of critical engine data and diagnostic information from the ECM. For example, with the RoadRelay 4 (RR4) system, you can tap into the ECM while driving.

Also, RR4 can remind the driver when service is due on specific items and can record up to 12 service events.

4 Also, new electronic devices allow monitoring of critical engine data and diagnostic information from the ECM. For example, with the RoadRelay 4 (RR4) system, you can tap into the ECM while driving. Then if a problem develops on the road, the system will display the appropriate fault code. Also, RR4 can remind the driver when service is due on specific items and can record up to 12 service events. Also new for the Cummins 24-valve turbo diesel is QuickCheck II, a diagnostic read-only application that runs on Palm devices and lets you view such items as engine sensor and diagnostic information, including boost pressure, oil pressure, fuel rate, percentage engine load, engine hours, output torque and intake manifold pressure. The QuickCheck II kit contains a custom data link adapter, cables, connectors and the diagnostic software application. Load the software, plug it in and you can view data in real time or download it to your shop PC. Ford s Power Stroke Ford enters the ring with an old hand, but with new tricks. In its Power Stroke Garrett-turbocharged diesel, such as found in an F-250 we recently drove, a mechanical fuel pump nests in the valley behind the fuel filter with its plunger riding on a special engine cam lobe. In older models, the feed pump uses a diaphragm to draw fuel from the tank while a piston-type positive displacement pump increases the 4 to 6 pounds of pressure to around 50 psi, regulated by a spring and plunger in the filter housing. The 50 psi is delivered to the lower chamber inside the injector through a common rail passage in the cylinder head. The tiny fuel chamber plunger s oil-pressure-driven head is seven times the size of the bottom of the plunger, where the fuel is delivered. The head forms the chamber floor that receives a burst of high oil pressure. This happens as an electrical solenoid valve opens and lets the pressure in. The high oil pressure pulse drives the plunger down, multiplying the pressure by a factor of seven at the injector tip. The trapped fuel blows out Photo: Thomas Marcy GM growls in V8 style with the new Duramax The engine features many aluminum components and an electronic common rail fuel system. the injector tip and into the cylinder. The PCM operates the injector solenoids through an injector driver module. The fuel comes to the solenoids from an injection control pressure sensor, a sensor in the oil rail at the front of the driver s side head. An injection pressure regulator (IPR) rides in the high-pressure oil pump. This pump mounts similar to the older-design injection pump. The fuel enters both the left and right cylinder head high-pressure feed hoses. During a cold start, the highpressure oil pump receives unfiltered oil from the low-pressure lubrication pump through the left-side valve lifter oil galley and through the antidrainback Diesel engines need and consume large quantities of air. Always check the air filter and examine the manometer gauge to look for restrictions. January

WRESTLING WITH MODERN DIESELS When servicing a diesel engine, always check the maker s specs to see what type of oil and fuel filters the engine uses.

Once the engine starts, or during warm engine starts, the check valve closes and the high-pressure oil pump receives filtered oil from the pump reservoir.

5 WRESTLING WITH MODERN DIESELS When servicing a diesel engine, always check the maker s specs to see what type of oil and fuel filters the engine uses. Because of the stresses of compression-ignition, diesels require oil with a unique lubrication character and additive package. check valve. Once the engine starts, or during warm engine starts, the check valve closes and the high-pressure oil pump receives filtered oil from the pump reservoir. The high-pressure pump then supplies the oil under extremely high pressures through the left and right pressure rails. A relief valve in the high-pressure oil pump regulates the available pressure. The control pressure actually delivered to the oil rails is regulated electronically by an injector control pressure (ICP) regulator, controlled by the PCM. Once in the oil rail, the oil is fed to the head s fuel injector bores through four galleys drilled and machined in the cylinder head. The highpressure oil then activates the fuel injectors based on PCM commands. The GMC & Chevy Tag Team GMC and Chevrolet enter the ring with a new 6.6-liter turbocharged diesel V8 called the Duramax Although no lightweight in power, the Duramax weighs only 836 pounds. It uses aluminum extensively in such key components as the cylinder heads, crankcase, accessory drive brackets, intake manifold and flywheel bellhousing. The engine is available in 2500 HD and 3500 GMC Sierras, and in Chevrolet Silverado pickups and chassis cabs. The Duramax cylinder head is made of gravity-cast aluminum and has four valves per cylinder. Each fuel nozzle is Photos: Thomas Marcy located in the center of the combustion chamber in a stainless-steel holder. The valve arrangement forms a twisting intake airflow. The intake ports are designed to maximize tangential flow for optimum intake swirl. In this head, adequately and evenly cooling the valve seats helps minimize any change in the valve gap. The Duramax fuel system has a supply pump, a function block, common rails and injectors. An eccentric shaft drives the three-plunger supply pump, which is driven at crankshaft speed. The pump s inlet has a gear-type feed pump and a rail pressure control valve, which is governed by a sensor attached to the function block, on the high-pressure side. The valve is controlled in response to driving conditions. Each injector has a PCM-controlled solenoid in the injector s upper portion. According to GM, one advantage of a common rail system is that injection pressure can be raised regardless of engine speed. This means the size of the nozzle hole in the injector can be small, which when used in conjunction with high-pressure injection, makes for a finer spray and faster combustion. This, by the way, makes a good case for offering timely filter services. Don t let your customer get pinned to the mat. Battery condition is a very important part of any diesel s performance, especially during cold-weather months when glow plugs help supply initial combustion chamber heat. 34 January 2002

Using short-duration, high-pressure injection improves performance in the final exhaust emissions rounds.

6 The Duramax 6600 is a relatively high-speed engine as far as diesels go, with a rated speed of 3100 rpm. Faster combustion makes possible shorter injection times, which means optimum fuel economy and exhaust emissions even at those higher speeds. Using short-duration, high-pressure injection improves performance in the final exhaust emissions rounds. However, because there are higher levels of NO X (oxides of nitrogen) with highpressure injection at the start of the process, injection timing must be retarded. But GM says that if the timing is retarded without pilot injection, NO X reduction is limited while particulate matter increases. GM claims that pilot injection overcomes these limitations. Injecting a very small pilot amount of fuel before TDC makes it easier for the main injection to ignite. This makes it possible to retard injection timing and reduce both NO X and particulate levels. Another benefit GM claims for pilot ignition is reduced noise. Generally, combustion noise becomes louder as injection pressure increases. According to GM, pilot injection makes it possible to prevent a rapid increase in injection pressure during main injection, which greatly reduces diesel knock. Always check for proper turbocharger and wastegate function. Although tucked far beneath the cowl on this Ford pickup truck, a simple vacuum pump test can reveal a wastegate servo knocked out of the match. The engine management system and control module of the Duramax are basically the same as with gasoline engines, with vehicle-related control items also being similar. However, the common rail system required developing new software for diesel injection control items. Other new software was developed for self-diagnostic items, such as injection volume, injection timing, pilot injection control, rail pressure control and injector dwell. The ECM drives the injectors by way of an electronic driver unit (EDU), which also senses and ignores abnormal injection requests. The engine management system also performs all OBD II functions. In servicing these new diesel engines, you can easily see that a technician first needs to know the basic operation of these oil-burners. But he must also know the quirks applicable to each powerplant. Also, training in the DTCs that an ECM/PCM can throw into the ring becomes very important. You d be well-advised to get a ringside seat and do some serious manual studying on the art of diesel wrestling. Who knows? You could be called on for the next match! With a stumbling Cummins-equipped Dodge, some technicians crack open an injection nozzle line to check for cylinder power output. Instead, we suggest using a contact pyrometer on the exhaust manifold to isolate the offending cylinder. Visit to download a free copy of this article. Copies are also available by sending $3 for each copy to: Fulfillment Dept., MOTOR Magazine, 5600 Crooks Rd., Troy, MI January

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