Engine Management &
Diagnostic Cheddar

Clutches, Gearboxes & Dual Mass Flywheels Cheddar

Engine Management and
Diagnostic Cheddar

The Engine Management system in your car is processed through the ECU/ECM (Engine Control Unit/Module) This is the brain of the car so to speak. Through this the process of reading the information sent to it via the sensors around the vehicle is calculated. Sensors are items like Lambda, Fuel pressure, Temperature, The information is interpreted from the data that the vehicle is programmed with and then sends out to actuators to adjust the engine accordingly.


These messages are areas like air-fuel mixture, ignition timing, idle speed, which the actuators control via mechanical & pneumatic and even electrical means. On-Board Diagnostics (OBD) is a motoring term that refers to a vehicle’s self-diagnostic and reporting capability. OBD systems give the vehicle owner or repair technician access to the status of various vehicle sub-systems. The amount of diagnostic information available via OBD has varied widely since it’s introduction in the early 1980’s. Early versions of OBD would simply illuminate a malfunction indicator light if a problem was detected but would not provide any information as to the nature of the problem. Modern OBD implementations use a standardized digital communications port to provide real-time data in addition to a standardized series of diagnostic trouble codes or DTC’s, which allow one to identify and remedy malfunctions within a motor vehicle.

Although most vehicle diagnostics are not as simple as just plug in and see what the fault code is and replace that part. Fault codes are an indication of what the ECU has recorded as information that is different or out of tolerance from its preset manufacturing data. So further diagnostics is needed, various tools help us to do this, some of the equipment we use are: Multi-meter, Oscilloscope, Gas analyser, Fuel pressure gauge, Vacuum gauge, as well as the experience of our technicians. At Auto-Mech we have diagnostic equipment to run checks on your vehicle.

For a number of years, EGR has been used to assist in the reduction of the emissions of NOx. NOx is often referred to as Oxides or Nitrogen and these gases are formed during the combustion process if the combustion temperatures become excessive. In general terms, the higher the temperatures during combustion, the higher the levels of NOx, a figure of around 1,800 degrees centigrade is often quoted as a temperature above which excessive levels of NOx are formed. NOx is in fact a generally used term to cover the Oxides of Nitrogen that commonly exist in the exhaust gases. Nitrogen monoxide (NO) is a particular combination of Nitrogen and Oxygen, and because both gases are present in the atmosphere they are induced into the engine. High combustion pressures and temperatures accelerate the formation of Nitrogen Monoxide, which, once it has left the exhaust port, combines with oxygen to form Nitrogen Dioxide (NO2). NOx is a colourless gas, which can cause paralysis if it enters the bloodstream. NO2 can cause respiratory irritation and can damage the lungs. Additionally, Oxides of Nitrogen combined with Hydrocarbons can form smog. The reduction of NOx emissions in general, is therefore, high on the priority list. Legislation in the UK, USA, EEC, Japan and other countries has for some time forced vehicle manufacturers to fit additional equipment to aid the NOx reduction. The basic problem with regard to the internal combustion engine and NOx is that high combustion temperatures cause an increase in the speed of NOx formation and higher levels of NOx are produced. Also NOx levels increase when mixture strength (air/fuel ratio) is slightly lean (excess Oxygen), and these levels occur around the cruise to light load range. Any aspect of the engines design or operation that is liable to increase combustion temperatures, especially when the air/fuel ratio is slightly lean, is going to result in high NOx emissions. As an example, many modern engines run fairly high compression ratios which cause high combustion temperatures, also the advanced ignition timing usually used when the engine is running on the leaner mixture also causes high combustion temperatures. These conditions will only serve to increase the NOx emissions. The EGR system allows a percentage of the exhaust gas to be fed back into the intake system. Exhaust gas is non combustible (it may contain an extremely small amount of hydrocarbons which has no effect on the process) therefore, if a small amount of exhaust gas is mixed with the fresh air/fuel mixture, it occupies a portion of the mixture that would otherwise be combustible and less heat will be produced. Additionally, the recirculated exhaust gas absorbs some of the heat produced during combustion. In total the combustion temperatures are reduced thus reducing the formation of NOx.

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4 & 5 Mendip Vale Trading Estate,
Wedmore Road
BS27 3EL