In custom tuning I tend to see many cars today with mods that cause some type of leak, if its the exhaust design or air intake path.

This highly effects how the engine management adjusts the calibration incorrectly.

In searching for a automotive tool that injects smoke to track down leaks I found they cost around $1,200 plus so I designed one that would cost less then about $50 or even less if the parts are lying around.

Vacuum Leak Testing
• Select an appropriate vacuum line to access the vacuum system. The brake booster supply line before the check valve is a good choice.
• Seal system openings such as the air intake. If the brake booster line or any other line leading to the intake manifold is selected for the test connection, the air intake must be sealed to prevent smoke from leaking back through the intake. If the vehicle has a round inlet tube from the air filter, the Exhaust Cone adaptor will seal this opening without disturbing other connections and may serve as the access point for smoke. Otherwise, to seal the intake, use the supplied Cap Plugs, a latex glove or cellophane wrap with a rubber band. If none of these methods are possible, pack the venturis with cellophane using a soft stick or the end of a pencil. Seal the exhaust pipe using the supplied Exhaust Cone, a latex glove or rag.
Note: To use the Exhaust Cone as a plug, you must seal the 3/8” diameter inlet on the Exhaust Cone with the yellow cap plug provided.
• Set up the machine for operation per above.
• This procedure will not only locate leaks in vacuum lines but in many other components such as; EGR valves, oil seals and gaskets, idle motors and solenoids, inter-coolers and turbochargers, injector o-rings, ducting, throttle shafts, base gaskets, diaphragms, canisters and fittings to name a few.

Important!! It is always best to test in a draft free area. Always use a bright halogen lamp to enhance the visibility of the smoke exiting the leak.
Exhaust Leak Testing
• Insert the Exhaust Cone Adaptor into the end of the tailpipe. If the automobile has dual exhaust with a cross over pipe, simply plug the other pipe with a rag, tape, or latex glove with a rubber band.
• Set-up the machine for operation per Item 1 above.
• This test is most effective when the exhaust system is cold. Small leaks are sometimes sealed as the exhaust system heats up due to thermal expansion. A hot catalytic converter may consume some of the smoke in front of the converter. Remember, all testing is performed with the engine off!
Under Dash Leaks
• Most vehicles have a common vacuum line leading from the dashboard, through the firewall, to a vacuum source under the hood. This line supplies vacuum to climate control functions and other vacuum operated systems. Locate this line under the hood and disconnect it at its source. We will use this line to check under the dashboard for leaks.
• Set up the machine for operation per Item 1 above.
• While pressure or smoke is being fed into the vacuum supply line, observe the Flowmeter or Output Pressure Gauge. Change the climate control selector lever or button from heat to vent, to defrost, etc. As the lever is moved, a change in the flowmeter or pressure gauge reading will determine which system is leaking. Set the lever in the position that registered a reading while looking for the leak under the dashboard using a bright halogen lamp. This method will thoroughly inspect this system for leakage.
• Inspection of the central locking system is performed in the same manner. Access the control solenoids and activate them while introducing smoke into the system.
Fuel Vapor Recovery System (EVAP)
• According to the Environmental Protection Agency, the EVAP system is the most neglected of all the emission systems in an automobile. A leak as small as 0.020” diameter can allow over 30 times the allowable hydrocarbons into the atmosphere then is currently acceptable through the exhaust. Additionally, EVAP system leaks can be a major cause of check engine lights occurring. In the past, EVAP related problems have been difficult to locate and repair. These can now be quickly diagnosed and repaired, becoming a profitable ticket for service facilities.
• There are several acceptable methods of inspecting the EVAP system. Basically we need to close any vent solenoids, fill the system with smoke, and look for the smoke escaping at the leak. Since these systems vary in different vehicles and have evolved over the years, we will attempt to describe operating guidelines that should be helpful in inspecting these EVAP systems.
• Beginning with the 1996 model year, U.S. Vehicles have been produced with an EVAP Service Port to access this system. The port is usually located under the hood, but may be located else were on the vehicle. To access this port for testing, remove the cap, then remove the Schrader Valve from inside the Service Port, using the supplied Schrader Valve Removal Tool.

Important Note: The Schrader Valve has left-hand threads, turn clockwise to remove! Connect the supplied Service Port Adaptor to the Service Port.
• The Onboard Diagnostics on vehicles 1996 and beyond will determine if a leak exists, the following trouble codes may appear to report the leak:
PO442 for a .040 leak standard
PO456 for a .020 leak standard.
• Using a scan tool, close the vent solenoids so that the EVAP system is closed to the atmosphere.
• Set up the machine for operation per Item 1 above.
• Remove the fuel cap and begin to fill the system through the Service Port Adaptor until dense smoke is seen exiting the fuel neck. This procedure ensures that the system is full of smoke. Replace the fuel cap and continue pumping smoke into the system.
• Inspect under the hood for leaks using a bright halogen lamp. Raise the vehicle on a hoist and inspect the underside of the vehicle, tracing the route of the EVAP system.

Note: It may be necessary to hang the Smoker under the car so that it is visible to the operator.
• As the system fills with smoke, and the pressure in the system equalizes, keep an eye on the Flowmeter and the Pressure Gauge. If there is no leakage in the system the Pressure Gauge will go to its maximum pressure and the Flowmeter will drop to zero.
For trouble code PO456, the meter should stabilize at 0.05 LPM or less with the Smoke Pro™ connected to 100PSI.
For trouble code PO442, the meter should stabilize at 0.5 LPM or less with the Smoke Pro™ connected to 100PSI.
Note: These readings are approximate and are for reference only.
• Once the leak has been located and repaired, it is a good idea to repeat the above procedure using air only. It is not necessary to turn on the smoke to test for leakage using the Flowmeter.
• Replace Schrader Valve and cover. (Note: Valve is Left-hand thread.)

Maintenance

Oil Level:
Check the oil level regularly, approximately every 50 tests or so. The oil level should be maintained. When filling a new machine, add 8 oz of mineral oil or ATF. An alternate method for determining fluid level is to drain the oil from the machine and refill with 6 oz of mineral oil.

Trouble Shooting

No air flow

• Check that air is connected to machine
• Check that Flow Control Valve is open
• Check that the Smoke Supply hose is not kinked or pushed into machine

Poor smoke density or volume

• Check that oil level is correct
• Check that Flow Control Valve is open
• Check that battery is fully charged
• Check that the Smoke Supply hose is not restricted

High test pressure reading during a smoke producing cycle

• Check that the Smoke Supply hose is not kinked or pushed into machine
• Check that the Smoke Supply hose is not deadheaded

Oil Condensed in Smoker Supply Hose:
Due to the high density smoke produced by the Smoker oil may condense in the Smoke Supply Hose. This is normal. Should this occur, elevate the Smoker and let the full length of the hose hang down into a container to catch the small amount of oil in the hose as it drains. For best results, leave the Smoker in this position overnight.

Design could use a fan to move the smoke or best an air compressor which allows controlling flow via PSI.

Smoke tester I used back in 2005 I made as explained above

Still have and used it but now in 2022 Amazon asked if I would test and report my findings on this standalone smoke testing tool

This one is an Autool SPT 202, cost $180
It is fairly small as shown below
It has its own air compressor that will inject 10-15 PSI of generated smoke

It comes with hoses, nozzle and different size hose plugs
One useful adapter is an airbag which allows you to put in like a muffler tip or replace the MAF with this into the intake
Pump this up so that it makes an airtight path and in the center of this bag is a tube that carries the smoke through the airbag and directly
injecting smoke

Vendor states best to use baby oil, and only about 2 mL in smoker per use.
I suggest you use a mask or your mouth will smell of this oil

I tested this with a sealed bottle I made and made sure it had no leaks with smoker turned on for a good 15 minutes, and it has a pressure gauge
built in, and I found no leaks and pressure maintained at 13 PSI
I then added a small hole into the container and as shown below even in sunlight I could see and smell the smoke

Their user's manual is poorly written but being so easy to use you will get by doing proper smoke testing

This functions with a 12 D/C volts, most likely the vehicle's own battery or another voltage source

This can be used to locate leaks (even small ones) if used for vehicles like EVAP, intake, exhaust, A/C or hoses, etc
Also, could be used if looking for a leak like in plumbing pipes, etc.