This
inspection applies to:
All compression
ignition engine vehicles with four or more wheels except quadricycles and electric/combustion
engine (Hybrid) vehicles
Reasons for not carrying out a smoke test
Do not carry out a metered smoke test if the engine is not in a safe condition
to do so. This will involve questioning the vehicle presenter and a brief examination
of the vehicle condition. The reason for not conducting a smoke test must be clearly
shown on the VT30. (See Introduction 2h).
When to do the test
The smoke test must only be completed when the engine is at normal operating
temperature.
It is not normally sufficient to run the engine with the vehicle stationary to
warm it up to temperature
The engine oil temperature measured by a probe in the oil level dipstick tube
is to be at least 80°C, or normal operating temperature if lower (60°C minimum).
Testing an engine below normal operating temperature may affect the test result
If owing to vehicle configuration temperature measurement is impractical, the
establishment of the engine’s normal operating temperature may be made by some
other means, for example by the operation of the cooling fan or the engine block
temperature measured by the level of infra-red radiation to be at least an equivalent
temperature
Smoke meter probe
With some types of smoke meter, care must be taken to ensure that the smoke
meter probe is correctly aligned with the exhaust gas flow. Reference to meter
manufactures instructions may be necessary
Suitable smoke meters
Suitable smoke meters are those accepted by VOSA, calibrated and maintained
in accordance with VOSA’s instructions
Suitable engine temperature measuring devices Suitable engine temperature measuring
devices are only those accepted by VOSA
Automatic transmission
When testing vehicles fitted with automatic transmission care must be taken
to avoid overheating the transmission system. Do not carry out unnecessary engine
acceleration or prolonged high revving of the engine. Reference to the vehicle
manufacturers instructions may be necessary
Recording emissions test results Record the results of the tests via the
VTS Device. (See Introduction paragraph 3 at the beginning of this Inspection
Manual).
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A. Vehicles
first used before 1 August 1979
Where possible check that:
• there is sufficient oil in the engine
• the oil pressure is not too low
• there is no abnormal engine noise
• the governor has not been tampered with
• the engine is at normal operating temperature (see information column)
raise the engine speed to around 2500 rpm, or half the maximum engine speed if
this is lower
hold this speed steady for 30 seconds to ensure that the inlet and exhaust system
is fully purged
allow the engine to return to idle and the emissions to stabilise
1. Assess the smoke emitted from the tailpipe
2. Rapidly increase the engine speed to around 2500rpm or half the maximum engine
speed if this is lower and assess the smoke emitted from the tailpipe during acceleration
B. Vehicles first used on or after 1 August 1979
Where possible check that:
• there is sufficient oil in the engine
• the oil pressure is not too low
• the camshaft belt is in a satisfactory condition
• there is no abnormal engine noise
• the governor has not been tampered with
• the engine is at normal operating temperature (see information column,
Page 1)
If appropriate, remove oil temperature probe. Raise the engine speed to around
2500rpm, or half the maximum engine speed if this is lower, and hold for 30 seconds
to fully purge the inlet and exhaust system
Raise engine speed slowly to maximum to check the operation of the governor.
Once the engine
speed has stabilised or if it becomes clear that the governor is not working,
release the pedal, return to idle and stop the engine Prompt the meter to carry
out a zero check
Check that the smoke meter probe can be inserted into the tailpipe
1. Insert the probe fully and securely, in line with the gas flow. Restart the
engine
Fast Pass
Following the meter prompts, depress the accelerator pedal quickly and continuously
but not violently, to reach full fuel position in less than 1 second
Hold it there until a release prompt is given, then immediately release the pedal.
Allow the engine, and any turbocharger fitted, to return to idle speed
At the end of the 1st acceleration read the smoke level displayed on the meter.
If it is at or below 1.50m-1 the vehicle has passed this part of the test and
a pass result will be displayed on the meter. Go to Method of Inspection 3
2. If the1st acceleration smoke level is greater than 1.50m-1 carry out two further
accelerations following the meter prompts
At the end of the 3rd acceleration, read the mean smoke level displayed on the
meter. If it is at or below the appropriate limit, the vehicle has passed this
part of the test. Go to Method of Inspection 3
If the mean smoke level is too high, carry out further accelerations up to a maximum
of 6 in total
After each acceleration, check the mean reading. This part of the test is complete
when either:
• the mean of any 3 consecutive smoke readings is at or below the appropriate
limit, or
• six accelerations have been performed
3. Assess whether the smoke emitted from the exhaust, regardless of measure density,
is likely to obscure the vision of other road users
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A. Vehicles
first used before 1 August 1979
1. The exhaust emits dense blue or clearly visible black smoke for a period of
5 seconds at idle
2. The exhaust emits dense blue or clearly visible black smoke during acceleration
which would obscure the view of other road users
Note: The criterion is density and not volume of smoke. The description ‘dense
smoke’ includes smoke or vapour which largely obscures vision
Older vehicles, particularly pre- 1960, sometimes emit unavoidable smoke due to
their design. Such smoke is not a Reason for Rejection
B. Vehicles first used on or after 1 August 1979
1. The emissions cannot be measured because a tailpipe accessory is fitted or
a deliberate modification has been made which prevents insertion of the smoke
meter probe.
Note: there is no Reason for Rejection for vehicles that do not meet the fast
pass criteria
2. After 6 free accelerations, the mean of the last 3 smoke levels is:
a. for a non-turbocharged engine, more than 2.50m-1
b. for turbocharged engines more than 3.00m-1
3. Exhaust emits excessive smoke or vapour of any colour to an extent likely to
obscure the vision of other road users
Note: The criterion is density and not volume of smoke. The description ‘dense
smoke’ includes smoke or vapour which largely obscures vision
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