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post #18 of (permalink) Old 16th November 2007
Technical Supremo

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The MAF on a diesel works quite different than those on a petrol engine. All diesels are known as open air breathers - there is no restriction in the air inlet - the only change is when the turbo (if fitted) kicks in as inlet air pressure will increase and is sensed via the turbo pressure regulator. On most equipment where there is no available signal the default temperature is 20 degrees C. The difficulty can arise when the engine is asked to start or run in very cold conditions and the ECU won't know when to add or reduce fuel. The ECU also takes many other factors into consideration - such as throttle voltage from the potentiometer, ignition timing, engine load and Lambda sensors. The air-flow sensor measures air speed and from this the ECU calculates the volume of air going into the engine per revolution and therefore is more likely to get the ignition mkixture not only correct but at its most economical setting. It must also be remembered that modern engines must comply with EU emmission standards - so by disconnecting the MAF it may fail on emmissions
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