Closed loop parameters

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Oxygen Sensors

Normally there are two oxygen sensors present in the vehicle.  The primary oxygen sensor is used by the ECU to control closed loop operation.  The secondary oxygen sensor is used to check the performance of the catalytic converter, and also alters the closed loop target lambda in order to provide the optimum mixture for the catalytic converter.


Primary oxygen sensor


For tuning it is recommended to keep the primary oxygen sensor enabled, in order to prevent any tuning differences once switching back to open loop.


Secondary oxygen sensor


The secondary oxygen sensor should be enabled unless running on a race vehicle with no catalytic converter.


WOT determination type


Either the MAP sensor or the throttle (TPS) can be used to determine when to switch from closed loop to open loop.  For most vehicles MAP gives a more consistent switch point.  For forced induction vehicles, MAP must be used.


MAP WOT determination


This table contains the manifold pressure used to determine WOT (wide open throttle = high load).  At WOT the ECU will switch to open loop and use the WOT lambda adjustment tables.


TPS WOT determination



Two tables are used to determine the closed to open loop switch point based on throttle position.  The high table contains the switch point from closed to open loop.  The low table contains the open to closed loop switch point.  Normally the low table values should be a few degrees lower than the high table to prevent oscillation between open and closed loop.


LAF voltage to lambda


This table contains the conversion from the stock wideband oxygen sensor to lambda (air/fuel).


Also see Wideband lambda interface


Closed Loop Target Lambda

This controls the target lambda (air/fuel ratio) when the vehicle is running in closed loop.  A combination of  tables is used the set the target lambda, based on temperature and load.


The target lambda used is the richer (lower lambda or air/fuel ratio) of the 'Closed loop target lambda', 'Closed loop target lambda limit' and one of the 'Closed loop target lambda load' tables.  The transition from low to high load is at approx 50 kPa.


Warning: Running leaner than stoichiometric (lambda 1, approx 14.6:1) will increase exhaust gas temperatures.  For this reason it is not recommend to change these parameters for vehicles with catalysts.


Fuel Trim Min/Max

This controls the minimum and maximum percentage of short term and long term fuel trim the ECU compensates for while in closed loop.


The AF learned value minimum and maximum control the range for the stored short term fuel trim value.  This value is calculated from the average short term fuel trim over 20 minutes, and is used by the ECU when switching from open loop to closed loop as a starting short term fuel trim.