In 1994, Ford introduced the new breed of Navistar engine to its truck line called the Power Stroke. The Power Stroke was still a 7.3 engine that was redesigned and now known as a DIT (Direct Injected Turbo).
The engine came standard with a turbo made by Garrett. At first, the engine was turbocharged without an intercooler. If you look on the turbo outlet of the compressor side of the turbo you can see that a “Y” pipe is connected to direct air from the turbo into the intake manifold. The reason for no intercooler was the size of the turbo.
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In 1999, Ford introduced an intercooler for the same 7.3 DIT engine. The intercooler was put into production on the Ford trucks because there was a change in the turbo. The compressor wheel was larger and the change to a bigger turbo brought more boost and higher exhaust gas temperatures. The new turbo was capable of maximum boost of 28 psi, which needed to be controlled.
Garrett installed a wastegate, mounted in the turbine side of the turbo. There is a wastegate actuator mounted on the compressor side of the turbo, connected to the wastegate by a rod. So when the compressor housing makes boost beyond what is needed, the actuator opens the wastegate.
In 2003, Ford introduced the 6.0 DIT engine for its Diesel trucks with a turbo known as variable geometric turbo (VGT) made by Garrett for this engine.
As engine speed rises, the powertrain control module (PCM) commands a solenoid to open at a desired rate to change the geometry of the “vanes” in the turbine housing. This is used to operate from no boost at idle to full boost at wide open throttle (WOT).
Before the Power Stroke, Diesels were generally defined as indirect injection (IDI) engines. When the Power Stroke was introduced by the International Corporation new terminology came into use: direct injection (DI). Direct injection is used on the 7.3- and 6.0-liter engines. The use of computer control and direct injection made for less emissions and more power, bringing Ford’s Diesel engines into the modern age.
With DI, Diesel fuel is pressurized electronically at the injector of the cylinder that is being fired. Other manufacturers were using electronic systems for Diesel injection, but they were also using an external pump to pressurize the Diesel fuel. The International Corporation used engine oil under high pressure along with various sensors and lines to make Diesel fuel pressure at the injectors.
7.3 Fuel Supply
Fuel is stored in the tank and must be pressure-fed to the fuel injectors. On the 7.3 from 1994 to 1997, fuel came from the tank through fuel lines to a mechanical engine-driven pump, which is located in the central valley of the engine behind the turbocharger.
One side of the pump is the inlet, used to suction fuel from the tank and deliver it to the fuel filter basket. The fuel pressure coming into the fuel filter basket is anywhere from 3 to 7 psi. On the other side, at the fuel filter basket is a water separator drain.
When entering the second stage, fuel is compressed further and sent to the cylinder-head mounted fuel injectors at 40 psi.
6.0 Fuel Supply
The 6.0 fuel system is very similar to that on the later 7.3. This system has an electric pump known as a horizontal fuel conditioning module (HFCM). The HFCM is framemounted, and is controlled by the engine’s computer. The condensation drain (water separator) is integrated into the pump, as is a serviceable prefilter.
The Power Stroke oiling system is not radically different than that of other internal combustion engines. The only major design differences are the high-pressure path required by the high pressure oil pump (HPOP) and the oil cooler.
There are differences in the HPOP systems of the 7.3 and 6.0. Even though their functions are similar, the differences are worth noting. There are two system types: the lowpressure system and the high-pressure system.
7.3 Low-Pressure System
The oil pump in the 7.3 engine is of a “gerotor” design. As the crankshaft spins, the gear on the front turns the rotor (vane) inside the oil pump. Oil is drawn through the pickup screen mounted in the oil pan.
When oil reaches the pump it is then pressurized and sent through the front cover. The front cover has two passages by which the oil enters the block. One passage leads to the separator drain. When entering the second stage, fuel is compressed further and sent to the cylinder-head–mounted fuel injectors at 40 psi.
7.3 High-Pressure System
In order for the oil to enter the HPOP reservoir, it must pass through a check-ball assembly integrated into the front of the block. During cold starts, the HPOP receives unfiltered oil through the check-ball passage until reaching a nominal operating temperature.
When oil enters the HPOP, it is pressurized and sent through hoses that run to both cylinder heads.
Oil then travels through the high-pressure passages to surround each injector. When the injector is fired, the oil drives the internal piston down inside the injector body. After the piston in the injector is driven down and the piston returns to the top the oil is “spit” out of the injector through an orifice mounted on the side of the top of the injector.
The oil then drains back through holes leading to the oil pan.
6.0 High-Pressure System
The 6.0 HPOP is housed in the rear of the motor. The crankshaft, camshaft, and HPOP are gear driven from the rear of the engine. The front of the engine has no gears other than the crankshaft, which turns the engine oil supply gerotor pump. As the HPOP spins from the rear geartrain, it pressurizes oil received from the reservoir. The pressurized oil exits the HPOP into a pump discharge line.
The design of HPOP system in the 6.0 DI is more efficient than that in the 7.3 DI. If any leaks occur in the system they are contained by the crankcase.
If a leak occurres on a 7.3, it can be detrimental. If the high-pressure hoses come apart oil can spray everywhere, cause engine damage, and make a huge mess. The design of the 6.0 system came about by problems faced with the 7.3. The HPOP system on the 6.0 is more of a task to service, but most of the time it’s trouble-free.
The cooling system of the Power Stroke engine does employ one component you may not be familiar with: the degas bottle. This small tank is mounted separately from the radiator and serves as the service point for the cooling system. The service cap is mounted on the degas bottle, as it is mounted higher than the radiator (which has no cap).
In general, the cooling system of the 7.3 engine is reliable. Even in the event of adding aftermarket products (such as programmers and upgraded turbos), the coolant system has proven itself to be efficient. Typical wear parts (such as water pumps and thermostats) are to be expected, but it’s rare to experience a head gasket repair or oil cooler failure.
6.0 Engine Cooling System
The 6.0 engine utilizes many of the same components as the 7.3 engine. One thing that you need to address is the exhaust gas recirculation (EGR) cooler. In 2004, EGR valves became mandatory. The EGR systems did pose a problem when this engine was introduced. From 2004 to 2006, Navistar had some serious complaints with the EGR systems on the 6.0 engines. Additionally, head gaskets became a problem and plagued the 6.0 engine. Blown head gaskets were overheating engines and destroying them.
One head gasket problem was the material, but there are only four bolts per cylinder to secure them (compared to the six bolts per cylinder of the 7.3). Hard use over extended periods placed serious pressure on the head gaskets.
There are two solutions for the problematic EGR cooler. One is to totally eliminate the EGR from the engine. Keep in mind that this is for off-road use only. If you remove this for highway use, it is not emissions compliant.
The second solution is to replace the EGR cooler. Bulletproof Diesel sells a stainless-steel EGR cooler with a more rigid design, which offers more strength and cooling efficiency. Using this product is a great option instead of having to replace the factory cooler and carries a lifetime warranty.
In the 7.3 cylinder head, you have one intake valve and one exhaust valve. They both are the same size, 1.68 inch diameter. From 1994 until 2002, the 7.3 cylinder head remained the same. The injectors and glow plugs are under the valve cover.
When the 6.0 was released in 2003, many changes had taken place, including the cylinder heads. This was the first head from Navistar with four valves per cylinder (two intake valves and two exhaust valves). Valves measure at 1.33 and the exhaust valves measure 1.10 inches in diameter.
The cylinder head took on a totally new configuration to help meet the emissions standards. To increase port swirl, the valves were positioned in a twisted configuration in relation to the cylinder. The Diesel engine is dependent upon port swirl and with this valve layout, the combustion process is more refined and efficient.
Glow plugs from the 6.0 now have removable sleeves. On the 7.3 engine, the glow plugs thread into the top of the cylinder head in a “cast” boss leading to the combustion chamber. As for the 6.0 engine, the glow plugs are sealed by a stainless-steel sleeve. The sleeve seals off the injector and the combustion chamber from coolant.
Because the 6.0 cylinder head has four valves per cylinder, two intake valves have to be opened at the same time along with two exhaust valves. The rocker arms are different from the 7.3 in relation to design and length. Also, the rocker arms incorporate a bridge linking the two.
Something else to note is the injector hold-downs. On the 7.3 engine the injector has a hold-down that is on the injector body. There are two bolts positioned from top to bottom where the injector sits in the cylinder head. The top bolt is installed into the cylinder head and tightened to its specific torque specification. Then the injector is installed into the cylinder head and the hold-down is positioned over the bolt already installed. Once it is in position the other bolt can be installed.
As for the 6.0, the injector holddown is much easier to deal with. The hold-down is shaped like a horseshoe and is removable from the injector body. One caution: take care when installing the injector in the 7.3 or 6.0. Make sure to grease the O-rings on the injector along with the injectors cup in the cylinder head. Then install the injector and press it into the head by hand or with a soft rubber hammer. Do not strike the injector with a blunt object because this can damage the injector.
The “up pipe” carries the exhaust gas from the manifold to the turbo. This pipe connects to the turbo through a “Y” pipe. The Y is cast iron and directs exhaust flow to the turbine chamber in the turbo.
For the 7.3 engine, before the exhaust enters the “down pipe” it must pass through an exhaust backpressure valve (EBV), which is a flap in the end of the turbine housing on the exhaust exit side of the turbo. In simple terms, the EBV flap can open or close to restrict the exhaust flow.
The EBV is used by the PCM of the engine to help aid in warm-up in cooler temperatures. This provides more heat to the coolant for interior heat when the outside temperature is below 45 degrees F and the oil temperature is below 167 degrees F.
6.0 Engine Exhaust
In order to meet the demands of tighter emissions in 2003 Navistar introduced the 6.0 engine, the government demanded that manufacturers reduce the amount of nitrogen oxide in Diesel engines.
The 6.0 engine incorporates an exhaust gas recirculation (EGR) valve.
Selective Catalyst Reduction (SCR) is something new and has just been released for Ford trucks. The SCR system uses urea (odorless, colorless, non-toxic substance found in urine of mammals) as the catalyst.
The urea used in the exhaust system is in liquid form. This liquid can be purchased at most local parts stores as Diesel exhaust fluid (DEF). DEF is made from a concentration of liquid urea plus a percentage of deionized water.
A truck has two tanks inside the fuel filler door. One is for the Diesel exhaust fluid (DEF) (blue lid) and the other is for Diesel fuel (green lid). When using urea, there is no need to use an EGR valve.
But the draw back is that now the engine makes nitrous oxide. So to eliminate that, urea is injected through a nozzle downstream in the exhaust system somewhere shortly after it exits the turbo. The urea reacts with the nitrous oxide, turning it into ammonia. The ammonia enters the catalytic converter, where it is separated into nitrogen and water.
The new SCR system is the best choice for reduction in emissions for Diesel engines. Yes, there is an expense of the DEF, but in return you make more power and obtain better fuel economy.
In 1994, when the Power Stroke engine was introduced, it was the first computer-controlled Diesel for the mid-size truck. The engine design was known as a HEUI (hydraulically actuated, electronic controlled unit injector). There were some other Diesel engines on the road that had some functions that were computer controlled, but not the entire engine.
Glossary of Terms
Accelerator Pedal Position (APS) Sensor
The APS is attached to the accelerator pedal and is a part of the pedal assembly. The engine has no throttle cable attached to the accelerator pedal. As the pedal is depressed to the floor, the sensor sends a voltage reading to the PCM. The PCM reads the voltage and determines that if the accelerator pedal has been depressed then more fuel needs to be given to the engine. This type of system is also known as “fly-by-wire.”
Barometric (BARO) Pressure Sensor
This sensor is located behind the instrument panel. The engine’s computer references this sensor to indicate changes in altitude, which affect the quantity of fuel and changes in the timing.
Camshaft Position (CMP) Sensor
The CMP is also called a “hall effect” switch. It uses magnets to signal position. The camshaft has a “tone” wheel. This wheel is made up of slots and teeth. As the teeth of the tone wheel pass the magnets of the sensor, voltage is produced. When the slots pass by the sensor, magnetism drops off and crankshaft position can be established and referred to by the computer.
The PCM uses the frequency from the crankshaft position (CKP) sensor and CMP to determine engine speed and position. The PCM also conditions the signal from the CMP to be used as the tachometer reference in the instrument cluster.
Crankshaft Position (CKP) Sensor
This sensor receives pulses from a tone wheel mounted on the crankshaft of the engine. It works very similarly to the function of the CMP. The CKP determines crankshaft speed, position, and acceleration. This information is used as input to the computer for misfire detection and the control of fuel to the cylinders through the injector driver module (IDM).
The CKP was not used for the 7.3 engines. On the crankshaft of the engine is a slotted target wheel, 58 evenly spaced teeth, and a slot on the wheel that is the width of two teeth that have been removed (known as the SYNC gap). As the crankshaft spins, the teeth pass the magnetic field of the sensor which causes a voltage frequency. The voltage frequency continues until it passes the minus-2 slot that causes a drop in frequency. The frequency changes and the minus-2 slot is used by the PCM to determine engine speed and position relative to top dead center (TDC).
Engine Coolant Temperature (ECT) Sensor
The ECT sensor is used on both the 7.3 and 6.0 engines. The sensor tells the computer the temperature of the engine coolant. The computer then uses this information to control functions of the engine. The ECT sensor is located in the thermostat housing.
Engine Oil Pressure (EOP) Sensor
This sensor is used for dash instrumentation only. The EOP is not read by the PCM. The EOP switch closes when oil pressure reaches 5 to 7 psi. The normal engine oil pressure in the 6.0 engine ranges from 5 to 70 psi. Engine Oil Temperature (EOT) The EOT works much like a coolant temperature sensor. PCM reads the resistance in order to determine oil temperature.
Exhaust Back Pressure (EBP)
The EBP is used to measure the exhaust pressure inside the exhaust manifold. The readings taken by the PCM from the EBP sensor will be to control the EBP valve and to help aid in warm up. Second, the EBP voltage signal indicates to the PCM the performance of the turbo.
Valve Exhaust Gas Recirculation (EGR)
When certain parameters of the PCM are reached such as engine speed, coolant temp, oil temp, etc., the EGR is commanded to open. The purpose of this actuator is to open and allow exhaust gas to enter the intake manifold. How far it opens is also determined by the PCM from parameters of the engine at that time.
This actuator was introduced on the 6.0 engine in order to reduce emissions.
Fuel Injector Control Module (FICM)
In order for the injectors to pulse from the signal sent to the computer from the CMP sensor, the computer must use a device to pulse the injector, the FICM on a 6.0 (or the injector driver module, IDM, on a 7.3). In simple terms, this is a transformer box. For the injectors to pulse under great loads takes more than 12 volts. The voltage needed to pulse such an injector is around 120 volts.
Power Stroke engines use a glow plug system. Like spark plugs in gasoline engines, these plugs ignite incoming fuel to start the engine. Unlike spark plugs, glow plugs maintain heat and ignite the fuel when compression levels reach a combustible point. The hotter the glow plugs are, the lower this compression point needs to be.
A “Wait to Start” light in the dash alerts the driver to hold off turning the key until the glow plugs have reached their predetermined heat range.
With growing technological advances, 6.0 engines use a glow plug control module (GPCM). This module works like the glow plug relay on 7.3 engines. The biggest difference is that it can control the glow plugs individually.
The GPCM module is controlled by the ECM, and if a glow plug failure occurs, it alerts the computer of its functionality for diagnostics.
On both engine systems, the computer may even cycle the glow plugs when the engine is running. It all depends on the temperature readings given to the computer. After the engine has warmed to normal operating temperature and has been turned off, the glow plugs may not be used at all to restart. It depends on the feedback the ECM receives from the sensors.
Injection Control Pressure (ICP) Sensor
The ICP tells the computer what pressure is being produced by the HPOP. Then the computer controls the regulator on the demand for the desired oil pressure. It is much like the one used for the 7.3 engines. The ICP is a variable capacitance sensor that is the “eyes” for the PCM to determine pressure being produced by the HPOP.
On the 7.3 engine, there is an injector driver module (IDM). Instead of using an IDM on the 6.0 engine, International used the fuel injector control Module (FICM).
Injection Pressure Regulator (IPR)
The IPR is mounted on the HPOP and controls the amount of oil pressure being generated in the HPOP. It controls how much oil being delivered by the engine oil pump enters the HPOP to be pressurized. Basically, the IPR is an adjustable regulator that is controlled by the PCM to help maintain proper needed pressure of the HPOP.
The injector of the Power Stroke is where the “HEUI” name is derived. The injector is actuated by high-pressure oil from the HPOP. The injector has a solenoid mounted on top and when energized by the injector drive module (IDM) uses the high pressure oil to squeeze Diesel fuel through the injector’s tip. The solenoid takes 100 volts and 7 amps to energize.
The 6.0 injectors are much like the ones used for the 7.3 engine. They both have to use high-pressure oil from the HPOP in order for the plunger of the injector to be driven down. In the 7.3 engine, highpressure oil is delivered to the injector by a “barrel” cast into the cylinder head. The high-pressure oil surrounds each of the injectors in the cylinder head. When the injectors coil is energized, high-pressure oil is allowed in to drive the plunger down.
The 6.0 injector is a lot smaller than the 7.3 with fewer O-rings.
Intake Air Temperature (IAT) Sensor
It works very similar to the engine oil temperature (EOT). Inside is a thermistor that produces resistance to the PCM to help determine temperature. As the intake air temperature increases, the resistance decreases. The IAT is mounted in the intake air cleaner to provide the PCM with information on the outside air temperature. The PCM uses this information to determine the need for the use of the exhaust back pressure (EBP) control to aid in warming the engine.
Mass Air Flow (MAF) Sensor
This sensor is used to determine the amount of air that enters the engine. The MAF is mounted between the air filter and turbo inlet. Inside the MAF is an element that is heated. As outside air is pulled in by the engine, it passes across the heated element inside the MAF. As the air passes across the heated element, it cools the element. This generates a signal back to the PCM to determine fueling requirements in proportion to how much air is being taken in by the engine.
Manifold Absolute Pressure (MAP) Sensor
This sensor is also used in gasoline engines to measure atmospheric pressure inside the intake manifold. The difference in this application is the use of a turbocharger. As the accelerator pedal is pushed down and the pressure rises inside the intake manifold, the computer makes changes in the fuel distribution to the cylinders.
Power Control Module (PCM)
The PCM contains three microprocessors: the engine, chassis, and transmission. The three microprocessors work together from information provided by various sensors from the engine, transmission, and chassis to determine a fueling strategy for the engine. The PCM sends a 5-volt reference to the sensors, except for the crank and cam sensors, which generate their own voltage for the PCM. The PCM uses nine sensors from the engine microprocessor and four from the chassis microprocessor to finetune the engine.
Written by Bob McDonald and Republished with Permission of CarTech Inc
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