Easy EFI, Part 2

In the first installment (Easy EFI, Part 1)  we looked into the basics of factory stock electronic fuel injection (EFI) systems. These speed-density and mass-airflow systems work great on mild engines, offering numerous advantages over carburetion, but they are extremely limited when it comes to engine modifications. Any time the engine is altered, the factory electronic control module (ECM—ie., the computer) will require a recalibrated chip. This chip-burning process is time-consuming and expensive. If you have a modified engine and are continually tuning for more power, then you’re ready for the aftermarket world of EFI.

Once you have decided to explore the EFI aftermarket, your options are almost endless. Aftermarket EFI systems can be broken down into two separate areas. EFI hard parts include the intake manifold and throttle body. The other half is the electronic side, which includes the wiring harness, sensors, and ECM. All aftermarket EFI systems are stand-alone units. This means that the system is not tied directly to a specific vehicle or engine combination. With the correct sensors and wiring harness, most aftermarket ECMs are capable of managing the fuel and spark for any four-, six-, or eight-cylinder engine.

Improved mileage, throttle response, and lower emissions are all directly related to the EFI system’s ability to control both the fuel and spark. The ECM’s tuning options allow you to easily reconfigure the timing curve and air/fuel ratio at any engine speed or airflow.

This broad control comes at a price, however. A complete, ready-to-bolt-on EFI system typically goes for around $2,500, although some, like the Edelbrock Pro-Flo package cost as little as $1,800. Once you’ve acquired an EFI system, you’ll need a laptop computer (you can rent them cheap) and a willingness to learn. If you posses the ability to send and receive e-mail, then you are more than capable of tuning the ECM.

Within the ECM’s software system there are several screens that are used to control the different functions of the engine. These screens allow you to adjust things such as the engine’s basic fuel curve, timing, and various other control circuits along with the main spark map. Some screens appear as boxed matrixes such as the main fuel map. This is easily the most important map in the entire program. As the engine operates under various conditions, you can watch the cursor move around the map based on the engine load. During engine operation, several boxes within the map are highlighted showing where the ECM is reading its information. While editing the main fuel map, you can add or decrease the values of each number until you arrive at an optimum air/fuel ratio. This is the equivalent of changing jets or timing with the push of a button.

There are numerous screens within the ECM that are used to read other sensor information. Some screens are designed as maps, while others present data as charts and graphs. The screens may appear cluttered and confusing at first, but they’ll become less intimidating after you get used to how the system operates. An important part of the fuel injection system is the actual injector itself. The injectors can be looked at as variable-sized jets that are capable of flowing certain ranges of fuel. Injectors are sized by their ability to flow fuel. This is usually given in pounds per hour (lb/hr). A typical 30 lb/hr injector is capable of flowing sufficient fuel to support around 400 hp.

Terms such as duty cycle and pulse-width also relate to the injectors. Few machines can operate at 100 percent capacity for 100 percent of the time. Fuel injectors are no different. The duty-cycle of an injector refers to the percentage of time the injector has a large voltage value (5 volts or greater). An injector should operate at less than an 85-percent duty-cycle to keep from overheating. The pulse-width of an injector refers to the amount of time the injector is actually open and allowing fuel to be injected into the engine. This time is generally in milli-seconds of pulse width. Injectors are typically fired in either a batch or individually in a sequential order. Batch fire is when all the injectors fire simultaneously at one time for each revolution of the crankshaft. This means each injector offers a wider response of fuel-flowing capacity since it is fired twice for every four-stroke engine cycle. A sequential EFI system fires each injector only once based on the firing order of the engine.

This requires timing sensors for both the top dead center and camshaft position sensor. A sequential firing order also requires an injector with a larger capacity since it only fires once to deliver the correct amount of fuel. Once the firing order has been established, the injector flow rate must be taken into consideration. There are low-impedance and high-impedance injectors that are basically distinguished by their flow capabilities. A low-impedance injector is usually used in high-flowing applications that demand a high current draw. This high current draw requires one driver per injector in the computer. A driver is an electrical device within the ECM that controls the pulse width of the injector.

Low-impedance injectors are typically used in race-only engines requiring large amounts of fuel. The other type of injector is a high-impedance unit based on the factory design. One driver can typically run two high-impedance injectors since these offer a relatively low current draw. The stock high-impedance injectors are still capable of supporting engines with horsepower levels of up to 650 hp.

EFI systems operate at the relatively high fuel pressure of 40 psi. This requires a dedicated fuel system with high-pressure lines, pumps, filters, regulators, and a return line to keep the fuel system working properly. Refer to last month’s EFI story for a more detailed layout of this system.

One thing that is commonly overlooked on an EFI car is the current demand from all the electrical components. A properly configured charging system should be sufficient to support items such as lighting, cooling fans, A/C, heater fans, a stereo, a fuel pump, fuel injectors, and the ECM. With the simultaneous use of all these components, a factory alternator can easily become overwhelmed. A wise choice would be an alternator capable of putting out between 90 and 100 amps at idle.

While the fuel-injection world may seem complex, it is quite simple once you become familiar with the terms and components involved. EFI may not be for everyone, but those who choose to give it a chance will be rewarded with a more efficiently operating vehicle. EFI will open up worlds of tuning options and better performance if you are willing to take the plunge.