ENGINE 3508B
777D OFF-HIGHWAY TRUCK
ENGINE
Shown is the 3508B twin turbocharged and aftercooled engine used in the 777D Update Off-highway Truck.
The engine performance specifications for the 777D Update truck are:
- Serial No. Prefix: 2GR
- performance spec: 0K1144--1000 hp 0K1145--920 hp
- max altitude: 2288 m (7500 ft.)
- gross power: 746 kW (1000 hp) or 686 kW (920 hp)
- full load rpm: 1750
- high idle rpm: 1937
- stall speed rpm: 1540 to 1670
These engines utilize the Electronic Unit Injection (EUI) system for power, reliability and economy with reduced sound levels and low emissions.
NOTE: On the 777D Update truck, the horsepower can be changed from 686 kW (920 hp) to 746 kW (1000 hp) by programming the Engine ECM with the ET service tool.
Engine Electronic Control System
Shown is the electronic control system component diagram for the 3508B engines used in the 777D Update trucks. Fuel injection is controlled by the Engine Electronic Control Module (ECM).
Many electronic signals are sent to the Engine ECM by sensors, switches and senders. The Engine ECM analyzes these signals and determines when and for how long to energize the injector solenoids.
When the injector solenoids are energized determines the timing of the engine. How long the solenoids are energized determines the engine speed.
Occasionally Caterpillar will make changes to the internal software (personality module) that controls the performance of the engine. These changes can be performed by using the WinFlash program that is part of the laptop software program, Electronic Technician (ET). ET is used to diagnose and program the electronic controls used in Off-highway Trucks. If using the WinFlash program, a "flash" file must be obtained from Caterpillar and uploaded into the existing ECM personality module.
The 777D Update truck engines are designed to meet the US Environmental Protection Agency (EPA) Tier I emissions regulations for engines over 560 gross kW (750 gross hp). To meet this regulation the 777D Update truck engine will use a new Emission Software. When installing the new Emission Software "flash" files in an Engine ECM, ET can use the American Trucking Association (ATA) Data Link or the CAT Data Link. The ATA and CAT Data Links consist of a pair of twisted wires that connect to the Engine ECM and the diagnostic connector in the cab. The wires are twisted to reduce electrical interference from unwanted sources such as radio transmissions
The Engine ECM will provide a "Pull-up Voltage" to the signal circuit of most sensors when the ECM senses an OPEN circuit. Frequency sensors do not receive a Pull-up Voltage. The signal circuit is usually Pin C of the 3-pin sensor connectors. The Pull-up Voltage for most sensors is approximately 6.50 Volts, but this value can vary with different electronic controls. Generally, the Pull-up Voltage will be higher than the high value of a sensor's normal range. For example, the normal range of a coolant temperature sensor is 0.4 to 4.6 Volts with temperatures between -40°C and +120°C (-40°F and +248°F). The Pull-up Voltage of 6.50 Volts for this sensor is greater than the normal 4.6 Volts high value.
To test for Pull-up Voltage, use a digital multimeter set to "DC Voltage," and use the following procedure (key start switch must be ON):
1. Measure between Pin B (analog or digital return) and Pin C (signal) on the ECM side of a sensor connector before it is disconnected. The voltage that is associated with the current temperature or pressure should be shown.
Disconnect the sensor connector while still measuring the voltage between Pins B and C. If the circuit between the ECM and the sensor connector is good, the multimeter will display the Pull-up Voltage
Engine ECM
Fuel injection and some other systems are controlled by the Engine ECM (1) located at the front of the engine. Other systems controlled by
the Engine ECM are: ether injection, engine start function and engine oil pre-lubrication.
The Engine ECM has two 40-pin connectors. The connectors are identified as "J1" (2) and "J2" (3) Be sure to identify which connector is the J1 or J2 connector before performing diagnostic tests.
The Engine ECM is cooled by fuel. Fuel flows from the fuel transfer pump through the ECM to the secondary fuel filters.
A 2-pin timing calibration connector (4) is located next to the ECM. If the engine requires timing calibration, a timing calibration sensor (magnetic pickup) is installed in the flywheel housing and connected to the timing calibration connector
Using the Caterpillar ET service tool, timing calibration is performed automatically for the speed/timing sensors. The desired engine speed is set to 800 rpm. This step is performed to avoid instability and ensures that no backlash is present in the timing gears during the calibration process. Timing calibration improves fuel injection accuracy by correcting for any slight tolerances between the crankshaft, timing gears and timing wheel. Timing calibration is normally performed after the following procedures:
1. ECM replacement
2. Speed/timing sensor replacement
3. Timing wheel replacement.
Atmospheric pressure sensor (arrow)
The atmospheric pressure sensor (arrow) is located adjacent to the Engine ECM. The Engine ECM uses the atmospheric pressure sensor as a reference for calculating boost and air filter restriction.
The sensor is also used for derating the engine at high altitudes. The ECM will derate the engine at a rate of 1% per kPa to a maximum of 20%. Derating begins at a specific elevation. The elevation specification can be found in the Technical Marketing Information (TMI) located in the Caterpillar Network. If the Engine ECM detects an atmospheric pressure sensor fault, the ECM will derate the fuel delivery to 20%. If the Engine ECM detects an atmospheric and turbocharger inlet pressure sensor fault at the same time, the ECM will derate the engine to the maximum rate of 40%.
The Engine ECM also uses the atmospheric pressure sensor as a reference when calibrating all the pressure sensors.
The atmospheric pressure sensor is one of the many analog sensors that receive a regulated 5.0 ± .0.5 Volts from the Engine ECM. The atmospheric pressure sensor output signal is a DC Voltage output signal that varies between 0.2 and 4.8 Volts DC with an operating pressure range between 0 and 111 kPa (0 and 15.7 psi).
To check the output signal of analog sensors, connect a multimeter between Pins B and C of the sensor connector. Set the meter to read "DC Volts." The DC Voltage output of the atmospheric pressure sensor should be between 0.2 and 4.8 Volts DC
Engine speed/timing sensor
The engine speed/timing sensor (1) is positioned near the rear of the left camshaft. The sensor signals the speed, direction and position of the camshaft by counting the teeth and measuring the gaps between the teeth on the timing wheel which is mounted on the camshaft.
The engine speed/timing sensor is one of the most important inputs to the Engine ECM. If the Engine ECM does not receive an input signal from the engine speed/timing sensor, the engine will not run.
The engine speed/timing sensor receives a regulated 12.5 ± 1.0 Volts from the Engine ECM. To check the output signal of the speed/timing sensor, connect a multimeter between Pins B and C of the speed/timing sensor connector. Set the meter to read "Frequency." The frequency output of the speed/timing sensor should be approximately:
- Cranking: 23 to 40 Hz
- Low Idle: 140 Hz
- High Idle: 385 Hz
A passive (two wire) engine speed sensor (2) is positioned on top of the flywheel housing. The passive speed sensor uses the passing teeth of the flywheel to provide a frequency output. The passive speed sensor sends the engine speed signal to the Transmission/Chassis ECM and the Brake ECM.
The signal from the passive speed sensor is used for the Automatic Retarder Control (ARC) engine control speed.
The output signal of the passive speed sensor can also be checked by connecting a multimeter between the two pins of the speed sensor connector and setting the meter to read frequency.
NOTE: Turn ON the engine shutdown switch (see Slide No. 23) during the cranking test to prevent the engine from starting. The cranking speed and frequency output will vary depending on weather and machine conditions (battery charge). When viewing engine speed in the ET status screen, cranking speed should be between 100 and 250 rpm
Throttle position sensor (arrow)
The throttle position sensor (arrow) provides the desired throttle position to the Engine ECM. If the Engine ECM detects a fault in the throttle position sensor, the throttle back-up switch (see Slide No. 46) can be used to increase the engine speed to 1300 rpm.
The throttle position sensor receives a regulated 8.0 ± 0.5 Volts from the Engine ECM. The throttle position sensor output signal is a Pulse Width Modulated (PWM) signal that varies with throttle position and is expressed as a percentage between 0 and 100%.
To check the output signal of the throttle position sensor, connect a multimeter between Pins B and C of the throttle position sensor connector. Set the meter to read "Duty Cycle." The duty cycle output of the throttle position sensor should be:
- Low Idle: 16 ± 6%
- High Idle: 85 ± 4%
NOTE: The throttle position sensor setting can be changed in the Engine ECM using the Configuration screen of ET. Two settings are available: 10% to 50% Throttle and 10% to 90% Throttle. The 777D Update truck must be set to the 10% to 90% Throttle setting
Crankcase pressure sensor (arrow)
The crankcase pressure sensor (arrow) is located on the right side of the engine above the engine oil cooler. The crankcase pressure sensor provides an input signal to the Engine ECM. The ECM provides the signal to the Caterpillar Monitoring System, which informs the operator of the crankcase pressure.
High crankcase pressure may be caused by worn piston rings or cylinder liners.
If crankcase pressure exceeds 3.6 kPa (.5 psi) or 14.4 inches of water, a high crankcase pressure event will be logged. No factory password is required to clear this event
EUI fuel injector solenoid (arrow)
Shown is the top of a cylinder head with the valve cover removed. The most important output from the Engine ECM is the Electronic Unit Injection (EUI) solenoid (arrow). One injector is located in each cylinder head. The engine control analyzes all the inputs and sends a signal to the injector solenoid to control engine timing and speed.
Engine timing is determined by controlling the start time that the injector solenoid is energized. Engine speed is determined by controlling the duration that the injector solenoid is energized.
3500B injectors are calibrated during manufacturing for precise injection timing and fuel discharge. After the calibration, a four-digit "E-trim" code number is etched on the injector tappet surface. The E-trim code identifies the injector's performance range.
When the injectors are installed into an engine, the trim code number of each injector is entered into the personality module (software) of the Engine ECM using the ECAP or ET service tool. The software uses the trim code to compensate for the manufacturing variations in the injectors and allows each injector to perform as a nominal injector.
When an injector is serviced, the new injector's trim code should be programmed into the Engine ECM. If the new trim code is not entered, the previous injector's characteristics is used. The engine will not be harmed if the new code is not entered, but the engine will not provide peak performance
Events logged by Engine ECM
The 3500B Engine ECM logs several data events that could cause damage to the engine. Some of the events require factory passwords to clear from the ECM memory. The events logged by the Engine ECM, their maximum derate and their trip points are listed below:
Air filter restriction: Greater than 6.25 kPa (25 in. of water). Maximum derate of 20%. Factory password required.
If the atmospheric and turbo inlet pressure sensors both fail at the same time, a derate of 40% will occur.
Low oil pressure: From less than 44 kPa (6.4 psi) at LOW IDLE to less than 250 kPa (36 psi) at HIGH IDLE. Factory password required.
High coolant temperature: Greater than 107°C (226°F). Factory password required.
Engine overspeed: Greater than 2200 rpm. Factory password required
Additional logged events
Oil filter restriction: Greater than 70 kPa (10 psi). No factory password required. Greater than 200 kPa (29 psi). Factory password required.
Fuel filter restriction: Greater than 138 kPa (20 psi). No factory password required.
Exhaust temperature high: Greater than 750°C (1382°F). Maximum derate of 20%. Factory password required.
Aftercooler coolant temperature high: Greater than 107°C (226°F). Factory password required.
Engine oil level low: No factory password required.
Crankcase pressure high: Greater than 3.6 kPa (.5 psi) or 14.4 inches of water. No factory password required.
Coolant flow low: Factory password required.
User defined shutdown: The customer has the option of installing systems that will shut down the engine if desired. If the installed system sends a ground signal to the Engine ECM at connector
J1 pin 19, a user defined shutdown will occur. Factory password required.
The engine will only shutdown when ground speed is 0 and the parking brake is ENGAGED.
Prelube override: Override the engine oil prelube system with the key start switch. Factory password required.
Engine ECM controls other systems
The Engine ECM also regulates other systems by energizing solenoids or relays. Some of the other systems controlled by the ECM are:
Ether Injection: The Engine ECM will automatically inject ether from the ether cylinders during cranking. The duration of automatic ether injection depends on the jacket water coolant temperature. The duration will vary from 10 to 130 seconds. The operator can also inject ether manually with the ether switch in the cab on the center console (see Slide No. 46). The manual ether injection duration is 5 seconds. Ether will be injected only if the engine coolant temperature is below 10°C (50°F) and engine speed is below 1900 rpm.
Radiator Shutter Control: On trucks that operate in cold weather, shutters can be added in front of the radiator. Installing shutters in front of the radiator allows the engine to warm up to operating temperature quicker. If a truck is equipped with the attachment radiator shutter control, the shutters are controlled by the Engine ECM
Cool Engine Elevated Idle: The Engine ECM provides an elevated engine idle speed of 1300 rpm when the engine coolant temperature is below 60°C (140°F). The rpm is gradually reduced to 1000 rpm between 60°C (140°F) and 71°C (160°F). When the temperature is greater than 71°C (160°F), the engine will operate at low idle (700 rpm).
Increasing the low idle speed helps prevent incomplete combustion and overcooling. To temporarily reduce the elevated idle speed, the operator can release the parking brake or step on the throttle momentarily, and the idle speed will decrease to LOW IDLE for 10 minutes.
Cold Cylinder Cutout: The 3500B engine uses a cold cylinder cutout function to:
- Reduce white exhaust smoke (unburned fuel) after start-up and during extended idling in cold weather
- Minimize the time in Cold Mode
- Reduce the use of ether injection.
After the engine is started and the automatic ether injection system has stopped injecting ether, the Engine ECM will cut out one cylinder at a time to determine which cylinders are firing. The ECM will disable some of the cylinders that are not firing.
The ECM can identify a cylinder which is not firing by monitoring the fuel rate and engine speed during a cylinder cutout. The ECM averages the fuel delivery and analyzes the fuel rate change during a cylinder cutout to determine if the cylinder is firing.
Disabling some of the cylinders during Cold Mode operation will cause the engine to run rough until the coolant temperature increases above the Cold Mode temperature. This condition is normal, but the operator should be aware it exists to prevent unnecessary complaints.
Engine Start Function: The Engine Start function is controlled by the Engine ECM and the Transmission/Chassis ECM. The Engine ECM provides signals to the Transmission/Chassis ECM regarding the engine speed and the condition of the engine pre-lubrication system. The Transmission/Chassis ECM will energize the starter relay only when:
- The shift lever is in NEUTRAL.
- The parking brake is ENGAGED.
- The engine speed is zero rpm.
- The engine pre-lubrication cycle is completed or turned OFF.
NOTE: To protect the starter, the starter is disengaged when the engine rpm is above 300 rpm
Engine oil pre-lubrication
Engine Oil Pre-lubrication: Engine oil pre-lubrication is controlled by the Engine ECM and Transmission/Chassis ECM. The Engine ECM energizes the pre-lubrication pump relay located behind the cab (see Slide No. 53) The relay behind the cab then energizes the pre-lube relay (1) on the front engine mount. The Engine ECM signals the Transmission/Chassis ECM to crank the engine when:
- Engine oil pressure is 3 kPa (.4 psi) or higher.
- The pre-lubrication pump (2) has run for 17 seconds. (If the system times out after 17 seconds, a pre-lubrication time out fault is logged in the Engine ECM.)
- The engine has been running in the last two minutes.
- Coolant temperature is above 50°C (122°F).
The engine oil pre-lubrication system can be bypassed to allow quick starts. To override the pre-lubrication system, turn the key start switch to the CRANK position for a minimum of two seconds. The Transmission/Chassis ECM will begin the pre-lube cycle. While the pre- lube cycle is active, turn the key start switch to the OFF position. Within 10 seconds, turn the key start switch back to the CRANK position. The Transmission/Chassis ECM will energize the starter relay.
If the engine oil pre-lubrication system is bypassed using the above procedure, the Engine ECM will log a pre-lube override event that requires a factory password to clear.
NOTE: The ECAP and ET can enable or disable the pre-lubrication feature in the Engine ECM.
Cooling Systems
The cooling system is divided into two systems. The two systems are the jacket water cooling system and the aftercooler cooling system. When servicing the cooling systems, be sure to drain and fill both systems separately.
The jacket water cooling system uses the cores on the right side of the radiator (approximately 60% of the total capacity). The jacket water cooling system temperature is controlled by temperature regulators (thermostats).
The aftercooler cooling system uses the cores on the left side of the radiator (approximately 40% of the total capacity). The aftercooler cooling system does not have thermostats in the circuit. The coolant flows through the radiator at all times to keep the turbocharged inlet air cool for increased horsepower.
The coolant levels are checked at the radiator top tank. Use the gauges (1) on the top tank to check the coolant level.
Pressure relief valves (2) prevent the cooling systems from becoming over pressurized. The jacket water and the aftercooler cooling systems each have their own relief valve. If a cooling system overheats or if coolant is
leaking from a relief valve, clean or replace the relief valve
Jacket Water Cooling System
The jacket water pump (1) is located on the right side of the engine. The pump draws coolant from the bypass tube (2) until the temperature regulators (thermostats) open. The thermostats are located in the
housing (3) at the top of the bypass tube. When the thermostats are open, coolant flows through the radiator to the water pump inlet
Jacket water coolant temperature sensor (arrow)
cold mode functions such as timing changes, elevated idle, cold cylinder cut-out, ether injection and others.
The Engine ECM provides the signal to the Caterpillar Monitoring System, which informs the operator of the coolant temperature.
If the jacket water cooling system temperature increases above 107°C (226°F), the Engine ECM will log an event that requires a factory password to clear
Coolant flow warning switch
Coolant flows from the jacket water pump, past the coolant flow warning switch (1), and through the various system oil coolers (engine, hoist/converter/brake, and transmission).
The coolant flow switch sends an input signal to the Engine ECM. The Engine ECM provides the input signal to the Caterpillar Monitoring System, which informs the operator of the coolant flow status.
If the ECM detects a low coolant flow condition, a low coolant flow event will be logged. A factory password is required to clear this event.
Jacket water coolant samples can be taken at the Scheduled Oil Sampling (S•O•S) coolant analysis tap (2).
Shown is the right side of the engine. Jacket water coolant flows through the engine oil cooler (1), the transmission oil cooler (2) and the hoist, converter and brake oil cooler (3) to both sides of the engine cylinder block. Coolant flows through the engine block and through the cylinder heads. From the cylinder heads, the coolant flows to the temperature regulators and either goes directly to the water pump through the bypass tube or to the radiator (depending on the temperature of the coolant).
Jacket water cooling circuit
Shown is the jacket water cooling circuit. Coolant flows from the jacket water pump through the coolers to the engine block. Coolant flows through the engine block and the cylinder heads. From the cylinder heads, the coolant flows to the temperature regulators (thermostats) and either goes directly to the water pump through the bypass tube or to the radiator (depending on the temperature of the coolant).
In this illustration and those that follow, the colors used to identify the various pressures in the systems are:
Red - Supply oil/water pressure
Green - Drain or tank oil/water
Red and White Stripes - Reduced supply oil pressure
Brown - Lubrication or cooling pressure
Orange - Pilot or load sensing signal pressure
Blue - Blocked oil
Yellow - Moving components
Purple - Air pressure
Aftercooler Cooling System
The auxiliary (aftercooler) water pump (1) for the aftercooler cooling system is located on the left side of the engine. Coolant enters the aftercooler water pump from the radiator through the tube (2). Coolant flows from the pump to the aftercooler cores through the large tube (3)
Aftercooler coolant samples can be taken at the Scheduled Oil Sampling (S•O•S) coolant analysis tap (4).
Aftercooler
Aftercooler coolant flows from the pump into the front of the aftercooler (1) and exits out the rear. Located in a tube at the rear of the aftercooler is the aftercooler temperature sensor (2). The aftercooler temperature sensor provides an input signal to the Engine ECM. The Engine ECM provides the input signal to the Caterpillar Monitoring
System, which warns the operator if the aftercooler coolant temperature is too high.
If the aftercooler coolant temperature increases above 107°C (226°F), the Engine ECM will log an event that requires a factory password to clear.
Brake oil cooler
Coolant flows through the aftercooler core to the brake oil cooler (1) located at the rear of the engine. Coolant flows through the brake oil cooler to the aftercooler section of the radiator. The aftercooler cooling system does not have temperature regulators (thermostats) in the circuit.
When the service or retarder brakes are ENGAGED, the brake oil cooler diverter valve (2) allows brake cooling oil to flow through the brake oil cooler.
Normally, brake cooling oil is diverted around the cooler and goes directly to the brakes. Diverting oil around the cooler provides lower temperature aftercooler air during high power demands (when climbing a grade with the brakes RELEASED, for example).
If the truck is equipped with the attachment front oil cooled brakes, the brake oil cooler tube will have two ports (3) for brake cooling oil to flow to the front brakes. If the truck is equipped with the standard front caliper disk brakes, the brake oil cooler tube will not have the two ports
Aftercooler cooling circuit
Shown is the aftercooler cooling circuit. Coolant flows from the aftercooler water pump through the aftercooler and the air compressor.
Coolant flows through the aftercooler core to the brake oil cooler located at the rear of the engine.
Coolant then flows through the brake oil cooler to the aftercooler section of the radiator. The aftercooler cooling circuit does not have temperature regulators (thermostats) in the circuit
Engine oil pump And Lubrication System
The engine oil pump is located behind the jacket water pump on the right side of the engine. The pump draws oil from the oil pan through a screen. The relief valve (1) for the lubrication system is located on the pump.
The engine also has a scavenge pump at the rear of the engine to transfer oil from the rear of the oil pan to the main sump.
Oil flows from the pump through an engine oil cooler bypass valve (2) to the engine oil cooler (3). The bypass valve for the engine oil cooler permits oil flow to the system during cold starts when the oil is thick or if the cooler is plugged.
An engine oil level switch (4) provides input signals to the Engine ECM. The Engine ECM provides an input signal to the Caterpillar Monitoring System, which warns the operator when the engine oil level is low and it is unsafe to operate the truck without causing damage to the engine. The ENGINE OIL LEVEL LOW message is a Category 2 or 3 Warning.
Engine oil filters
Oil flows from the engine oil cooler to the oil filters on the left side of the engine. The oil flows through the filters and enters the engine cylinder block to clean, cool and lubricate the internal components and the turbochargers.
The engine has two oil pressure sensors. One sensor is located on each end of the oil filter base. The front sensor (see next slide) measures unfiltered oil pressure. The rear sensor (1) measures filtered oil pressure after the filters. The sensors send input signals to the Engine ECM. The ECM provides the input signal to the Caterpillar Monitoring System, which informs the operator of the engine oil pressure. Used together, the two engine oil pressure sensors inform the operator if the engine oil filters are restricted.
If the engine oil pressure is less than 44 kPa (6.4 psi) at LOW IDLE to less than 250 kPa (36 psi) at HIGH IDLE, the Engine ECM will log an event that requires a factory password to clear.
If the oil filter restriction exceeds 70 kPa (10 psi), a low oil filter restriction event will be logged. No factory password is required to clear this event. If the oil filter restriction exceeds 200 kPa (29 psi), a high oil filter restriction event will be logged. A factory password is required to clear this event.
An oil filter bypass valve is located above each filter in the oil filter base behind the two covers (2). The oil filter bypass valves will open if the oil filter restriction exceeds 203 ± 20 kPa (29 ± 3 psi).
Engine oil S•O•S tap
Shown is the bottom view of the engine oil filter base. Engine oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (1) located on front of the oil filter base.
Also shown is the engine oil pressure sensor (2) that measures the engine oil pressure before the filters.
The oil filter base also has a fitting (3) that can be used to drain the engine oil trapped above the filters. Do not add oil through the fitting because unfiltered oil will enter the engine. Any contamination could cause damage to the engine.
NOTICE
When changing the engine oil filters, drain the oil trapped above the filters through the fitting (3) to prevent spilling the oil. Oil added to the engine through the fitting will go directly to the main oil galleries without going through the engine oil filters. Adding oil to the engine through the fitting may introduce contaminants into the system and cause damage to the engine
Engine oil system
The engine oil pump draws oil from the oil pan through a screen.
The engine also has a scavenge pump at the rear of the engine to transfer oil from the rear of the oil pan to the main sump.
Oil flows from the pump through an engine oil cooler bypass valve to the engine oil cooler. The bypass valve for the engine oil cooler permits oil flow to the system during cold starts when the oil is thick or if the cooler is plugged.
Oil flows from the engine oil cooler to the oil filters. The oil flows through the filters and enters the engine cylinder block to clean, cool and lubricate the internal components and the turbochargers.
Fuel System
The fuel tank is located on the right side of the truck (see Slide No. 13). Fuel is pulled from the tank through the primary fuel filter (arrow) by the fuel transfer pump located on the right side of the engine behind the engine oil pump.
Fuel transfer pump
The fuel transfer pump (1) is located behind the engine oil pump. The fuel transfer pump contains a bypass valve (2) to protect the fuel system components from excessive pressure. The bypass valve setting is higher [approximately 861 kPa (125 psi)] than the setting of the fuel pressure regulator (see Slide No. 87). Fuel flows from the transfer pump through the Engine ECM to the secondary fuel filters located on the left side of the engine.
Secondary fuel filters
The secondary fuel filters and the fuel priming pump (1) are located above the engine oil filters on the left side of the engine. The fuel priming pump is used to fill the filters after they are changed.
Fuel filter restriction is monitored with a fuel filter bypass switch (2) located on the fuel filter base. The fuel filter bypass switch provides an input signal to the Engine ECM. The ECM provides a signal to the Caterpillar Monitoring System, which informs the operator if the secondary fuel filters are restricted.
If fuel filter restriction exceeds 138 kPa (20 psi), a fuel filter restriction event is logged. No factory password is required to clear this event.
Fuel flows from the fuel filter base through the Electronic Unit Injection (EUI) fuel injectors (see Slide No. 66), the fuel pressure regulator and then returns to the fuel tank. The injectors receive 4 1/2 times the amount of fuel needed for injection. The extra fuel is used for cooling.
NOTE: If the fuel system requires priming, it may be necessary to block the fuel return line during priming to force the fuel into the injectors.
Fuel pressure regulator
Fuel flows from the fuel filter base through the steel tubes (1) to the EUI fuel injectors. Return fuel from the injectors flows through the fuel pressure regulator (2) before returning to the fuel tank. Fuel pressure is controlled by the fuel pressure regulator.
Fuel pressure should be between 360 to 725 kPa (52 to 105 psi) at Full Load RPM
Fuel system circuit
Fuel is pulled from the tank through the primary fuel filter by the fuel transfer pump. Fuel flows from the transfer pump through the Engine ECM to the secondary fuel filters.
Fuel flows from the fuel filter base through the fuel injectors in the cylinder heads. Return fuel from the injectors flows through the fuel pressure regulator before returning to the tank.
The fuel priming pump is used to fill the filters after they are changed. If the fuel system requires priming, it may be necessary to block the fuel return line during priming to force the fuel into the injectors
Air Induction and Exhaust System
Shown are the air intake system components. Check the air filter restriction indicators (1). If the yellow pistons are in the red zone (indicating that the filters are plugged), the air filters must be serviced. An air filter restriction indicator is also located on the dash (see Slide No. 47). The alert indicator lights when the filter restriction is approximately 6.2 kPa (25 in. of water).
Located next to the air filter housings are the precleaners. Check the dust valves (2) for plugging. If necessary, disconnect the clamp and open the cover for additional cleaning. Replace the dust valve if the rubber is not flexible.
The dust valve is OPEN when the engine is OFF and closes when the engine is running. The dust valve must be flexible and close when the engine is running or the precleaner will not function properly and the air filters will have a shortened life.
Two filter elements are installed in the filter housings. The large element is the primary element and the small element is the secondary element.
Air intake system tips:
- The primary element can be cleaned a maximum of six times.
- Never clean the secondary element for reuse. Always replace the secondary element.
- Air filter restriction causes black exhaust smoke and low power.
Turbocharger inlet pressure sensor (arrow)
If air filter restriction exceeds 6.25 kPa (25 in. of water), an air filter restriction event will be logged, and the ECM will derate the fuel delivery (maximum derating of 20%) to prevent excessive exhaust temperatures. A factory password is required to clear this event. If the Engine ECM detects a turbocharger inlet pressure sensor fault, the ECM will derate the engine to the maximum rate of 20%. If the Engine ECM detects a turbocharger inlet and atmospheric pressure sensor fault at the same time, the ECM will derate the engine to the maximum rate of 40%.
3508B has two turbochargers
The 3508B engine is equipped with two turbochargers. The turbochargers are driven by the exhaust gas from the cylinders which enters the turbine side (1) of the turbochargers. The exhaust gas flows through the turbochargers, the exhaust piping, and the mufflers.
The clean air from the filters enters the compressor side of the turbochargers. The compressed air from the turbochargers flows to the aftercooler (2). After the air is cooled by the aftercooler, the air flows to the cylinders and combines with the fuel for combustion.
Exhaust temperature sensor (arrow)
Some causes of high exhaust temperature may be faulty injectors, plugged air filters, or a restriction in the turbochargers or the muffler.
If the exhaust temperature is above 750°C (1382°F), the Engine ECM will derate the fuel delivery to prevent excessive exhaust temperatures. The ECM will derate the engine by 2% for each 30 second interval that the exhaust temperature is above 750°C (1382°F) (maximum derate of 20%). The ECM will also log an event that requires a factory password to clear.
Turbo outlet pressure sensor (arrow)
Shown is the turbocharger outlet pressure sensor (arrow). The turbocharger outlet pressure sensor sends an input signal to the Engine ECM. The Engine ECM compares the value of the turbo outlet pressure sensor with the value of the atmospheric pressure sensor and calculates boost pressure.
The best way to check for a power problem is to compare the truck performance with the rimpull charts in the performance handbook (SEBD0340) or the 777D Update Specalog. The truck should be able to climb a grade in the same gear as specified in these two publications.
If an engine power problem is suspected, check boost pressure at full load rpm. If boost pressure is correct at full load rpm, the engine is not the problem and other systems such as the torque converter should be checked.
To check boost pressure at full load rpm, the truck must be operated in FIRST GEAR with the throttle at MAXIMUM and the retarder gradually engaged. Traveling up a grade is best as long as the engine rpm does not fall below the full load rpm specification during the test. Gradually engage the retarder until the full load rpm is displayed. When the full load rpm is displayed, record the boost pressure. If boost pressure is within the specifications at full load rpm, the engine is operating correctly.
Use ET or the Caterpillar Monitoring System display panel to view the engine rpm and boost pressure. The boost and full load rpm specifications are:
Engine ECM set to 746 kW (1000 hp)
* Boost: 221 ± 28 kPa (32 ± 4 psi)
* Full load: 1750 rpm
Engine ECM set to 686 kW (920 hp)
* Boost: 201 ± 28 kPa (29 ± 4 psi)
* Full load: 1750 rpm
Generally, Torque Converter (TC) stall speed (in gear, full throttle, zero ground speed) is used to determine if the engine power is low or a torque converter problem exists. For example, if the engine power is
within specification and the stall speed is high, the torque converter may have a problem (low internal oil pressure, poor internal tolerances or damaged components).
The boost and torque converter stall rpm specifications are: Engine ECM set to 746 kW (1000 hp)
* Boost: 210 ± 28 kPa (30 ± 4 psi)
* Torque Converter Stall: 1540 to 1670 rpm
Engine ECM set to 686 kW (920 hp)
* Boost: 190 ± 28 kPa (28 ± 4 psi)
* Torque Converter Stall: 1540 to 1670 rpm
NOTE: On the 777D Update truck, the horsepower can be changed from 686 kW (920 hp) to 746 kW (1000 hp) by programming the Engine ECM with the ET Service Tool.
Air induction and exhaust system
This schematic shows the flow through the air induction and exhaust system.
The turbochargers are driven by the exhaust gas from the cylinders which enters the turbine side of the turbochargers. The exhaust gas flows through the turbochargers, the exhaust piping, and the mufflers.
The clean air from the filters enters the compressor side of the turbochargers. The compressed air from the turbochargers flows to the aftercooler. After the air is cooled by the aftercooler, the air flows to the cylinders and combines with the fuel for combustion.
THANK YOU FOR VISITED
ENGINE 3508 USE ON 777D OFF-HIGHWAY TRUCK
Reviewed by heri
on
4:23 AM
Rating:
Reviewed by heri
on
4:23 AM
Rating:
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