Exhaust Variable Valve - Using the valve lap to create an EGR effect, wow that turns me on....

 

THEORY OF OPERATION

Exhaust variable valve timing and EGR control mode (sub-modes) –are modes used explicitly for the reduction of NOx gasses. The different oxides of nitrogen form at a specific A/F ratio of about Lambda 1.08 to 1.12 (slightly lean) and very high combustion temperatures. Engineers have addressed this problem with the EGR or engine gas re-circulation system. A small amount of exhaust gas is re-introduced into the exhaust chamber in order to inhibit and lower combustion chamber temperatures. The EGR operating mode can be achieved through various means, as with an EGR valve, fixed exhaust valve overlap and variable exhaust valve timing. With the EGR valve method, a vacuum or electronic EGR valve is used for exhaust gas re-circulation. This system could be either with feedback loop (DPFE, EVP, Temperature sensing or MAP sensing) or without it. The valve overlap gas re-circulation method system simply leaves the intake and exhaust valves open at the same time, which forces some exhaust gas to re-enter the combustion chamber. If the valve train is fixed, then the amount of re-circulated gas is determined by the mechanical position of the exhaust camshaft lobes. This is all taken into account during the engine design phase. The drawback to this system is that EGR operation should be very minimal or non-existent at idle speeds, which this system can not control. With variable valve timing, the ECM controls the amount of EGR by means of a duty-cycle operated oil pressure solenoid. The amount of EGR is determined by the duty-cycle commanded by the ECM. This system can also be of the open or closed feedback type. With a close-feedback system, a cam position sensor (potentiometer) is used to monitor the exhaust camshaft position and calculated into degrees, by the ECM. The ECM is then constantly monitoring the cam position and adjusting the solenoid according to the look-up tables, stored in the ECM’s ROM memory. Any operational difference between the desired and actual cam phase is perceived as a camshaft error and reported by an ECM trouble code (EGR flow error). It is also good to point out that the exhaust valve timing control is not to be confused with its cousin, the broader variable valve timing strategy. These two modes or ECM strategies both employ variable valve timing, but only the exhaust cam is used to control EGR flow. The newer systems also use the intake cam for performance and torque management. However, regardless of what type of system used, the ECM always uses the RPM signal (engine speed) and the calculated engine load factor as the two main inputs for EGR operation. The engine load is calculated from the various sensors in the fuel control system. And any erroneous reading from one of these sensors will also derail the EGR operation. Just remember never to engage in code repair and simply change a component because there is a code for it. A careful analysis before a diagnostic decision is made is always preferable.

The knowledge of the different ECM modes of operation is an integral part of the overall foundation that each technician should have. The technician should always ask him/herself the very basic question of diagnostics “ what is the ECM seeing that’s causing it to do what it’s doing ? ”. From this answer and the information gathered in the technician’s toolbox of knowledge, a proper diagnostics path can be taken. This section was intended to provide a basic knowledge of the complexities of ECM programming modes.

 

Hit Counter

Ask DIY-Car-Doctor

Watch our Videos

More Services

 

Sensors                 O2-Sensor                  APP-Sensor                CAM-Sensor               CRK-Sensor               ECT-Sensor               IAT-Sensor                 Knock-Sensor              MAF-Sensor                MAP-Sensor                TPS-Sensor                 VSS-Sensor                FRP-Sensor                AFR-Sensor              

Actuators               Fuel-Injectors            Ignition-Coil           Leak-Detection Pump  GM-Series Alternator   Idle-Control Valve      EGR-System            EVAP-System      

Repair Strategies Current-Ramping      Lack of Power           Fuel-Flow Volume     Ignition Waveform       Ignition Testing          A/F Ratio Diagnosis    Minimum Air Rate      No Fuel-Pressure       No Injector Pulse      No-Start/No-Spark     General No-Start      

ECM/PCM Modes Cranking Enrichment   Warm-up Cycle         Open-Loop            Closed-Loop            Accel. Enrichment Deceleration Leaning   Idle Control             Low-Voltage Correction Clear Flood Mode     Selective Inj. Cut-Off   Limp-In Mode           Exhaust Variable Valve

 OBD-2 Codes

Generic DTCs            GM Cars DTCs           GM Truck DTCs        Ford DTCs                  Ford Trucks DTCs        Dodge DTCs                BMW DTCs                 Honda/Acura DTCs       Hyundai DTCs              Isuzu DTCs                  Jaguar DTCs                Kia DTCs                     Land Rover DTCs          Mazda DTCs                Mercedes DTCs           Mitsubishi DTCs           Nissan/Infinity DTCs     Saab DTCs                  Subaru DTCs               Toyota DTCs                Volvo DTCs                  VW/Audi DTCs        

 Code Setting Criteria

Dodge CSC                 Ford CSC                    GM CSC                     Honda/Acura CSC        Hyundai CSC               Isuzu CSC                   Kia CSC                      Mazda CSC                 Mitsubishi CSC            Nissan/Infinity CSC      Subaru CSC                Toyota/Lexus CSC

SRS Airbag DTC

GM SRS Airbag Code   GM Truck SRS Code    Ford SRS Airbag Code  Ford Truck SRS Code   Dodge SRS Code        Dodge Truck SRS Code Acura/Honda SRS Code Isuzu SRS Codes         Mazda SRS Codes        Subaru SRS Codes Infinity/Nissan SRS       Kia SRS Codes     Hyundai SRS Codes     Mitsubishi SRS Codes Lexus/Toyota SRS

How to Get SRS Codes

Retrieving Dodge SRS   Retrieving Ford SRS     Retrieving GM SRS      Retrieving Honda SRS   Hyundai/Kia/Mitsu SRS Isuzu/Mazda/Subaru     Retrieving Toyota SRS  Nissan/Infinity SRS

SRS-Airbag Repair Guide

Deleting SRS Codes   Dodge SRS Location       Dodge SRS Operation     Ford SRS Location          Ford SRS Operation        GM SRS Location            GM SRS Operation           Honda SRS Location       Honda SRS Operation     Isuzu/Mazda/Suba Loc.   Isuzu/Mazda/Suba Ope Kia/Hyun/Mitsu Location Kia/Hyun/Mitsu Oper.       Nissan/Infinity Location   Nissan/Infinity Operation Toyota/Lexus Location    Toyota/Lexus Operation 

T

copyright 2011 Mandy Concepcion, Automotive Diagnostics and Publishing