Tuning EFI Systems - EFI Basics - Car Craft Magazine

Tuning EFI
In the '80s through early '90s, performance enthusiasts shunned factory EFI systems because they were difficult and cumbersome to use since any tuning change required burning a new chip. The big advantage of even the earliest aftermarket EFI systems was that they were designed to be quickly and easily modified. All you needed was a laptop, a little bit of computer savvy, and tuning skill. By the mid '90s, the factory realized the advantage of instantly reprogramming their ECMs by merely plugging into the on-board assembly-line diagnostic link (ALDL) port located under the dash. This change to electronically erasable chips (EE-PROM) fueled a move in the aftermarket to the now-famous GM-based HP Tuner and EFI Live programs along with the Ford-compatible TwEECer software packages, which allow enthusiasts to take maximum advantage of the highly sophisticated engine control offered by the factory systems.

Most aftermarket EFI systems use OE-style sensors. This TPS sensor is mounted on the throttle linkage of an Accel four-barrel throttle body. The TPS sensor converts throttle movement into a voltage signal to tell the computer not only the location of the throttle, but also its rate of change of position.
Most aftermarket EFI systems use OE-style sensors. This TPS sensor is mounted on the throt
Early aftermarket EFI systems relied on narrow-band oxygen sensors that were only accurate at 14.7:1. Most new EFI systems now integrate wide-band oxygen sensor capability to allow tuning the air/fuel mixture across a much wider range, from 11:1 to 16:1 and leaner. The eMS-Pro EFI system, for example, uses Innovate Motorsports' wide-band oxygen sensor for accurate air/fuel ratio data.
Early aftermarket EFI systems relied on narrow-band oxygen sensors that were only accurate
There are two types of MAF sensors: hot-wire and hot-film sensors. In both cases, the wire or film is placed in the incoming air path. The computer measures and adjusts the amount of voltage required to maintain a given resistance in the wire or film. As the volume of air increases, it cools the sensor, requiring more voltage to maintain a given temperature.
There are two types of MAF sensors: hot-wire and hot-film sensors. In both cases, the wire

This has driven the aftermarket to offer better and more sophisticated systems for true high-performance applications. For example, most aftermarket systems such as ACCEL's DFI, Comp's FAST, and BigStuff3, to name a few, offer options such as nitrous control as an integral part of the tuning structure. This option allows the tuner to control not only several stages of nitrous but also when and how much fuel is added, along with intricate control over how much timing is retarded at each stage. Plus, a few of these units, such as John Meaney's BigStuff3 Gen3 PRO SEFI box, offer mastery over both the engine and an electronic overdrive automatic transmission. If you're a control freak, it doesn't get much better than this because these boxes give you total control over sequential fuel injection where you can make changes in fuel delivery to individual cylinders with feedback from a pair of wide-band oxygen sensors. Plus, they can also drive up to 16 low-impedance fuel injectors. That's serious power. The BigStuff3 SEFI (sequential) box, for example, can also control a complete distributorless ignition system, which allows spark calibrations for individual cylinders.

Another excellent sensor that can actually help save your engine is a knock sensor. It signals the ECM when the engine begins to suffer from detonation and can pull timing back to prevent engine damage. For example, the FAST XFI system offers electronic spark control (ESC) that is tunable not only for how much timing is retarded, but also how quickly the reduction comes in as well as the decay rate of the retard.
Another excellent sensor that can actually help save your engine is a knock sensor. It sig
The big knock on EFI is the required investment in an expensive laptop computer in order to tune the system. A laptop is useful for many reasons beyond just EFI tuning, and their prices have never been cheaper. But if that's your roadblock to getting into EFI, everyone has a buddy with a laptop.
The big knock on EFI is the required investment in an expensive laptop computer in order t

Aftermarket EFI Maps
The big argument against aftermarket fuel injection is that you have to be some kind of tuning computer wizard/engineer* to be able to tweak an EFI engine to run properly on the street. Much of this reluctance comes from enthusiasts with little computer experience. The truth is that EFI tuning tables and systems have never been simpler. There are only two main maps that control an aftermarket EFI system-one for the fuel and one for spark. These maps are actually simple grids. In the case of a speed-density system, the base fuel map consists of a horizontal scale that specifies engine rpm. The vertical scale is usually expressed in kPa, which is the abbreviation for kilopascals. A pascal is the metric measurement for pressure, with 101 kPa equal to 1 atmosphere, or 14.7 psi. For a normally aspirated engine, the vertical scale would read from around 10, which is very low absolute pressure (equal to high vacuum), on the bottom to 100 kPa (WOT) at the top.