 It used to be that tuning at the track was pretty much limited to jetting, timing and tire pressure. Those days have changed with the introduction of programmable engine management systems such as the Accel/DFI Gen 7, Big Stuff 3, and F.A.S.T. These and other engine management systems (EMS) have opened a whole new world of engine tuning capability for the racer that would have not been otherwise possible.
So what do these magic boxes really do? In simplest terms, engine management systems accumulate data about the engine’s operation and then send commands to alter fuel delivery events and spark timing based upon a predetermined set of calibration tables contained within. Aftermarket chips and piggyback systems do this through the vehicle’s existing ECU while stand alone EMS systems offer an entire new range of capabilities. Before we get accused of over simplification, let’s get into it with some more detail
Hardware Considerations
Engine management systems are typically categorized by the way they measure and operate. Determining engine load is a key measure for any EMS system. Drag race applications may use speed density systems which measure incoming air flow based on engine RPM and manifold pressure (up to 5 bar) to determine fuel and spark curve curves. These are typically found on boosted engine combinations. You’ll also see some systems that measure the angle of the throttle blade on a throttle body on naturally aspirated induction systems. Cars with factory calibrated OEM style EFI systems may use Mass Air Flow (MAF) systems which go one step further by using a TPS and MAP sensor with a mass air meter which directly measures the air entering the intake tract. Systems such as this are typically not used as they are restrictive to air flow and slower to react to varying engine loads.
EMS kits, which typically include an interface harness, sensors pak and wide band O2, can be broken down into either batch fire or sequential, which deals with how they pulse the injectors in the fuel delivery system. Batch fire systems are more typically used on an engine capable of producing less than 1,000 hp and fire all of the engine’s injectors at once. SEFI, on the other hand, is typically used on applications producing 1,000 hp or more and control the engine’s fuel injectors in conjunction with the engine’s valve events. Both systems can typically handle multiple sets of either low or high impedance injectors.
Besides this, buyers will also have to be sure that the part number they order is compatible with the vehicle’s ignition system. There are also a number of bells and whistles that can come either as standard or optional equipment. Wide band O2 capability, nitrous control, data acquisition and self diagnostics are just a few examples of some of the worthwhile options that might be of value.
Of course, no EMS system is able to do its job unless it has the data it needs to do its job. Data collection is handled by any number of strategically placed sensors that tell the ECU’s logic processor what it needs to know in order to react accordingly. Crank Angle or Cam Sync sensors help determine when the number one cylinder is at top dead center. Other temperature, pressure, flow, vibration and speed devices known as Coolant, Oil & Exhaust Gas (EGT) Temperature, Wide Open Throttle (WOT), Throttle Position (TPS), Manifold Pressure (MAP), Barometric Pressure (BP), Fuel Pressure, Velocity Air, Mass Air Flow, Knock and Vehicle Speed (VSS) sensors provide critical input as well.
While going into depth with regards to all of these components requires great detail and goes beyond the scope of this article, suppliers of specific EMS units should be able to provide what should be used for specific race and engine applications.
First Things First
For any engine control system to work to its full potential, you must first be certain that your engine is in good operating condition. Making sure you have a good battery with solid connections, enough coolant in the radiator and having clean, properly sized fuel injectors are typical of some of the things that should be checked.
Before installing the ECU and wiring harness, spend an evening or two to thoroughly familiarize yourself with the installation manual to make the process easier than we thought it would be. If your unit didn’t come with a printed one, it’s more than likely contained in the software that you’ll install into your laptop. Don’t try to go the typical route that many people do by playing with the software before you know what the consequences might be. This is not a computer game. You can destroy your vehicle’s engine.
To speed up the overall wire harness installation process, the interface harness that connects the ECU to the vehicle’s stock wiring harness usually comes with identification labels at the end of each wire or connector to ensure that each connection is terminated correctly. The best location for the firewall hole is typically close to the center of the vehicle so there’s plenty of length to connect to all the sensors on our engine.
Once all of the hardware is installed, the next step was to connect your laptop to the ECM and then look to see if all of the electronics can talk with each other. After you verify data is coming in from all of the sensors and check to see if the readouts were within expected ranges, you’re ready to start the engine.
Most systems come with a basic calibration that the owner can match to their own particular engine configuration so the engine could start and run. Users also have the option of entering their own data about the engine setup so the software can automatically construct a basic fuel and spark curve. Taking the time to establish that information correctly rather than guessing at it makes a big difference in getting to where you want to go with your tune up.
Understanding the Software
Assuming that any shop that bolts parts on a car can also tune a car electronically is a big mistake. It’s almost always easier to bolt the parts in place than it is to get them to work together at their maximum potential and, at the same time, not damage the engine. Basic computer skills are necessary along with a thorough understanding of tuning and the dynamics of modern engine controls.
In basic terms, the software package is really nothing more than an interface between the engine management system and the engine in your vehicle. It reacts to what strategically placed sensors on the engine and drivetrain tells it and then responds based on the parameters established with the tables or algorithms contained in the programmable software. There are also a number of optional sensors and actuators that are needed to optimize an engine’s power potential. To provide meaningful input from the richer air/fuel mixtures used for maximum power, a wide band O2 sensor is often used in order to better control the pulse width of the injector. Peak and hold injector drivers are needed to activate and control high flow, low impedance fuel injectors which are required in high horsepower applications. Data logging requires even more components.
Once the software has been successfully installed, communication with the ECU has been established and the hardware and operating parameters have been configured, users can then begin to manipulate the Air/Fuel Ratio, O2 Correction and Fuel tables. Fine tuning the engine for maximum power and drivability is a repeated process using these tables. That process involves configuring, in order, the air/fuel ratio table for different engine speed and load combinations, the positive and negative O2 correction tables and then the volumetric efficiency (VE) values in the Fuel Table.
Advanced tuners can even overcome inefficiencies in the intake manifold design by adjusting the amount of fuel (positive and negative) and spark advance/retard correction for each individual cylinder. Some EMS units can also be configured to even “learn” to a limited extent in order to minimize the amount of O2 correction required to achieve the user defined values in the air/fuel ratio table.
Making Changes
Many EMS systems come with a start up calibration to get your vehicle up and running so you can begin tuning your vehicle on a chassis dyno. These will be based on the number of cylinders, injector size, estimated horsepower and other parameters. Buying a system through an experienced tuner, however, might give you access to some calibrations they’ve already worked out on other vehicles that are already pretty close to what you want.
Once the engine warms up to 140-degrees, the O2 sensor should then begin displaying relevant values. If you’re not using a wide band O2 , remember the reading can be rather inaccurate as it strays away from stoichiometric. If your vehicle is not equiped with a mass air flow meter, you system will give you a Volumetric Efficiency (VE) table which shows the engine’s breathing efficiency under various rpm range and load conditions. Many tuners will start by setting identical A/F ratios at all the load points and then make small, methodical changes. By datalogging that information during a test drive, the playback function can be used to further refine and optimize settings. Spark advance can then be adjusted. Too much timing will cause detonation which will result in an underperforming engine. If you have individual Exhaust Gas Thermometers (EGT’s) on each exhaust tube, individual cylinder adjustments can then be used to address fuel distribution problems caused by air flow variations in the intake manifold and cylinder head design.
Just remember that EMS systems make decisions based solely on what the sensors transmit, it’s easy to understand how most problems are a direct result of inaccurate data or mechanical problems. For instance, incorrect fuel pressure or a clogged injector can result in a lean condition. A vacuum leak can make the EMS think the engine is running leaner than it actually is.
Programming a stand alone engine management system requires a thorough understanding not only of how a 4-cycle engine and its supporting systems work, but also of the software itself. The benefits are worth the investment, however as seen with the performance gains that result. |
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