What's An ECU?

The Engine Control Unit (ECU) controls the mixture of fuel and air within modern engines. The ratio or 'mix' determines the power as well as the efficiency of an engine. The configurable nature of ECU's has spawned the art of performance chip tuning whereby engine tuning can be manually modified to suit various driving applications.

The ECU utilises performance maps to provide the most optimal tune for regular engine performance. Modifying the performance map is what yields changes in efficiency and power.

For road applications the ECU engine tuning would normally favour a performance map that utilised less fuel and air. The effect is a saving in fuel consumption.

For competition purposes the chip tuning would favour an increase in fuel and air. However the ratio would be variable depending upon the ambient conditions as well as the effectiveness of the ignition spark.

The algorithm that determines the mix as well as the delivery of the spark is primarily what differentiates one Engine Control Unit from another.

Vehicle manufacturers prohibit access to the engine control unit as variations to the program could cause the engine to fail. During the servicing process the authority appointed by the manufacturer will routinely verify if the performance map has been modified. The consequences of a modification can either be that the service is refused or that the warranty is invalidated.

ECU's are not limited to road vehicles. Most modern modes of transport including motorcycles, prime movers (trucks, semi's), earth moving equipment, scooters, buses, trams and even golf carts utilise engine control units.

Typically they're a metallic box similar in size to an average paperback novel. They have the ability to not only control the performance map but more recently they've been designed to log the events. This provides various authorities the ability to recall and analyse these events thus making the ECU a type of black-box recorder.

In the racing world this is particularly useful as it allows engine tuners and drivers to analyse the performance of an engine during the course of a lap or stage.

As an example, if the analyses shows that fuel pressure at a particular point within the rev range (number of engine revolutions per minute) is in decline then the engineers would be able to deduce that the power would be adversely effected at that time. The theoretical solution via performance chip tuning would be to encourage the additional delivery of fuel during that phase of the lap or stage.

Next week we'll cover the control of ignition timing and idle speed within the ECU.