XMS5 - SELF TUNING APPLICATION
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Perfect Power Application Notes. |
Application Note - AN 5 |
This note describes the PRS self-tuning process, which is achieved with CLOSED LOOP LAMBDA operation.
Explanation of Lambda Measuring
AIR/FUEL RATIO (AFR)

These LAMBDA sensors are used in different configurations :
- With/Without Heater
- Single/Two Wire Sensor
- Narrow/Wide Band Characteristic
The XMS5B unit can only work with the wide band lambda probes, which are wired, directly into it.
Problems with Lambda Sensors
Position in the Manifold
It is advisable to install the sensor as close as possible to the engine. That is the point where the branches meet. If extremely long branches are used, then it may be better to install the probe at a "2 into 1" junction. A temporary installation in the tail pipe is not recommended.
Gas Velocity
Sometimes the gas velocity cools the sensor head, and the result is a "LEAN" reading. This can be adverted by placing the sensor in a "sheltered" position, or by placing a little deflection plate in front of the sensor head. Make sure it does not obstruct the exhaust gas flow.
Electrical Interference
If the sensor element is grounded to the case, then the XMS5 reads engine "noise" from the alternator, or ignition "noise". This makes the reading useless!
Tuning with Lambda
LAMBDA TARGETS : | 384, throttle dependent |
LAMBDA LIMITS : | 16, the max amount by which the lambda probe can change the fuel |

XMS5 Operation
Practical Operation
Very often we are asked the question : " Why is long term trim map made?" "Why not let the Lambda automatically tune?". Early software versions had this feature, but it was not practical, for the following reasons :
- It was difficult to tune yourself our of a total wrong map point
- There is no difference between a very lean engine, and a "cool" or malfunctioning lambda probe.
- Some map points should be "rich" and others "lean" in the same column.
- It removed the human touch from the tuning process.
We at Perfect Power believe that it is the best possible "automated" tuning process, although you may conclude that it is "semi-automatic".