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EVAP System
testing using a
Smoke Machine
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Purpose
• A smoke machine is used
to identify leaks in
systems that hold and
transfer air and vapor.
Usage
• The primary function of the smoke machine is to test
the integrity of the Evaporative Control System
• The smoke machine can also be used to detect:
– Intake air system leaks
– Exhaust system leaks
– Cabin air/window seal leaks
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Other Test Applications
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Air cleaner assembly
Air ducts
Air valves
Component testing, prior to
assembly
Diaphragms
EGR valve
Exhaust manifolds cracks
Fuel tank pressure sensor
Intercoolers
Intake gaskets
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Injector o-rings
Loose clamps
Map sensors
Mass air flow meter
Oil leaks
PCV valve and hoses
Throttle body shaft
Turbochargers
Vacuum hoses
Vacuum switches
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Visible smoke pinpoints the leak
source
• A leak in the vapor recovery system can
be easily identified by the presence of
smoke at the gas cap
Smoke machine components
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Large tailpipe
plug
Smoke
oil
Smoke
dispersal
adapter
12 volt
power
cables
Vacuum pump adapter
Wireless
remote
Exhaust pipe
cone adapter
Plugs
Smoke outlet
hose
UV glasses
Schrader valve
removal tool
EVAP test port
adapter
UV light
source
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Smoke oil
• The smoke machine generates
smoke by passing mineral oil over a
red hot electric heating coil
• The oil contains a chemical that
glows bright yellow when exposed
to Ultra Violet [UV] light
Ultraviolet Light source
• An LED type UV flashlight
is used to pinpoint the source
of leaks
• Condensed smoke oil
will glow
green/yellow when
exposed to UV light
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Never look directly into the UV light
• Exposure to UV light can
cause permanent damage to
the retinas of your eyes
• Yellow UV safety glasses should be worn whenever
working with UV light sources
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Condensed smoke
oil
• Smoke vapor will
generally not glow
when exposed to UV
Light
• A small amount of smoke vapor will condense around
the places that the smoke leaks out of. This liquefied
smoke will glow
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Check the oil supply
• A dipstick is attached
to the smoke machine’s
oil filler cap
• Unscrew the dipstick
and observe the level of
oil using the UV light
to illuminate the
dipstick
Checking the oil
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Full Mark
• Smoke oil is a clear liquid so it is difficult to see the
level on the dipstick without the aid of UV light
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Adding oil
• If the oil level is low add a few ounces of oil – do not
overfill
Connect to the battery
• The smoke machine is powered by the vehicles battery
via the 12 volt power leads at the back of the machine
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Hanging the
smoke
machine
• When the smoke
machine will be
used near the
engine the
machine can be
hung from the
hood latch
Air Line coupler
• The correct type of coupler needs to be installed to
connect the smoke machine to the shop’s compressed
air hoses
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Shop air fitting
• Compressed air from the shop’s air compressor is used
to push the smoke through the system being tested
• The correct air coupler fitting needs to be attached to
the smoke machine
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Vapor hose
• The vapor hose is used
to inject smoke into the
system being tested
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Cone adapters
• Rubber cones allow the vapor line to connect and seal
to a variety of different size and shaped openings
• The large cone adapter here is used to connect the
vapor hose to the exhaust pipe
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Plugs
• Plugs may be needed to seal opening where
components have been removed or where a
small amount of leakage is expected
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Air Diffuser
• To find air leaks around windows and
doors an air diffuser is used to spread
out the smoke
• The vehicle’s HVAC fan is set to high
speed while smoke is blown over the
edges of the windows and doors
• Any disturbance in the smoke may
indicate an air leak
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Adapter for EVAP test port
• Most late model cars have an EVAP system test port
that uses an ACME thread [similar to the fitting on tank
of R134a refrigerant.
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EVAP
test port
• The EVAP test port is located on the
vapor line between the purge solenoid
and gas tank
• The cap is normally a light green color
• The port is normally located under the hood but is
occasionally found underneath the car
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Vacuum pump port
• The auxiliary output port can
be used to connect a hand
held vacuum pump to the
smoke machine
• Some EVAP systems use
electro mechanical vacuum
pump located inside the fuel
tank to monitor EVAP system
integrity
• A source of vacuum is needed to test the operation of
the sensors and pump
Vacuum Pump
• During the test a small amount vacuum is applied using a
hand held vacuum pump
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Screen Display
Function select buttons
• There are 3 membrane switches on the
right side of the panel
– The display select button changes the units
of measurement displayed by the 3 digit
LCD matrix
– The orifice select button changes the size
of the flow restriction inside the smoke
machine
– The start button starts a 5 minute leak
down test and toggles the machine
between full flow and pulsed flow
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Display Indicator lights
• When illuminated an
‘Orifice Leak Size’ of
.040”, .020” or .010” will
be indicated on the LED
display
• When the ‘Flow L/M’ is
illuminated the LED
displays the smoke flow
rate in liters per minute
• When ‘Pressure in H2O’ is
illuminated the LED
displays system pressure in
inches of water
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Display Indicator lights
• The ‘Vacuum in H2O will
only illuminate when the
smoke machine senses that
the system pressure is
lower than ambient
atmospheric pressure
• The ‘Polarity Protect’
indicator will illuminate if
the power lead connections
at the battery are reversed
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Display Indicator lights
• The ‘Pass’ or ‘Fail’ light
will illuminate after a 5
minute leaks test has
been completed
• The three orifice size indicator lights indicate the size the
internal restriction in the smoke machines output port
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Display Indicator lights
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• The ‘Off/Decay’ light
indicates that flow of smoke
from the machine is turned
off
• When the ‘On’ light is
illuminated there should be
a continuous flow of smoke
passing through the smoke
vapor hose
• The ‘Low Flow’ indicator light indicates that the machine is
operating in pulsed mode. A puff of smoke is sent through the smoke
vapor hose every few seconds.
Inches of Water
• Very low levels of pressure or
vacuum are measured in units of
inches of water
• The amount of vacuum applied to
the tip of a straw that will cause
the water in the straw to rise one
inch equals a vacuum level of 1
inch H2O
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Inches of water - pressure
Pressure
source
Open to
atmosphere
• Pressure can be measured in inches of
water using a manometer
• A ‘U’ shaped glass tube is partially
filled with water
• One end of the tube is open to
atmospheric pressure
• The other end is connected to the
pressure being measured
• The difference between the water
levels is measured in inches
Select the type of gas
• After the power leads are connected to
the battery you have 5 seconds to
select the type of gas being used in the
test.
• The default value is ‘AIR’ = shop air
• If you are using compressed nitrogen
gas press ‘Display Select’ until ‘n2’ is
displayed
• If you are using compressed carbon dioxide press
‘Display Select’ until ‘CO2’ is displayed
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Select the display type
• Pressing the ‘Display select button
cycles through the three types of data
displays:
– Orifice Size
– Flow rate
– Pressure / Vacuum
• If you are performing a pass/fail leak
test the display must be set to orifice
size to finish the test
• When the display is set to pressure the vacuum LED
will illuminate if the system pressure is below the
ambient atmospheric pressure
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Start button functions
• Pressing the ‘Start’ button will begin
sending a steady stream of smoke
through the smoke/vapor hose
• This begins a timed 5 minute test of
the EVAP system
• Pressing the ‘ Start’ button a second
time will set the smoke machine to
pulsed low flow mode
• While in ‘Low Flow’ mode the smoke machine will
make a clicking noise
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Turning off the machine
• The machine will automatically shut
down after the completion of the 5
minute test or after 8 minutes of
inactivity
• Holding the ‘Start’ button depressed
for a few seconds will force the
machine into shutdown mode
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Low battery voltage warning
Lo bAt
• A ‘Lo bAt’ warning message will be displayed if the
battery voltage level is below 11.0 volts
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Remote start/stop
• The smoke machine comes with a remote key fob that is
used to start and stop the flow of smoke
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Max Pressure and Flow Rate
• Maximum smoke pressure = 13.0 inches of H20
• Maximum flow rate = 10 liters per minute
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OBDII EVAP System
EVAP test port
Purge
Solenoid
Vent Solenoid
Charcoal
canister
Intake manifold
Sealed gas
cap
EVAP Pressure sensor
Roll over valve
Pressure
release
valve
Fill limit vent
valve
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Canister and vent solenoid
• The charcoal canister and vent solenoid are located
under the vehicle and within a few inches of the fuel
tank
Vent to
atmosphere
Charcoal
canister
Vent
solenoid
Purge line
Vapor line
to tank
Purge solenoid
Purge line
connects to
canister
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• The purge solenoid controls the rate at which gasoline
vapors are removed from the canister during the drive cycle
• It is normally found under the hood
EVAP Monitor
• All OBDII systems run a non-continuous monitor on
the evaporative emissions system at least once in every
trip
• There are two test performed in the EVAP system
monitor:
– A system integrity [leak] test
– A system performance test [flow test]
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EVAP Monitor
• If either test fails in two consecutive trips the Check
engine light will illuminate and a code will be set
• EVAP system codes range from P0440 through PO470
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EVAP System integrity test phase 1
Purge
Solenoid
- open
Vent
Solenoid
- closed
EVAP
Pressure
sensor
• During the first phase of the test the PCM commands the vent solenoid closed
and pulses the purge solenoid to create a partial vacuum within the tank
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EVAP System integrity test [leak test]
• After enabling criteria are met the PCM commands the
canister vent solenoid closed and sends a PWM current
[pulse width modulated] to the purge solenoid to allow
a small partial vacuum to build up inside the gas tank
• When the pressure inside the tank reaches a preset
amount – typically around 10 inches of water – the
purge valve is commanded closed
• Pressure inside the tank is monitored for the next few
minutes
EVAP System integrity test phase 2
Purge
Solenoid
- closed
Vent
Solenoid
- closed
EVAP
Pressure
sensor
• When the pressure sensor reaches a preset value the PCM closes the purge
solenoid. The vent solenoid remains closed. The PCM monitors the change in
pressure inside the tank for the next few minutes.
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EVAP monitor – system integrity test
• If there is a rapid rise in tank pressure after the purge
solenoid closes there must be a large leak – greater than
.040” . The EVAP integrity test fails.
• If the tank pressure slowly rises over a period of several
minutes the total leak size must be smaller than .020”.
The EVAP integrity test passes.
• The EVAP monitor then begins the system flow test.
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EVAP monitor – flow test
Purge
Solenoid
- cycling
Vent
Solenoid
- open
Upstream
oxygen
sensor
• The flow test looks at the changes in short term fuel trim as the duty cycle
applied to the purge solenoid is altered by the PCM.
EVAP monitor – flow test
• During the flow test the canister vent solenoid is open
and the duty cycle [PWM] applied to the purge
solenoid is slowly increased until it reaches 100% open.
• The PCM looks at 3 factors:
– Short term fuel trim [STFT]
– Idle rpm
– IAC or Electronic throttle control idle position
• If any of these factors change significantly as the duty
cycle on the purge solenoid is increased the EVAP
monitor passes
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Troubleshooting EVAP system leaks
• If the check engine light is illuminated and a scan tool
reveals a code for an EVAP system leak the smoke
machine is the best tool to locate the source of the leak.
• A scan tool may be required to actuate the canister vent
solenoid to the closed position.
• Leave the scan tool connected after verifying the code
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Remove Schrader valve
• Before connecting the smoke machine to the test post remove the
Schrader valve
• The Schrader valve has left hand threads – turn the tool clockwise to
loosen it
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Install the test port adapter
• Thread the end of the adapter
on to the test port
• Hand tight only --- Do not
over-tighten
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Connect the smoke hose
• The smoke hose is connect
by pushing the cone shaped
hose end into the adapter
hose
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Setup smoke machine
• Connect the smoke machine to shop air [or CO2, N2 if available]
• Connect the electrical leads to the battery – check that the
polarity indicator is not illuminated
Go to Scan tool
• In the scan tool menu find the test menu for functional
test
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Scan tool EVAP test menu
• Find the EVAP test that allows the scan tool to
open and close the canister vent solenoid
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Scan tool EVAP test menu
• Select vent solenoid (on/off)
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Scan tool EVAP test menu
• Use the Y/N buttons to toggle the vent solenoid on
and off
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Scan tool – tank pressure sensor
• The scan tool page here displays the tank pressure
in inches of mercury
• To convert inches of mercury
to inches of water multiply by
13.5
• The pressure measured here is
9.86 inches of water
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Select the orifice size
• Press the orifice size button until
the correct orifice size is
displayed:
– .020” for vehicle built after MY
2000
– .040 for built between MY 1995
and 1999
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Start 5 minute test
• Press the Start button to begin the 5
minute test
• You can change the display to pressure
H20 or flow L/M during the test but
the display must be returned to orifice
size to get the pass/fail indicators to
function at the end of the test
Check for evidence of smoke leakage
• During the test raise the vehicle to examine all of the components of
the EVAP system for evidence of leakage
• The vent solenoid shown here is frozen in the open position
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Check the gas cap seal
• Open the fuel filler door to check the condition of the
cap seal
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Pass / fail indicators
• If there are any leaks
detected the fail
indicator light should
illuminate at the end
of the test
• The off/decay light
should also be on to
indicate that the flow
of smoke has been
turned off
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Small leaks
• Leaks that are too small to release visible smoke may
be detected by shining the UV light along the hoses and
around the canister. Condensed smoke oil should glow
green/yellow around any small leaks
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Finding exhaust system leaks
• A spare battery or jump box can be used to power the
smoke machine
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Cone adapter for exhaust
• If the vehicle has dual exhaust with a crossover one
tailpipe may need to be plugged
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Muffler drain
• Many mufflers have a condensation drain hole near the bottom
• Smoke coming out of the drain shown here is normal
• Seal the drain hole with a piece of tape to prevent the smoke
from the drain masking any other exhaust leaks
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Exhaust flex joint
• Pay special attention to the flex joint in the exhaust
where the front pipe connects to the exhaust manifold.
• Shine the UV light onto the exhaust manifold to detect small
cracks
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Finding intake leaks
• Since the throttle plate never closes
completely you will need to plug the
intake upstream of the throttle plate.
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Connect smoke hose to manifold
• There are normally several manifold taps that you can
connect to
Canister purge
solenoid
Smoke
hose
Vacuum
supply line
• For this vehicle we disconnected the vacuum supply
line for the purge solenoid
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Find the leaks
• When smoke is introduced into the manifold even very
small air leaks will emit smoke
Distorted
throttle body
gasket
Other uses
• The smoke machine is not limited to on car testing.
• The seals and gaskets of a rebuilt engine can be smoke
tested prior to installation
• If you can figure out a way to seal off the open areas of
the system you can smoke test almost anything
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