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SMT6 Developers Manual - Fuel Modifications


Perfect Power Online Manuals.


Support for your SMT6 Unit.


Most engines operate in "closed loop" oxygen (lambda) control up to a certain RPM and a certain throttle position for partial power. More modern engines run closed loop at full power with a different (wide band) oxygen sensor.





This is required if tuning is needed in the "closed loop" operating mode of the engine. The oxygen sensor has a voltage output of 0.2 to 1.00 Volts, which can be "tuned" up or down as required. Some ECU's respond slowly to the input, some are fast! Locate sensor, and trace wire to the ECU. Measure with voltmeter while engine idles : it should read 0.5 Volts, or fluctuate up/down around 0.5 Volts.


Two functional different connections are possible .


  • Run the Lambda signal through the SMT6 as any other analog signal : INPUT@AIN, pin 6, blue, OUTPUT@AOUT, pin 18, violet. This requires the use of the analog limits to make clever use of the Lambda range.
  • Use the Lambda display output input as the analog source (Lambda Tune : Y). The output is on AOUT, but the input is on pin 22, black/brown. The Lambda display is from the input. In this mode the SMT6 makes use of the increased Lambda resolution and a special algorithm (nonlinear) is used for tuning. This method requires no analog limit.





This is required for tuning outside the closed loop-operating mode of the ECU.


There are THREE kinds of AIRFLOW meters :

  • The voltage output meter. Output is from 0.5  -7.5 Volt according to airflow.
  • The frequency output meter. Output is a frequency according to airflow.
  • The current output meter. The current changes according to airflow.



Locate airflow meter and output wire. Then measure with scope.

If frequency meter : use MODE=10
If voltage meter : use any MODE.



If a wire is not found which changes with airflow, then it may be a current meter type. Place a  100-470 ohm in SERIES with the wire (from ECU wiring diagram) and measure the voltage ACROSS the resistor. If it changes with airflow, then it is a current meter. Use any MODE.





This is required for tuning outside the closed loop operation of the ECU. The output of a manifold pressure sensor is normally 0.2 - 4.8 volts with 5 Volts  feed. This range corresponds to the full (vacuum to atmospheric or boost) pressure range.


The SMT6 can tune the AMP (analog) in any mode.





This is required for tuning outside the closed loop operations of the ECU and when the  ECU fuel is limited by fuel pressure, injector size, and mapping or otherwise. It is recommended for large power increases as a result of supercharging or fitting a  turbo.


An Extra Injector (up to 6 x 16 ohms) is placed in the manifold and activated under the (F2) injection map from the SMT6.





Most ECU's enrich the fuel mixture and advance the timing for cold engines. The engine temperature sensor must be routed through the SMT6. Before doing that, check if the sensor requires a "pull-up" by measuring the sensor output with the ECU connected, and without. If the voltage drops to zero, then a pull-up is required (to +5V, or to +12V) which restores the voltage to the level it was with the ECU connected. Some ECU's detect the low engine temperature after 30 minutes as  "illogical" and indicate a "service fault".





Some engines don't have air temperature sensors and rely on warmed up manifolds and other mechanical means to keep the air at a relative constant temperature. Turbo charged and inter-cooled engines will have an air temperature sensor because the temperature varies by a considerate amount. Most ECU's make the mixture leaner at higher temperatures, because the air density is less. This can be used for tuning. The air temperature sensor may require a pull-up as above.





Only analog signals such as Lambda, airflow meter and manifold pressure signals  are tuned. The tuning is done via the analog map AND the engine temperature.


In most cases the engine is "leaned out" to the absolute extreme under control of the engine temperature.


Special application notes are available. See : Lambda Tuning. A word of caution :


  • Do not expect too much. It is possible to "lean out" engines, and to conserve fuel.
  • The gains may be in the 5-20% range.


However, older engines can be modernized and made environmentally friendly.