Can you tell me about "tuning" What is tuning?

Computer recalibration or "tuning" is the process of reprogramming (recalibrating) the factory engine computer to allow the vehicle to operate properly again after modifications have been made as well as optimizing settings to get the most power, driveability, and mileage out of your setup.

Is it worth it to have my baja, sandrail, or dunebuggy tuned?

Factory vehicle ECM's are typically calibrated very conservatively and without (to an extent) performance in mind. Stock vehicles really wake up with minor adjustments to ignition timing, fueling, transmission torque management (if an automatic) and a few other items. These items and more (specific things like speedo fixes from larger tires or gears) are all a part of a Basic tune or a mail order tune. Most off-road vehicles can see a fairly substantial gain with simply retuning for high octane fuel.

Why should I choose tuning rather than a handheld unit?

Our calibrations are custom and tailored to your vehicle and modifications, not a "canned tune". Handhelds typically provide a rather limited range of adjustability compared to custom programming. Even our Basic tunes are one-offs made for your specific application after speaking with you about what can be modified, what you are hoping to gain, and should expect. Custom tuning allows for many changes not possible through handhelds, even for bolt-ons cars. Basic and Mail order tunes are based on many years of street and dyno tuning.

Why do you need a wideband to tune wide-open-throttle?

The oxygen sensors that come stock in your car/truck work really well at maintaining a solid cruising air-fuel ratio (AFR). Once the AFR deviates much above or below this cruise AFR (commonly referred to as stoich), narrow-band (factory) O2 sensors lose their accuracy. Because of this, a wideband is needed to be able to view more of the AFR spectrum; particularly that area around wide-open-throttle which is much richer than cruise.

What is meant by a MAF-based tune or system?

Many cars come from the factory with a device called a Mass Airflow Meter (MAF) that measures the air entering the engine. Even minor mods such as "air-lids" and other "cold air kits" alter the course of flow through the MAF which in turn affects it's calibration. Most of the commanded fueling that a car uses comes directly from this measure of airflow. Most cars will be tuned using the MAF and VE for accuracy of fueling and drivability.

What is meant by a Speed Density tune or system?

Speed-density calibrations use fueling calculations that come solely from static tables referenced against the Manifold Absolute Pressure (MAP) sensor, Intake Air Temp (IAT) sensor, Engine Coolant Temp sensor (ECT) and few other items. This calibration is well suited to more radical setups with very large duration camshafts that can cause reversion issues with a MAF at idle and low engine speed. There are other specific circumstances where this type of calibration can be advantageous.

What is a 2 or 3 bar tune?

Two and three bar tunes are actually special operating systems that are speed density and designed for higher horsepower boosted applications which will exceed internal airflow limits for the MAF within the ECM. These operating systems require the corresponding 2 or 3 bar MAP sensor and allow the ECM to "see" boost (the stock ECM is blind to MAP levels that result from boost) and adjust fueling accordingly. This is particularly important for turbo charged applications which can make boost in many different RPM ranges based on engine load, unlike superchargers whose boost is physically tied to rising engine RPMs.

What does Open Loop and Closed Loop mean?

Closed Loop (CL) refers to a control sub-system in the ECM that allows the engine computer to make adjustments to idle and part-throttle fueling based on feedback from the narrow-band FRONT oxygen sensors. This makes fueling more consistent (in most cases) and helps with highway economy and general drivability. Open Loop (OL) operation means that fueling is calculated and metered from the MAF (unless in speed density where no MAF is used) and other static tables alone with no correction made by the ECM. OL is sometimes desirable in instances such as aiding the operation of a very large camshaft with lots of overlap at lower RPMs. This overlap allows fresh air to escape into the exhaust which "fools" the factory oxygen sensors into thinking that the engine is lean. This can have the effect of causing over fueling at these low RPMs as the ECM attempts to correct a scenario which it perceives to be lean. OL is commonly used on race vehicles and vehicles that use leaded fuel.

What is the AFI Mail Order Tuning you offer?

Mail order tuning is the process of shipping yourECM to us for programming in order to take full advantage of your current setup. We have a worksheet on the site that you fill out. It includes your contact/shipping information as well as a list of all aftermarket modifications as well as a section for any special requests.
Please email us at to get your setup tuned!