An engine control unit (ECU), also commonly called an engine control module (ECM), is the brain of your car. It is the main reason that we are now in the second era of muscle cars, despite restricting emission regulations.
The ECU controls a series of actuators on an internal combustion engine to ensure optimal engine performance. It does this by reading values from a multitude of sensors within the engine bay, interpreting the data using multidimensional performance maps (called look-up tables), and adjusting the engine actuators. Before ECUs, air-fuel mixture, ignition timing, and idle speed were mechanically set and dynamically controlled by mechanical and pneumatic means.
In the early 1970s, the Japanese electronics industry began producing integrated circuits and micro-controllers for engine control in its automobiles. The Ford EEC (Electronic Engine Control) system, which utilized the Toshiba TLCS-12 micro-processor, went into mass production in 1975.
General Motors' (GM) first ECUs were a pilot program in 1979. They were a hybrid digital type that used analog techniques to measure and process input parameters from the engine. Then they used a look-up table stored in a digital ROM chip to yield pre-computed output values. Later systems computed these outputs dynamically. The ROM-type of system is amenable to tuning if you know the system well. The disadvantage of such systems is that the pre-computed values are only optimal for a new engine. As the engine wears, the system may be less able to compensate compared to other designs.
By 1980, all active programs were using microprocessor-based systems. Due to the large volume of ECUs that were produced to meet the Clean Air Act requirements for 1981, only one ECU model could be built for the 1981 model year. The high volume ECU that was installed in GM vehicles was a modern micro-processor-based system. GM also moved rapidly to replace carburation with fuel injection as the preferred method of fuel delivery for vehicles it manufactured.
Modern ECUs use a micro-processor which can process countless inputs from the engine sensors in real-time. An electronic control unit contains the hardware and software (firmware). The hardware consists of electronic components on a printed circuit board (PCB) and ceramic substrate or a thin laminate substrate. The main component on this circuit board is a micro-controller chip (MCU). The software is stored in the microcontroller, or other chips, on the PCB- typically in EPROMS or flash memory so the CPU can be re-programmed by uploading updated code or replacing chips. This is also referred to as an (electronic) Engine Management System (EMS).
Sophisticated engine management systems receive inputs from other sources, and control other parts of the engine. For instance, somevariable valve timing systems are electronically controlled, and turbocharger waste gates can also be managed. They also may communicate with transmission control units or directly interface electronically controlled automatic transmissions,traction control systems, etc. The Controller Area Network, or CAN bus automotive network, is often used to achieve communication between these devices.
Modern ECUs also include features such ascruise control, transmission control, anti-skid brake control and anti-theft control.
If the ECU has control over the fuel lines, then it is referred to as an electronic engine management system (EEMS). The fuel injection system has the major role to control the engine's fuel supply. The whole mechanism of the EEMS is controlled by a stack of sensors and actuators.
An ECU exerts controls over the following four major engine functions:
Control of Air–Fuel Ratio
Most modern engines use some type of fuel injection to deliver fuel to the cylinders. The ECU determines the amount of fuel to inject based on a number of sensor readings. Oxygen sensors tell the ECU whether the engine is running rich (too much fuel or too little oxygen) or running lean (too much oxygen or too little fuel), as compared to ideal conditions. The throttle position sensor tells the ECU how far the throttle plate is opened when the accelerator is pressed down. The mass air flow sensor measures the amount of air flowing into the engine through the throttle plate. Theengine coolant temperature sensor measures whether the engine is warmed up or cool. If the engine is still cool, additional fuel will be injected.
Control of Idle Speed
Most engine systems have idle speed control built into the ECU. The engine RPM is monitored by the crankshalf position sensor which plays a primary role in the engine timing functions for fuel injection, spark events and valve timing. A full authority throttle control system may be used to control idle speed, provide cruise control functions and top speed limitation. It also monitors the ECU section for reliability.
Control of Variable Valve Timing
Some engines have variable valve timing. In such an engine, the ECU controls the time in the engine cycle at which the valves open. The valves are usually opened sooner at higher speed than at lower speed. This can increase the flow of air into the cylinder, increasing power and fuel economy.
Electronic Valve Control
Experimental engines have been made and tested that have no camshalf, but have full electronic control of the intake and exhaust valve opening, valve closing and area of the valve opening. Such engines can be started and run without a starter motor for certain multi-cylinder engines equipped with precision timed electronic ignition and fuel injection. Such a static-start engine would provide the efficiency and pollution-reduction improvements of amild hybrid-electric drive, but without the expense and complexity of an oversized starter motor.
The first production engine of this type was invented (in 2002) and introduced (in 2009) by Italian automaker Fiat in the Alfa Romeo MiTo. The elimination of cams, lifters, rockers, and timing set reduces not only weight and bulk, but also friction. A significant portion of the power that an engine actually produces is used up just driving the valve train, compressing all those valve springs thousands of times a minute.
Once more fully developed, electronic valve operation will yield even more benefits. Cylinder deactivation, for instance, could be made much more fuel efficient if the intake valve could be opened on every downstroke and the exhaust valve opened on every upstroke of the deactivated cylinder or "dead hole." Another even more significant advancement will be the elimination of the conventional throttle. When a car is run at part throttle, this interruption in the airflow causes excess vacuum, which causes the engine to use up valuable energy acting as a vacuum pump. BMW attempted to get around this on their V-10 powered M5, which had individual throttle butterflies for each cylinder, placed just before the intake valves. With electronic valve operation, it will be possible to control engine speed by regulating valve lift. At part throttle, when less air and gas are needed, the valve lift would not be as great. Full throttle is achieved when the gas pedal is depressed, sending an electronic signal to the ECU, which in turn regulates the lift of each valve event, and opens it all the way up.
A special category of ECUs are those which are programmable; these units can be reprogrammed by the user.
When modifying an engine to include aftermarket or upgrade components, stock ECUs may or may not be able to provide the correct type of control for the application(s) in which the engine may be used. To accommodate for engine modifications, a programmable ECU can be used in place of the factory-shipped ECU. Typical modifications that may require an ECU upgrade can include turbocharging, supercharging, or both, a naturally aspirated engine; fuel injection or spark plug upgrades, exhaust system modifications or upgrades, transmission upgrades, and so on. Programming an ECU typically requires interfacing the unit with a desktop or laptop computer; this interfacing is required so the programming computer can send complete engine tunings to the engine control unit as well as monitor the conditions of the engine in real time. Connection typically used in this interface are either USB or serial. Two popular manufacturers of tuning software for Challengers are Diablo and HP Tuners.
By modifying these values while monitoring the exhausts using a wide band Lambda probe, engine tuning specialists can determine the optimal fuel flow specific to the engine speed's and throttle position. This process is often carried out at an engine performance facility. A dynamometer is typically found at these locations; these devices can provide engine tuning specialist useful information such as engine speed, power output, torque output, gear change events, and so on. Tuning specialists often utilize a chassis dynamometer for street and other high performance applications.
Engine tuning parameters may include fuel injection volume, throttle-fuel volume mapping, gear shift mapping, and so forth. While the mentioned parameters are common, some ECUs may provide other variables in which a tuning software could potentially modify.