Perfect Power Application Notes.


This note describes ways to adapt different airflow (air mass meters) to a stock ECU via a SMART TUNER SMT8-L.



The airflow into an engine has to be metered so that the ECU can supply the correct fuel. Very often the stock-metering device is no good, too small, or too expensive, and it must be replaced with a different unit, which leads to all kind of problems. The following different air flow meters exist :

Analog Output Hot Wire System

The air flows over a heated wire and cools it. The amount of cooling is proportional to the airflow, and the output is a "DC VOLTAGE" describing the amount of air. This unit is also called an AIR MASS METER, because it recognizes the air density.
SMT8-L Piggy-Back Unit - Analog Output Hot Wire System
Looking at the signal while the airflow changes using an oscilloscope would look something like this.
SMT8-L Piggy-Back Unit - Airflow Changes on Oscilloscope


Frequency Output Hot Wire System

 Same as above, but the output is a frequency, which describes the amount of airflow. This device is also called an AIR MASS METER.

An oscilloscope display of a frequency signal.


SMT8-L Piggy-Back Unit - Frequency Output Hot Wire System



Analog Output Mechanical Door System

A trap door is placed in the air stream, and the flowing air opens the door against a spring. The degree of door movement is measured via a potentiometer and results in an analog output voltage, which is proportional to the airflow. This system relies on the spring tension and mechanical "DAMPENING", because it OVER SWINGS at acceleration.
SMT8-L Piggy-Back Unit - Analog Output Mechanical Door System

Absolute Manifold Pressure Sensor (Map, or AMP)

This device measures the manifold pressure after the butterfly. The output is an analog voltage. It is not a direct measurement of the airflow, but indirectly the engine load can be determined from it, and the ECU can adjut the fuel accordingly.
SMT8-L Piggy-Back Unit - Absolute Manifold Pressure Sensor (MAP, AMP)


If your ECU requires an ANALOG airflow signal, then you need an ANALOG airflow meter. NOT the same make, but analog!
SMT8-L Piggy-Back Unit - Restrictions
If your ECU requires a DIGITAL (FREQUENCY) airflow signal, then you can replace the existing metering device with a frequency meter ONLY.


The SMT8-L cannot convert an analog signal to a digital (frequency) one, or a digital signal to an analog one. (These features may be added later). This analog-to-analog adaptation or frequency-to-frequency adaptation is a standard feature of the SMART TUNER range.