How to Tune With Apexi SAFC2

by Alexander Eliot

The A'PEXi SAFC 2 is an electronic fuel-tuning device used to optimize the air-to-fuel ratio in modified engines. Considered a piggyback tuner, the SAFC 2 connects into the engine control unit, or ECU, and modifies the oxygen sensor signal according to your custom settings. The ECU compensates for these settings with an increase or decrease in fuel injection. If you do not have prior knowledge and experience with ECU fuel tuning, have your SAFC 2 tuned by a trained professional. An improper tune can cause substantial damage to vital engine components.

Step 1

Install an air-to-fuel ratio meter in your vehicle. This allows you to monitor the ratio of air and fuel flowing into the engine. Some air-to-fuel ratio meters simply plug into the ECU access port, generally located in the driver's side footwell area. Alternatively, a permanent air-to-fuel ratio gauge can be installed. These require custom splicing into the vehicle wiring harness as well as a custom mounting location.

Step 2

Program the initial settings of the SAFC 2. Use the button controls on the device to navigate to the "NePoint" menu from the main screen. This allows you to set the rpm intervals for fuel tuning, such as one interval at every 1,000 rpm. Navigate back to the main screen, then select the "Th-Point" menu. This allows you to set throttle points for the high-throttle and low-throttle settings. Set the "Hi" option at 80 percent and the "Lo" option at 30 percent.

Step 3

Navigate back to the SAFC 2 main screen. Notice the "Hi-thrtl" and "Lo-thrtl" options. Selecting either option gives you a bar graph with intervals at the rpm values set in the "NePoint" menu. Use the button controls to navigate across rpm intervals, and turn the SAFC 2 adjustment knob clockwise or counterclockwise to add or subtract the fuel correction percentage.

Step 4

Enter baseline fuel-correction values for your vehicle. If your engine is still equipped with the stock fuel injectors, no baseline correction is needed. However, if you are using higher-flowing injectors, check the manufacturer's specifications for the injectors to find out the percentage of increased flow when compared to the stock units. Use this percentage to enter a baseline correction value at all rpm increments on the SAFC 2, on both "Hi-thrtl" and "Lo-thrtl" menus. Since high-flow injectors allow for increased fuel injection, enter this percentage as a negative value to balance the SAFC 2 baseline with your modified injectors.

Step 5

Locate a safe and legal roadway on which you can wind the engine out to its rpm redline. Have a passenger ride along to safely monitor the air-to-fuel ratio meter while you operate the vehicle. Your passenger should take notes of the air-to-fuel ratio value throughout the rpm range if your meter does not have data-logging capabilities, which allow you to save engine data for viewing after a driving session.

Step 6

Accelerate the engine to its rpm redline at full throttle. Full acceleration is necessary to properly load the engine, which allows you to record an accurate air-to-fuel ratio at all rpm values. Have your passenger or data-logging meter record the varying air-to-fuel ratios across the entire rpm band.

Step 7

Park your vehicle and review the recorded air-to-fuel ratio values. Every engine requires a slightly different ratio to optimize performance. The stoichiometric air-to-fuel ratio for internal combustion engines is 14.7-to-1. However, most engines require a richer ratio for maximum performance and reliability. Naturally aspirated engines generally respond well to an approximate ratio of 13.5-to-1, while forced induction engines require a richer tune of approximately 11.5-to-1. If you are unsure of the optimum air-to-fuel value for your specific engine and modifications, speak to a professional tuner who specializes in engines produced by the manufacturer of your vehicle.

Step 8

Compare the recorded air-to-fuel ratio values with the optimum value for your engine. On the SAFC 2 device, navigate to the "Hi-thrtl" menu. Use the adjustment knob to raise and lower fuel-adjustment values at each rpm increment. At increments where you find the air-to-fuel ratio to be greater than optimum value, increase the SAFC 2 fuel-correction value. At increments where the air-to-fuel ratio is lower than the optimum value, decrease the fuel-correction value. Only change the correction value 1 percent or 2 percent at a time to avoid over-correcting.

Step 9

Repeat the tuning process until your air-to-fuel ratio meter records an optimum ratio across the entire rpm band. No matter what, the ratio will fluctuate slightly under acceleration. However, when an efficient tune is achieved, the ratio will remain within a few tenths of the optimum ratio for your vehicle.

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