Post by caleditor on Apr 7, 2012 23:11:48 GMT -6
The EGR valve is an emissions device designed to control NOx. The EGR valve is not a device designed to control spark knock.
The EGR valve controls NOx by lowering the compression camber temperature and pressures by lowering the compression ratio in the engine.
The EGR valve lowers the compression ratio by allowing in an inert gas from the exhaust system.
This inert gas takes up space in the combustion chamber and is compressible and this is how the compression ratio is lowered.
This inert gas is HOT also. Some Vehicles have EGR System coolers that cool the inert gas temperature by a heat exchanger that runs engine coolant through it.
The EGR valve is a device that is a variable. You never know how much inert gas you will get. Carbon build up & exhaust back pressure can have an effect on the amount of inert gas passing through it at the same dwell of open time.
VVT does the same job and it is more predictable. This is one reason EGR valves have been going away and VVT is more common.
An EGR Valve is a device that hurts engine performance
GM
Exhaust Gas Recirculation (EGR) System Description
Purpose
The exhaust gas recirculation (EGR) system is used to lower oxides of nitrogen (NOx) emission levels caused by high combustion temperature. The EGR system does this by decreasing combustion temperature.
Linear EGR Valve
The main element of the system is the linear EGR valve. The EGR valve feeds small amounts of exhaust gas back into the combustion chamber. With the fuel/air mixture diluted by the exhaust gases, combustion temperatures are reduced.
Operation
The linear EGR valve is designed to accurately supply EGR to an engine independent of intake manifold vacuum. The valve controls EGR flow from the exhaust to the intake manifold through an orifice with a PCM controlled pintle. During operation, the PCM controls pintle position by monitoring the pintle position feedback signal. The feedback signal can be monitored with a scan tool as EGR position sensor. The EGR position sensor should always be near the commanded EGR position, Desired EGR Position. The PCM uses information from the following sensors to control the pintle position:
• The engine coolant temperature (ECT) sensor
• The throttle position (TP) sensor
• The mass air flow (MAF)
The linear EGR valve is usually activated under the following conditions:
• Warm engine operation
• Above idle speed
Diagnosis
Too much EGR flow at idle, cruise, or cold operation may cause any of the following conditions to occur:
• Engine stalls after cold start
• Engine stalls during closed throttle conditions
• Vehicle surges during cruise
• Rough idle
• DTC P0300 (misfire detected)
Too little or no EGR flow may allow combustion temperatures to get too high. This could cause the following symptoms:
• Spark knock (detonation)
• Engine overheating
• Emission test failure
• DTC P0401
• Poor fuel economy
EGR flow diagnosis is included in the DTC P0401 diagnostic table. Pintle position error and Control circuit diagnosis is covered in DTCs P0403, P0404, P0405 and P1404.
NOTE: • Poor fuel economy -- This can happen on a vehicle that is calibrated for an EGR Valve and the EGR is disabled without a tune. The calibration has a spark adder table for when the EGR is operating. A good tune will fix that issue just like the how GM did it between a 2002 and 2003 trucks
The EGR valve controls NOx by lowering the compression camber temperature and pressures by lowering the compression ratio in the engine.
The EGR valve lowers the compression ratio by allowing in an inert gas from the exhaust system.
This inert gas takes up space in the combustion chamber and is compressible and this is how the compression ratio is lowered.
This inert gas is HOT also. Some Vehicles have EGR System coolers that cool the inert gas temperature by a heat exchanger that runs engine coolant through it.
The EGR valve is a device that is a variable. You never know how much inert gas you will get. Carbon build up & exhaust back pressure can have an effect on the amount of inert gas passing through it at the same dwell of open time.
VVT does the same job and it is more predictable. This is one reason EGR valves have been going away and VVT is more common.
An EGR Valve is a device that hurts engine performance
GM
Exhaust Gas Recirculation (EGR) System Description
Purpose
The exhaust gas recirculation (EGR) system is used to lower oxides of nitrogen (NOx) emission levels caused by high combustion temperature. The EGR system does this by decreasing combustion temperature.
Linear EGR Valve
The main element of the system is the linear EGR valve. The EGR valve feeds small amounts of exhaust gas back into the combustion chamber. With the fuel/air mixture diluted by the exhaust gases, combustion temperatures are reduced.
Operation
The linear EGR valve is designed to accurately supply EGR to an engine independent of intake manifold vacuum. The valve controls EGR flow from the exhaust to the intake manifold through an orifice with a PCM controlled pintle. During operation, the PCM controls pintle position by monitoring the pintle position feedback signal. The feedback signal can be monitored with a scan tool as EGR position sensor. The EGR position sensor should always be near the commanded EGR position, Desired EGR Position. The PCM uses information from the following sensors to control the pintle position:
• The engine coolant temperature (ECT) sensor
• The throttle position (TP) sensor
• The mass air flow (MAF)
The linear EGR valve is usually activated under the following conditions:
• Warm engine operation
• Above idle speed
Diagnosis
Too much EGR flow at idle, cruise, or cold operation may cause any of the following conditions to occur:
• Engine stalls after cold start
• Engine stalls during closed throttle conditions
• Vehicle surges during cruise
• Rough idle
• DTC P0300 (misfire detected)
Too little or no EGR flow may allow combustion temperatures to get too high. This could cause the following symptoms:
• Spark knock (detonation)
• Engine overheating
• Emission test failure
• DTC P0401
• Poor fuel economy
EGR flow diagnosis is included in the DTC P0401 diagnostic table. Pintle position error and Control circuit diagnosis is covered in DTCs P0403, P0404, P0405 and P1404.
NOTE: • Poor fuel economy -- This can happen on a vehicle that is calibrated for an EGR Valve and the EGR is disabled without a tune. The calibration has a spark adder table for when the EGR is operating. A good tune will fix that issue just like the how GM did it between a 2002 and 2003 trucks
