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Avoiding
MOT Failure
Emissions - Diesel Engines
Make sure that
the engine is in good working order and tuned. Ignition timing, clean air filter
etc.
Start the engine and hold the revs at around 2500 rpm for about 20 seconds.
Allow the engine to return to idle and watch for any smoke from the exhaust pipe.
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If dark smoke comes
from the exhaust then the car will fail and need engine repair or further tuning.
Blue smoke usually means oil is being burnt. This usually occurs when worn
seals allow oil into the cylinders. (Valve stem oil seals or piston rings.)
Black smoke usually indicates unburnt fuel. This usually occurs with faults
in the injection or carburettion system or a blocked or dirty Air Filter.
Check that the idle speed is not too high (Usually between 600 - 1000 rpm)
For any further tests you will need the use of a gas analyser capable of measuring
Carbon Monoxide and Hydrocarbons. These can be hired or you could take your car
to a garage for a check.
Levels permitted for each car vary by model but the amount of hydrocarbons and
level of Carbon Monoxide produced from your exhaust must not exceed the levels
set by the manufacturers for model and age of car.
Further Help
Check Emissions
Emission Levels MOT
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