BMW Engine Management Systems

     The Motronic system (also called the digital motor electronics, or DME) is hands down the best overall fuel injection system when you consider price and performance. Ignition timing and fuel delivery are controlled by a digital map recorded in a removable chip within the main engine management (DME) computer. The computer takes input from a variety of sensors on the engine—cylinder head temperature, altitude (ambient air pressure), crank angle, throttle position, exhaust gas oxygen (mixture), ambient air temperature, and mass airflow—and adjusts engine functions accordingly. The DME chip is programmed by the factory with a map of certain performance parameters (mostly conservative, so the engine will react well under a host of varying conditions). Major changes to the engine (including different camshafts, exhaust, etc.) require an updated map to take full advantage of these modifications. Failure to update the Motronic system when significantly altering your engine may actually result in decreased performance, as the original system is finely tuned to supply the correct timing and fuel injection values for a stock engine configuration.

     Each factory Motronic system is matched directly to a specific engine configuration. Because of the proprietary nature of the Motronic system, there aren’t many changes you can perform without updating the DME chip. To gain the maximum benefit from engine modifications, either upgrade the DME chip or install a programmable aftermarket engine management system.

     Similar to the Motronic system, there are several complete aftermarket engine management systems that integrate fuel delivery and ignition system control. Electromotive and Motec manufacture two of the most popular systems for BMWs, although the market is expanding with many more choices as well. While these systems will squeeze the maximum performance out of your engine, they are not for the faint of heart, are technically challenging, and cost a pretty penny. They are without a doubt the most flexible of any fuel/ignition systems and will enable you to extract every ounce of power from your engine if you spend the time tweaking the system. Most are programmable from a laptop computer and can even interact with your computer both ways, giving you performance data and feedback from the engine as you run it through its paces. These systems cost anywhere from $3,000 to $10,000; however, they are usable on nearly any size BMW engine in any configuration.

     With the option of complete engine control, total power optimization becomes a reality. The latest engine management system from Electromotive is the TEC3r (Total Engine Control, Version 3), shown in Photo 1. This single-plug system costs about $2,500. It is far more advanced than previous versions and offers almost unlimited flexibility in designing your fuel and ignition systems.

     TheTEC3R system has a proportional air-to-fuel ratio table that allows you to systematically control the mixture from idle to full throttle. According to modern fuel injection theory, fuel and air combustion achieves its maximum efficiency at a ratio of 14.67:1. Although this ratio may be optimal for good fuel economy, it’s not best for maximizing power. On a normally aspirated engine at full throttle, maximum power is achieved with an air/fuel ratio set at about 13.8:1 to 14.0:1. On boosted engines, this maximum power ratio is closer to the range of 12.2:1 to 12.4:1. Using the variable fuel ratio characteristics of the TEC3r, you can create one set of programs for the track, where fuel delivery and optimum performance are critical, and another set for the street, where maximum fuel efficiency is desired. Because the TEC3r system senses engine load via a manifold absolute pressure sensor, the system can determine whether you’re cruising on the highway or driving on the track. One single program can also be designed for both applications.

     The system consists of a separate electronic control unit (ECU) and ignition coil packs. These coil packs, or direct-fire units (DFUs), deliver a full-charge spark up to 15,000 rpm. For a BMW inline six-cylinder engine, use a three-coil assembly. Each coil fires a spark for two cylinders that are opposite from each other in the firing order. By using a separate ignition coil for each pair of companion cylinders, the time available to recharge the coils increases by a factor of three (on the six-cylinder BMW engine). This configuration produces full spark energy while delivering spark duration up to 2 milliseconds at 6,000 rpm. This duration is more than 10 times longer than most capacitive discharge units and directly translates into better combustion and more power. For coil-on-plug engines, like the BMW E36 inline engine, stock ignition coils can be used in place of the DFU.

     Each coil pack is wired into two cylinders that are opposite of each other in the firing order (1 and 6, 5 and 2, 3 and 4). The ignition portion of the TEC3r system is wired so that the companion cylinders fire at the same time. Each coil fires a plug on the compression stroke for one cylinder and on the exhaust stroke for the companion cylinder. This produces what is known as a “waste spark” on the exhaust stroke of the companion cylinder. The cylinder that has compressed the air/fuel mixture receives a higher voltage spark than its companion cylinder, because the mixture creates an environment around the spark plug that offers a more conductive path. The majority of spark energy is delivered to the compressed cylinder. A small amount of spark voltage is directed to the cylinder on its exhaust stroke. This waste spark has no effect at all on the performance of the engine. Direct connection from the coil to each of the cylinders eliminates sending the spark through the distributor cap and rotor (on early cars), which can cause cross-firing and other distributor-related performance problems. In addition, computer-controlled custom advance/retard curves eliminate any mechanical problems that may occur with centrifugal or vacuum timing adjustment.

     The TEC3r ECU is dynamically programmed with easy-to-use software that comes with the system. The Tuning Wizard in WinTec 3.0 software allows you to create an instant engine profile in just a few steps (see Photo 2). By inputting all the parameters of your engine, you can start with a good base profile from which to make modifications. Mapped programs download to the ECU via a computer serial cable and can be updated, changed, or restored at any time. The base programs can be tweaked to get about 90 percent of the full power potential out of the engine. To achieve the final 10 percent, do extensive track testing or run your engine on a dyno.

     The TEC3r system works by sampling the values from sensors in the engine and comparing them to various tables that control fuel delivery and ignition timing. These sensors consist of the following:

Oxygen sensor: measures mixture by measuring the exhaust gases

Manifold absolute pressure sensor: measures pressure, while compensating for altitude changes; you can also substitute a mass airflow sensor instead of the MAP.

Knock sensor: detects and measures detonation caused by poor fuels or too much timing advance

Crank angle sensor: measures rpm and crank location

Throttle position sensor: measures position for idle control and how quickly the pedal is depressed for fuel enrichments (or deceleration cut-off)

Cam angle sensor: detects cam timing for true sequential mode fuel injection

Coolant sensor: measures engine temperature for warm-up enrichments

Manifold air temperature sensor: measures air temperature entering the engine for mixture compensation

Idle speed control: controls idle speed for warm up and air conditioner 

     These sensors work in conjunction to measure and create a picture of the engine conditions at any one point in time. The ECU takes the sensor readings and translates them into formulas for delivering fuel and firing sparks. Using advanced data-logging features, the sensor readings and the results of the ECU changes are recorded, snapping a picture of all the engine functions at any point. The data can be recalled for analysis and used as a reference for future programming of the ECU.

     The TEC3r operates in either phased sequential or true sequential mode. Phased sequential means the fuel injectors are activated multiple times per crankshaft cycle—once on an open valve and once on a closed valve. Early versions of the Motronic system were designed as phased injection systems. The fuel injectors on one-half of the engine would all open and close together. They share the same wiring harness and are electrically controlled as a group. True sequential injection means that each injector is activated in close coordination with that cylinder’s ignition cycle. Fuel squirts out of the injector in precise coordination with the opening and closing of the intake valve. Fuel is never injected into the cylinder head when the valve is closed. The TEC3r, operating in true sequential mode, injects fuel only when the intake valve is open, which smoothes out the engine idle and creates a cleaner-running engine. At higher rpm, phased sequential and true sequential modes show virtually identical performance, as the injectors are firing almost continuously.

     Another advantage to the TEC3r system is its flexibility; it can be used on just about any engine. Its ability to run engines up to 12 cylinders means it can be moved from one engine to another as you upgrade. It’s a very worthwile investment that can grow with you even if you upgrade your engine or your car.

     Pushing the limits of ultra-high performance, the TEC3r also has four general output parameters (GPO) that can be controlled by any number of engine conditions. For instance, the system can automatically turn on cooling fans or open electric thermostats if the engine temperature or rpm increases past a certain threshold, or provide the driver with a custom-designed shift light on the dashboard. In what could be the ultimate performance system, the TEC3r can control a variable turbo boost valve coupled with a knock sensor. This would allow you to run the maximum possible boost on a turbo or supercharged engine while actively monitoring and correcting for detonation. The engine management system can control this boost pressure, engine timing, and a host of other variables to achieve the highest possible boost without inflicting collateral damage. This system would be able to dynamically compensate for any octane fuel—automatically adjusting the timing and air/fuel ratio to squeeze the most power out of the engine.

     The TEC3r system can run in an open- or closed-loop configuration with respect to air/fuel mixture measurement. Open-loop mode is useful for racers who run leaded race fuels that cannot be used in conjunction with an oxygen sensor. In this mode, the system reads measurements from its sensors, and then compares the readings to its internal program maps. Spark and fuel mixture are controlled using these maps, without correcting for changes that would normally be measured by the oxygen sensor.

     The TEC3r is also able to self-diagnose problems with the engine’s sensors. The ECU has a check engine warning lamp that indicates if any of the engine’s sensors are producing faulty signals. The error codes isolate the exact problem and can be quickly downloaded from the ECU to diagnose the problem.

     The TEC3r is not specifically designed for the BMW and thus requires some adaptation to fit BMW engines. Sias Tuning manufactures a plug-and-play adapter kit that allows you to slide in the TEC3r unit in place of a Motronic DME, and replace the mass airflow (MAF) sensor with a manifold air pressure (MAP) sensor. The Sias Tuning kit is a good starting point for entry into the world of engine management. However, the plug-and-play adapter is somewhat limited in scope, because it uses all of the GPOs (general-purpose outputs) to control the various components of the car. The big advantage to an adapter like this is that you can simply reinstall the stock DME unit if you need to have the car checked for emissions. I recommend starting with an adapter kit. Then, if you seriously modify the engine, you can upgrade the engine’s sensors and create a specific wiring harness for the system.

 Why invest in one of these systems if you haven’t significantly modified your engine? Because they are really neat to play with, and you can custom design your own fuel and ignition maps. You probably won’t squeeze out any more horsepower than you would with a good aftermarket performance chip, but you will have fun playing around with the unit. On the other hand, if you want to design the ultimate engine, you need to install some type of engine management system. With a system like this, you can design and build any engine combination you want. Whether you desire a supercharged, boosted engine, or a super-high-compression-ratio engine that runs on pump gas, the engine management system will be able to control and optimize it. The possibilities are truly endless and unbounded.