Avoiding
MOT Failure
Emissions - Petrol 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.
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.)
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Black
smoke usually indicates unburnt fuel. This usually occurs with
faults in the injection or carburettion system or a blocked or dirty
Air Filter.