• ETHER INJECTION
• RADIATOR SHUTTER CONTROL
• COLD CYLINDER CUTOUT
• ENGINE START FUNCTION
• ENGINE OIL PRE-LUBRICATION
• VARIABLE SPEED FAN CONTROL
• ENGINE OIL RENEWAL SYSTEM
• EXHAUST BYPASS AT HIGH BOOST
The engine ECM also regulates other systems by energizing solenoids or relays. Some of the other systems controlled by the ECM are:
Ether Injection: Ether injection is controlled by the engine ECM or manually. The engine ECM will energize the ether injection relay only if:
- The coolant temperature is below 10°C (50°F).
- Engine speed is below 1200 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.
• Engine ECM controls other systems
• Ether injection
• Radiator shutter control
function to reduce white exhaust smoke after start-up and during extended idling in cold weather.
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 cut-out. The ECM averages the fuel delivery and analyzes the fuel rate change during a cylinder cut-out 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 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 ADEM II and the Electronic Programmable Transmission Control (EPTC II). The engine ECM provides signals to the EPTC II regarding the engine speed and the condition of the engine pre-lubrication system.
The EPTC II will energize the starter relay only when:
- The shift lever is in NEUTRAL.
- The parking brake is ENGAGED.
- The engine speed is 0 rpm.
- The engine pre-lubrication cycle is complete or turned OFF.
NOTE: To protect the starter, the starter is disengaged when the engine rpm is above 300 rpm.
INSTRUCTOR NOTE: The remaining improvements are described in the slides that follow.
• Engine runs rough during cold mode
• Engine start function
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1
Engine Oil Pre-lubrication: Engine oil pre-lubrication is controlled by the ADEM II and EPTC II. The EPTC II signals the ADEM II when to energize the pre-lubrication pump relay (1). The ADEM II signals EPTC II to crank the engine when:
- Engine oil pressure is 27 kPa (5 psi) or higher.
- The pre-lubrication pump (2) has run for 15 seconds. (If the system times out after 15 seconds, a pre-lubrication fault is logged in the ADEM II.)
- The engine has been running in the last 2 minutes.
- Coolant temperature is above 50°C (122°F).
NOTE: The ECAP and ET can enable or disable the pre-lubrication feature in the ADEM II. On some trucks, the pre-lubrication pump is located near the right front of the engine.
• Engine oil pre-lubrication
1. Pre-lubrication pump relay
2. Pre-lubrication pump
• Variable speed fan
Variable Speed Fan Control: If the engine is equipped with a variable speed fan, the engine ECM regulates the fan speed. Fan speed varies according to the temperature of the engine. The ECM sends a signal to the variable speed fan control solenoid valve (1) and engine oil pressure engages a clutch as needed to change the speed of the fan.
The jacket water coolant temperature sensor (2) is located in the jacket water temperature regulator (thermostat) housing. The ECM uses the coolant temperature sensor information as the main parameter to control the fan speed. The aftercooler temperature sensors, air conditioner
pressure sensor and brake cooling oil temperature sensors are also used as inputs to determine the required fan speed. A speed sensor (not shown) is located behind the fan pulley and informs the ECM of the current fan speed.
The variable speed fan feature can be turned off using the ECAP or ET service tool. Turning off the variable speed fan feature will set the fan speed at MAXIMUM rpm. Disconnecting the air conditioning
compressor switch will also signal the ECM to set the fan speed at MAXIMUM rpm.
The turbocharger outlet pressure sensor (3) sends an input signal to the ECM. The ECM compares the value of the turbo outlet pressure sensor with the value of the atmospheric pressure sensor and calculates boost pressure.
INSTRUCTOR NOTE: For more information on the variable speed fan, refer to the Service Manual "Variable Speed Fan Clutch"
(Form SENR8603).
1. Fan control solenoid valve
• Fan speed sensor (not shown)
• Fan speed overrides
3. Turbo outlet pressure sensor 2. Jacket water coolant
temperature sensor
• Engine oil renewal system components:
1. Oil filter 2. Oil renewal
solenoid 3. Fuel pressure
regulator
• Oil mixes with fuel in fuel tank
53 1
3
2
Engine Oil Renewal System: Located on the right side of the engine are the components of the engine oil renewal system. Engine oil flows from the engine block through an oil filter (1) to the engine oil renewal
solenoid (2). A small amount of oil flows from the engine oil renewal solenoid into the return side of the fuel pressure regulator (3). The engine oil returns to the fuel tank with the return fuel.
The engine oil mixes with the fuel in the tank and flows with the fuel to the EUI injectors to be burned.
When the engine oil renewal system is used, the operator must pay close attention to the ADD OIL message that the VIMS provides to the operator when makeup oil must be added (see Slide No. 54).
The oil does not have to be changed when using the engine oil renewal system. When the engine oil renewal system is used, the engine oil filters, the engine oil renewal system filter, the primary fuel filter and the secondary fuel filters must all be changed at 500 hour intervals.
Engine oil samples must be taken regularly to ensure that the soot level of the engine oil is in a safe operating range.
• Sample engine oil to check soot level
by engine ECM
• Engine oil renewal system parameters
renewal solenoid. Several parameters must be met before the ECM will allow the injection of oil through the engine oil renewal system. The parameters that must be met are:
- Fuel position is greater than 10.
- Engine rpm is between 1300 and 1850 rpm.
- Jacket water temperature is between 63°C (145°F) and 107°C (225°F).
- Oil filter differential pressure at high idle with warm oil is less than 70 kPa (10 psi).
- Fuel filter differential pressure is less than 140 kPa (20 psi).
- Engine oil level switches are sending a valid signal to the ADEM II control.
- Engine has been running more than five minutes.
The engine oil renewal system can be turned ON or OFF with the ECAP or ET service tool. The amount of oil injected can also be adjusted by programming the ECM with the ECAP or ET service tool. The factory setting shown in the service tool is "0" and is equivalent to a 0.5% oil to fuel ratio. The ratio can be changed with the service tool from minus 50 (-50) to plus 50 (+50), which is equivalent to 0.25% to 0.75% oil to fuel ratios.
• Oil renewal adjusted with ECAP or ET
54 1
2
The engine oil level switches (1 and 2) provide input signals to the engine ECM. The ECM provides an input signal to the VIMS which informs the operator of the engine oil level.
If the truck is equipped with the engine oil renewal system attachment, the upper oil level switch (1) will tell the operator when makeup oil must be added. The ADD ENG OIL message is a Category 1 Warning.
The lower oil level switch (2) will tell the operator when the engine oil level is low and it is unsafe to operate the truck without causing damage to the engine. The ENG OIL LEVEL LOW message is a Category 2 or 3 Warning.
If the engine ECM detects a low oil level condition (oil level below the lower switch), the ECM will log a low oil level event. No factory password is required to clear this event.
1. Add engine oil level switch
2. Engine oil level low switch
• Low oil level event
1. Exhaust bypass valve
55
1
2
Exhaust Bypass Control: An exhaust bypass (wastegate) valve (1) prevents excessive boost pressure by diverting exhaust gasses away from the turbochargers. The bypass valve is controlled by the engine ECM.
Brake system air pressure is reduced to 380 kPa (55 psi) by a valve located outside the right rear of the cab and is supplied to the wastegate solenoid valve (2). If boost pressure exceeds a predetermined value, the ECM will open the wastegate solenoid and send air pressure to open the exhaust bypass valve. When the exhaust bypass valve is open, exhaust at the turbine side of the turbochargers is diverted through the muffler.
Diverting the turbine exhaust pressure decreases the speed of the turbochargers which reduces the boost pressure to the cylinders.
The wastegate solenoid valve can be controlled with the ECAP or ET service tool for diagnostic purposes. Connect a multimeter to the wastegate solenoid and set the meter to read DUTY CYCLE. Using the service tool, override the wastegate solenoid valve and use the multimeter to measure the corresponding duty cycle.
If the actual boost pressure is 20 kPa (3 psi) higher than the desired boost pressure calculated by the ECM, a high boost pressure event will be logged. If the actual boost pressure is 30 kPa (4 psi) lower than the desired boost pressure calculated by the ECM, a low boost pressure event will be logged. If the ECM detects a high or low boost condition, the ECM will derate the fuel delivery (maximum derating of 10%) to prevent damage to the engine.
2. Wastegate solenoid valve
- Controlled by engine ECM
• Engine wastegate solenoid checked with ECAP or ET
• Boost pressure events
1. Cooling system shunt tank
• Engine cooling systems:
- Jacket water cooling system
The 793C is equipped with a shunt tank (1) to increase the cooling
capacity. The shunt tank provides a positive pressure at the coolant pump inlets to prevent cavitation during high flow conditions.
The cooling system is divided into two systems. The two systems are the jacket water cooling system and the aftercooler cooling system. The only connection between these two systems is a small hole in the separator plate in the shunt tank. The small hole in the shunt tank prevents a reduction of coolant from either of the two systems if leakage occurs in one of the separator plates in the radiator top or bottom tank. When servicing the cooling systems, be sure to drain and fill both systems separately.
The coolant levels are checked at the shunt tank. Use the gauges (2) on top of the shunt tank to check the coolant level.
A coolant level sensor (3) is located on each side of the shunt tank to monitor the coolant level of both cooling systems (guard removed for viewing sensor). The coolant level sensors provide input signals to the VIMS which informs the operator of the engine coolant levels.
Pressure relief valves (4) prevent the cooling systems from becoming over pressurized.
4. Pressure relief valves
3. Coolant level sensor 2. Coolant level gauges
57
The jacket water cooling system uses 17 of the 30 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 13 of the 30 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.
• Aftercooler cooling system
• Jacket water cooling system
1. Jacket water pump 2. Bypass tube 3. Jacket water
thermostat housing
58 2
1
3
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.
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.
• High coolant temperature event
• Coolant flow warning switch (arrow)
59
Coolant flows from the jacket water pump, past the coolant flow warning switch (arrow), and through the various system oil coolers (engine, torque converter/transmission and rear brake).
The coolant flow switch sends an input signal to the engine ECM. The ECM provides the input signal to the VIMS 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.
• Low coolant flow event
1. Engine oil cooler 2. Torque converter/
transmission oil cooler
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Shown is the right side of the engine. The engine oil cooler (1) and the torque converter and transmission oil cooler (2) are visible in this view.
The coolant flows through these coolers to the rear brake oil coolers located on the outside right frame.
• Rear brake oil coolers (arrow)
61
Jacket water coolant flows from the rear brake oil coolers (arrow) 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 returns 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).
62
• Jacket water cooling system circuit