SMART TUNER SMT8 - FUEL TUNING VIA AFM OR MAP

Introduction

This application note describes the methods of tuning the air fuel ratio of the engine via the Air Flow Meter or MAP sensor.

Purpose

Why would you want to re-tune the engine Air Fuel Ratio? From the continual use of an engine the combustion efficiencies decrease and it could be found that the engine starts using more fuel than before. As most factory fitted management systems needed specialized computer equipment to adjust the ratio and are no longer available, tuning the engine via a Piggy-Back becomes the only option.

SMT8 Analog Wiring

Using the SMT8, you can now tune the Air Fuel Ratio (AFR). To do this you would need to control the voltage from the air flow meter or the MAP sensor, which is normally in a range from 0-5 Volts. The incoming voltage is wired into the Analog channel on the Ana#1 in and then back to the OEM ECU on the ANA#1 out.

 

 

SMT8 Analog Setup

 

The Analog voltage has three parameters in the "Shift F1" map, they are the "An1 Upper Limit", "An1 Lower Limit" voltages and the "Analog#1 Offset %" percentage. The Upper limit clamps the maximum voltage that would be return to the OEM ECU, this works the same for the Lower Limit. The offset percentage will increase or decrease the entire Analog #1 map, so if the engine is too rich across the complete rev range then there would be a negative value entered to lean the engine out.

SMT8 Analog Mapping

The SMT8 has 2 Analog input channels and two separate maps. Both use a main map of 384-entry sites, which is added to two (24-row) side maps for engine and air temperature map and then multiplied by the (24-row) manifold pressure side map. The map sites are selected by the throttle position (or any other load signal) and the RPM. For this example we will only be using the Analog #1.

 

 

 

 

 

 Testing if you have control of the fueling is simply done by entering a large number into the green cell in the main map during idle and confirming that the engine's pitch changes. The mapping calculation is as follows :

 

A1OUT	=	AN1IN
		+- ANA1 MAP
		+- AN1 ENGT
		+- AN1 AIRT
		X AN1 AMP

 

 

Conclusion

Most of us spend 90% of the time while driving a car "cruising" due to speed and traffic restrictions. The SMT8 is the ideal tool to improve the cruising performance, while enhancing the power output at full throttle when overtaking.