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What is Engin Managment systems

 

Also known as EPU.

An engine control unit (ECU), is a type of electronic control unit the vehicle’s computer in other words, that controls a series of actuators on an internal combustion engine to ensure the optimum running. It does this by reading values from a multitude of sensors within the engine bay, interpreting the data using multidimensional performance maps, and adjusting the engine actuators accordingly.

Suppliers and installers of Power Mods, Dicktator, Rotortech MicroTech (for rotarys)

 

Working of ECU

Control of Air/Fuel ratio

For an engine with fuel injection, an engine control unit (ECU) will determine the amount of fuel to inject based on a number of parameters. If the throttle position sensor is showing the throttle pedal is pressed further down, the mass flow sensor will measure the amount of additional air being sucked into the engine and the ECU will inject fixed amount of fuel into the engine.

Control of ignition timing

A spark ignition engine requires a spark to initiate combustion in the combustion chamber. An ECU can adjust the exact timing of the spark (called ignition timing) to provide better power and economy.

Control of idle speed

Most engine systems have idle speed control built into the ECU. The engine RPM is monitored by the crankshaft position sensor which plays a primary role in the engine timing functions for fuel injection, spark events, and valve timing. Idle speed is controlled by a programmable throttle stop or an idle air bypass control stepper motor.

A full authority throttle control system may be used to control idle speed, provide cruise control functions and top speed limitation.

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 optimize the flow of air into the cylinder, increasing power and economy.

 

Programmable ECUs

A special category of ECUs are those which are programmable. These units do not have a fixed behavior and can be reprogrammed by the user. We at Racing boys use mainly the MicroTech system for all Rotary’s and Dictator for the majority of all other engines.

Programmable ECUs are required where significant aftermarket modifications have been made to a vehicle's engine. Examples include adding or changing of a turbocharger, adding or changing of an inter cooler, changing of the exhaust system or a conversion to run on alternative fuel. As a consequence of these changes, the old ECU may not provide appropriate control for the new configuration. In these situations, a programmable ECU can be wired in. These can be programmed/mapped with a laptop connected using a serial or USB cable, while the engine is running.

The programmable ECU may control the amount of fuel to be injected into each cylinder. This varies depending on the engine's RPM and the position of the accelerator pedal (or the manifold air pressure).

By modifying these values while monitoring the exhausts using a wide band lambda probe to see if the engine runs rich or lean, the tuner can find the optimal amount of fuel to inject to the engine at every different combination of RPM and throttle position. This process is often carried out at a dynamometer, giving the tuner a controlled environment to work in. An engine dynamometer gives a more precise calibration for racing applications. Tuners often utilize a chassis dynamometer for street and other high performance applications.

Other parameters that are often changed are:

  • Ignition Timing: Defines at what point in the engine cycle the spark plug should fire for each cylinder. Rev. Limit: Defines the maximum RPM that the engine is allowed to reach.
  • Water temperature correction: Allows for additional fuel to be added when the engine is cold, such as in a winter cold-start scenario or when the engine is dangerously hot, to allow for additional cylinder cooling.
  • Transient fueling: Tells the ECU to add a specific amount of fuel when throttle is applied. The is referred to as "acceleration enrichment".
  • Low fuel pressure modifier: Tells the ECU to increase the injector fire time to compensate for an increase or loss of fuel pressure.
  • Closed loop lambda: Lets the ECU monitor a permanently installed lambda probe and modify the fueling to achieve the targeted air/fuel ratio desired. This is often the chronometric (ideal) air fuel ratio, which on traditional petrol (gasoline) powered vehicles this air: fuel ratio is 14.7:1. This can also be a much richer ratio for when the engine is under high load, or possibly a leaner ratio for when the engine is operating under low load cruise conditions for maximum fuel efficiency.


Some of the more advanced standalone/race ECUs include functionality such as launch control, operating as a rev limiter while the car is at the starting line to keep the engine revs in a 'sweet spot', waiting for the clutch to be released to launch the car as quickly and efficiently as possible. Other examples of advanced functions are:

  • Waste gate control: Controls the behavior of a turbocharger's waste gate, controlling boost. This can be mapped to command a specific duty cycle on the valve, or can use a PID based closed-loop control algorithm.
  • Staged injection: Allows for an additional injector per cylinder, used to get a finer fuel injection control and atomization over a wide RPM range. An example being the use of small injectors for smooth idle and low load conditions, and a second, larger set of injectors that are 'staged in' at higher loads, such as when the turbo boost climbs above a set point.
  • Variable cam timing: Allows for control variable intake and exhaust cams, mapping the exact advance/retard curve positioning the camshafts for maximum benefit at all load/rpm positions in the map. This functionality is often used to optimize power output at high load/rpms, and to maximize fuel efficiency and emissions as lower loads/rpms.
  • Gear control: Tells the ECU to cut ignition during (sequential gearbox) upshifts or blip the throttle during downshifts.
    A race ECU is often equipped with a data logger recording all sensors for later analysis using special software in a PC. This can be useful to track down engine stalls, misfires or other undesired behaviours during a race by downloading the log data and looking for anomalies after the event.