Not sure if there is already a thread about this, but smoke testing a car for vacuum leaks is one of the best troubleshooting steps you can take for idle/drivability issues. The basic idea is to connect a pressurized and smoke filled air source to your intake system, and smoke will pour out of any leaking source (AKA vacuum leaks). The car doesn't need to be running, which makes it convenient. Commercial machines to do this are very expensive.
You will need:
-air compressor with pressure regulator
-empty and clean 1 gallon or 1 quart paint container with lid
-hose barb
-about 6 feet of vacuum hose
-air hose quick connect fitting
Make two holes in the paint container lid, and either solder, JB Weld, or otherwise attach the hose barb and the quick connect fitting into the lid. I actually used a hose barb and quick connect that both had male 3/8" threads, and then screwed female 3/8" barbs on the bottom side of the lid, so there was no chance of them coming lose. I even used rubber gaskets to get a good seal. Probably overkill.
Set your compressor to about 2-3 psi and connect it to the lid. Connect the 6' vacuum hose to the hose barb. Throw an old dirty rag in the gallon container and light it on fire. Let it burn ~30 seconds and then throw the lid on. The fire should go out immediately and smoke will begin pouring out of the 6' vacuum hose. It should smoke for at least 30 minutes as long as you don't shut the air source off.
Take your AFM/MAF off of your intake boot, and find something round that is the same size, insert it in the intake hose, and clamp it down. You want a perfect seal there. I used an old small coffee can I had laying around.
Connect the vacuum hose to the intake system. This can be done at any vacuum point really... I'm not sure off the top of my head what's easy to get to on an m20, but I use the charcoal canister hose on my m60. I just remove the canister hose from the throttle body and install my smoke tester hose.
It's important that if you hold the throttle body open while the machine is hooked up. Also, don't crank the pressure up too much, it only takes 2-3 psi.
Anywhere smoke pours out, find the source and fix it. Once fixed, retest, as there may be more leaks that didn't originally puff out smoke since it was all pouring out of the first leak.
This is mine:
Here are a bunch of others that I found pics of, may help with some ideas to use what you have laying around to make one:
You will need:
-air compressor with pressure regulator
-empty and clean 1 gallon or 1 quart paint container with lid
-hose barb
-about 6 feet of vacuum hose
-air hose quick connect fitting
Make two holes in the paint container lid, and either solder, JB Weld, or otherwise attach the hose barb and the quick connect fitting into the lid. I actually used a hose barb and quick connect that both had male 3/8" threads, and then screwed female 3/8" barbs on the bottom side of the lid, so there was no chance of them coming lose. I even used rubber gaskets to get a good seal. Probably overkill.
Set your compressor to about 2-3 psi and connect it to the lid. Connect the 6' vacuum hose to the hose barb. Throw an old dirty rag in the gallon container and light it on fire. Let it burn ~30 seconds and then throw the lid on. The fire should go out immediately and smoke will begin pouring out of the 6' vacuum hose. It should smoke for at least 30 minutes as long as you don't shut the air source off.
Take your AFM/MAF off of your intake boot, and find something round that is the same size, insert it in the intake hose, and clamp it down. You want a perfect seal there. I used an old small coffee can I had laying around.
Connect the vacuum hose to the intake system. This can be done at any vacuum point really... I'm not sure off the top of my head what's easy to get to on an m20, but I use the charcoal canister hose on my m60. I just remove the canister hose from the throttle body and install my smoke tester hose.
It's important that if you hold the throttle body open while the machine is hooked up. Also, don't crank the pressure up too much, it only takes 2-3 psi.
Anywhere smoke pours out, find the source and fix it. Once fixed, retest, as there may be more leaks that didn't originally puff out smoke since it was all pouring out of the first leak.
This is mine:
Here are a bunch of others that I found pics of, may help with some ideas to use what you have laying around to make one:
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