Crankcase Ventilation System Description
The crankcase ventilation system is used on diesel engines and is designed to maintain a slightly negative (vacuum) crankcase pressure across the speed range. The system consists of a crankcase depression regulator (CDR) valve, located on the right valve cover and attaching vent hose/pipes to the engine inlet system. The CDR valve is used only to regulate the crankcase pressure between +.249-.996 kPa (1-4 in. of water) depression over the engine speed range. The CDR valve is NOT an oil separator or a crankcase effluent flow regulator. Hence, the CDR valve DOES NOT prevent oil droplets/mist from entering the intake system, nor does the CDR valve affect the engine oil consumption.
The intake manifold vacuum acts against a spring loaded diaphragm in order to control the flow of the crankcase gases. Higher intake vacuum or high intake restriction (e.g., plugged air filter) levels pull the diaphragm closer to the top of the outlet tube. This prevents the vacuum level from getting too high in the crankcase. As the intake vacuum decreases, the spring pushes the diaphragm away from the top of the outlet tube, preventing the crankcase pressure from going positive.
Starting in January 2004, a closed crankcase ventilation system is used to meet new diesel emissions requirements.
Located in both valve rocker arm covers are diaphragms to control the venting of the crankcase gases. As the pressure of the crankcase gases increase, they overcome the spring holding the diaphragm in the closed position. If a vacuum situation arises in the crankcase, the diaphragm closes the port in the valve rocker arm cover. Closing the port will prevent unfiltered air to enter the crankcase.
The crankcase gases travel from the valve rocker arm covers through hoses to a tee, where they enter the turbocharger inlet duct. Because of the use of a closed crankcase ventilation system, it is normal for oil residue to be found on the turbocharger compressor wheel and inside the charge air cooler, pipes, and hoses.
No routine maintenance is required to the crankcase ventilation system.
Exhaust Gas Recirculation (EGR) System Description
The Exhaust Gas Recirculation (EGR) System is used to reduce the amount of nitrogen oxide (NOx) emission levels caused by high combustion temperatures. At temperatures above 1 371°C (2,500°F), oxygen and nitrogen combine to form oxides of nitrogen (NOx). Introducing small amounts of exhaust gas back into the combustion chamber displaces the amount of oxygen entering the engine. With less oxygen in the air/fuel mixture, the combustion pressures are reduced, and as a result, combustion temperatures are decreased, restricting the formation of NOx.
The EGR valve motor is a direct current (DC) stepper motor utilizing a worm gear that extends from the motor to push on the EGR valve stem. The worm gear is not attached to the valve stem, and can only force the valve open. A return spring is used to force the valve closed.
The mass air flow (MAF) sensor signal is used by the engine control module (ECM) to detect the proper amount of EGR flow. One EGR flow test is performed per ignition cycle. The ECM will close the EGR valve for 5 seconds, then open the EGR valve to 100 percent for 5 seconds. The ECM will then calculate the MAF difference and determine if the proper EGR flow has been detected.
Scheme 34
| Callout | Component Name |
|---|---|
| 1 | EGR Valve Position Sensor |
| 2 | EGR Valve Worm Gear |
| 3 | EGR Valve Return Spring |
| 4 | EGR Valve Head |
| 5 | EGR Valve Stem |
| 6 | EGR Valve Motor |
Callouts For EGR Valve
The exhaust gas recirculation (EGR) valve is controlled by the engine control module (ECM) through the EGR motor high control and EGR motor low control circuits. The ECM supplies voltage that is near ignition voltage to the high and low control circuits at all times. This voltage is used by the ECM as a reference voltage during non EGR operation in order to detect circuit failures. The ECM will pulse width modulate (PWM) the low control circuit to ground and an increase in amperage on the high control circuit can be observed with a DMM when the EGR valve is commanded open. A lower pulse width will increase the open position of the valve. In order to close the EGR valve, the ECM will PWM the high control circuit to ground.
When the ignition is turned ON, the ECM will drive the EGR motor worm gear out with just enough force to touch the EGR valve stem. The ECM will do this 3 times in quick succession. This action determines the minimum closed position of the valve and only happens once per ignition cycle. If the valve is prevented from closing all of the way after the minimum closed position is learned, the scan tool EGR Position parameter will not reflect this position until the next ignition cycle. The EGR motor worm gear is not connected to the EGR valve stem and can only push the valve open. The valve is returned to the closed position by a return spring.
The ECM uses the EGR position sensor to determine the position of the EGR valve. The ECM sends a reference voltage through the 5-volt reference circuit to the EGR position sensor. The ECM provides a voltage return path for the sensor through the low reference circuit. A variable voltage signal, based on the EGR valve position, is sent from the sensor to the ECM through the EGR position sensor signal circuit.