Audi A6 engine acceleration abnormal sound reasons for failure analysis

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Failure phenomenon A 2004 Audi C5A6 sedan, equipped with 1.8T engine and automatic transmission, mileage of 100,000 km. The owner Reflects of the engine block has accelerated in the 2,3 "Tara Tara" different sound, the sound has been going on for about half the time, and from time to time, until the last two days the sound becomes apparent. After test found the sound really like the car owners said, heard "Tara Tara" sound when accelerating engine block outgoing 2,3, really like listening to the sound of the engine knocking sound, but the engine power has not been any impact, original accelerate the engine sound normal. I combine failure analysis, 2,3 gear acceleration when the engine can issue a "Tara" sound, principally for several reasons. (1) Variable valve timing mechanism failure. Because 2,3 gear acceleration when the engine has entered a medium- load conditions, according to the characteristics of the engine, the valve timing should have been entered in the regulation of position adjustment method is by changing the position of the chain tensioner to achieve. According to the principle known when the chain camshaft adjustment, if the chain tensioner power shortage will cause a chain in a relaxed state in the adjustment process and beep. (2) Since the engine knock sound is generated. That there are several possibilities: 1 fuel octane is too low cause detonation . This car's engine should be used more than 93 unleaded gasoline, it is best to use more than 95 unleaded petrol, otherwise it will knock. 2 premature detonation ignition timing. All these car fault diagnosed by appareil diagnostic auto.