Engine Management Systems – the common terms used. (Copyright Torque Developments International)
Torque Developments International Technical Director – Sam Borgman explains the common jargon.
This is just a loose guide to deciphering some of the jargon we use in automotive engineering to describe different  aspects of engine management systems.
Engine Management System  (EMS)  –

Basic EMS Diagram.jpg
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Engine management system is an umbrella term for a system taking care of the jobs which were originally performed by many separate systems in years gone by, for example even the most  basic engine management system will do the job of the following now obsolete components;
• Carburettor (fuel delivery) • Points (ignition coil charging and firing) • Choke (fuel enrichment for cold engine operation) • Rad fan switch (on/off function of cooling fans)
The benefits of an engine management system over and above the historically traditional mechanical methods of control are far too numerous to list exhaustively but it is true that all centre on the subject of adaptability. The problem with mechanical systems is that once they have been set they are fixed in one mode of operation and honestly in some circumstances this rigid work routine works just fine, however in the ever changing and sometimes chaotic world of the internal combustion engine adaptability turns out to be absolutely key to achieving both greater efficiency and greater levels of average torque production. The term engine management system is an umbrella term and is very broad. It can be used to cover every component related to the control of the engine, which can include all of the following;
• ECU • Wiring loom • Sensors • Ignition Coils • Fuel injectors • Solenoids • Stepper motors • Power relays
Engine Control Unit (ECU) –

Typical OEM ecu.jpg
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This is the term that we give to the box of electronics at the centre of our engine management system, any modern ecu is a microprocessor based computer possessing a modest amount of memory which can be loaded with a firmware that can then be programmed to enable system control by an engineer.
The most basic forms of ecu’s units are nothing much more than a small series of low current on/off electrical circuits controlled by the microprocessor, these simple on/off circuits would be used to allow ignition coil electrical control and fuel injector electrical control. The information such as when to fire the spark and for how long to open a fuel injector would be driven by simple a look-up table, the X axis would be something to represent engine load like perhaps the throttle position sensor voltage (TPS) and the Y axis would typically be engine speed in revolutions per minute (RPM).
The power of microprocessors used by the engine control units has shot up over the last 20years and this rate of improvement shows absolutely no signs of slowing down. This has led to the latest engine control units being incredibly powerful tools for automotive engineers, and allows them to design systems with the ecu to monitor an engines crucial functions, and where necessary enable the ecu to make corrective adjustments to the systems programming on the fly at full speed. Regularly these control systems cycle at speeds in excess of 1000hz.
Piggy-back engine control unit –

Piggy-back ecu system.jpg
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This term seems to me to be an area of significant confusion in the automotive after-market and it really need not be because the definition is simple enough. A piggy back engine management system is an engine control unit which does not directly control the engine, instead it controls the signals that travel to and from another ecu in the system which IS directly controlling an engine. The aim of the piggy back system is to manipulate a pre-existing system so as to gain programmable control of the critical functions of the overall engine management system such as fuel delivery or ignition timing.
As standard engine management systems become more complex and deeper embedded in to a vehicles technical architecture they are harder to simply “replace” with a standalone fully programmable unit. But the demand for aftermarket modifications such as forced induction systems or radical re-designs of intake or exhaust systems means that engineers do require programmable control and often piggy-back ecu’s are a financially palatable compromise.
Stand alone engine control unit –
The term “stand alone ecu” refers to an ecu designed to form the central hub of an engine management system and control an engine directly, but it is different from the typical type of ecu supplied with production cars from the factory primarily because it will be to a point universal. Making a truly universal ecu to suit all budgets and all engine types is wholly unfeasible so aftermarket ecu manufacturers design and build very specific types of ecu’s which are carefully targeted towards specific areas of our marketplace. These units carry with them the features and technical capabilities that will hopefully be useful to the targeted end user. The three broad markets which are targeted by manufacturers of the engine management systems are;
High end motorsport and military

Bosch MS5.2 ecu.JPG
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• Formula racing. F1, GP2, Indy car. • Prototype racing. Lemans Series, ALMS • DTM, JGTC • Defence contractors. High altitude drones, armoured vehicles, robots • Moto-GP • Rally. WRC, Rally raid
Mid-budget motorsport

Motec M800 ecu.jpeg
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• GT racing. FIA GT1/GT2/GT3 • Lower formula racing. Formula2, Super league, Formula3, Formula BMW • Touring car racing. World touring car, British touring car, V8 supercars. • Power boat racing. • Superbike racing. • Prototype racing. VdeV, Radical, Sports 2000 • Drag racing. • Rally. Group A.
Clubman level motorsport

Haltech Sports 2000 ecu.jpg
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• Tin-top racing. One make series, Mazda, Fiat, Lotus • Lower formula racing. Formula Ford, Formula First, Formula Vee • Hill climb and sprinting. • Trackday cars. • Road use cars.
As an end user choosing the right ECU for your specific application can be quite difficult as good impartial advice can be very hard to come by. You’ll find that everyone you speak to will have a pet favourite system which is normally the only one they have proper experience with and all other systems seem “scary” to them. Some other people might have a financial interest in steering you one way or another and that should be accounted for because this part of your project is of critical importance and if you don’t pick the right system from the get-go you’ll be stuck with your decision going forward, so it’s important for the consumer to research the purchasing decision properly to avoid wasting their time and their money.
The way that I approach the problem is to look at the project and carry out an audit of all of the vehicles sub-systems both the pre-existing systems which will be retained and any sub-systems which are to be added during the course of the project, then crucially I take a good look at the overall budget and to cut a long story short find a unit that does everything we need it to do with some spare capacity on top and actually seek to spend as much as we can afford to on this aspect.
Programming manufacturers standard fit ECU’s (Chipping, Re-flashing, etc) –

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Having a modern car “chipped” is a phrase that most car enthusiasts will be familiar with but few people know what it means and even fewer know how it’s done, so I’ll try to shine a spot light on this slightly cloudy area. This is a process which involves forcing an OEM ecu to give up a copy of it’s hex decimal programming code, this copy of the code is then studied with the aim of discovering it’s structure by way of reverse engineering. Once the key control tables have been found in the hex code they can potentially be modified to effect a type of programmable control of the engine and it’s sub-systems. This newly modified programming code can then be uploaded back into the ecu’s memory. In an ideal world where the reverse engineering of the control code structure was 100% accurate the only major problem would be the long time delay between an engineer deciding they want to make a change and the effects of the change becoming available to measure.
As a real life example of what I mean lets look at the process of properly calibrating ignition advance, now with a fully programmable standalone ecu we might choose to set an engines ignition advance by holding the engine at a very specific amount of load and at a precise speed with a dynamometer and then in real time vary the amount of ignition advance whilst all the while monitoring the engines real time torque output plus other key measurements such as exhaust gas temperatures and exhaust gas composition, it would not be strange for a calibration engineer to test perhaps ten different ignition settings over a time of maybe ten seconds before settling on the optimum ignition timing for that load site and then moving onto the next cell in the ignition table and repeating the process. Conversely changing the ignition advance in an OEM ecu just once might take as long as thirty minutes, this makes calibrating the engine accurately an extremely time consuming task requiring days of dyno time.
More often than not, companies working with this kind of engine control technique do not spend days and days building accurate ecu control programs for their customers engines as ultimately it would prove unprofitable, instead the norm in this sector of the industry is to gather a program built by somebody else on a different car and attempt to copy and paste it into the customers car. As you might imagine this is not the most accurate and certain way to go about tuning an engine management calibration. In a nutshell, there is nothing wrong with the basic premise here at all, and if done properly this method can work very nicely, especially with complex modern road cars. The problem is that it is almost never done properly.
Written by Sam Borgman 2011

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