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Boost leak testing: What it is and how to do it

6599 Views 10 Replies 7 Participants Last post by  sde780
New to the forums and noticed a lack of mention about the importance of boost leak testing. I've gained a lot of great info from this forum, so I thought I would give some back. Other turbo car forums I've been on have been covered with how to's and the reasoning behind it. If this has already been beaten to death, I apologize in advance.


Imagine trying to blow up a balloon. Now imagine the balloon has a few small holes in it. The balloon with holes will take more effort and a longer time to blow up. A boost leak is similar. Boost leaks will make your turbo work harder and take longer to get to your set pressure. It can also lower your max psi, depending on how you have your boost referenced. You WILL NOT usually be able to tell you have a leak by driving feel, so you HAVE to leak test. When you are doing a boost leak test, you are raising the pressure inside your system to about the max pressure you make during full boost. You do this so you can find the holes in your system and fix them.


You can either buy a boost leak tester from one of our wonderful sponsors OR


Quite easy. Go to your favorite local home depot / lowes. And get:

This guy. Now despite the fact that it says 2" elbow, it will fit 2.5" the compressor inlets which most of you should have. You could also get a straight section instead, but I prefer the elbow since it makes things easier to access.

Now go and get this plug. Which despite the 1.5" description will fit nicely in the 2" elbow. I'm no plumber, I can't explain it.

Should fit together for something like this.

Now go to your favorite auto supply store and get a tire valve stem. You are going to drill a small hole into the 1.5" cap so that you can stick the tire valve stem through it.

* Alternatively you can install a compressor fitting into the cap that you can attach to directly to your home air compressor line. However you will need some sort of regulator on the air compressor.

You should now have a boost leak tester that looks like this:


Things you will need:
A squirt bottle with a soapy water solution in it.
A source of compressed air with a gauge on it. (See my next reply if you don't have any access to compressed air)
Zip ties. (Used on vacuum lines that are leaking)

You can now attach your new boost leak tester to your turbocharger inlet. You will also need to block some lines in order to get the best results. Block this guy so that air cannot escape out of the valve cover:

And block your pcv hose.

Now you need to use your air supply to raise the air pressure inside your system to 2-3 psi above what your turbo currently makes. I use a tire pressure hose to raise the pressure, and the gauge mounted on it to tell where I'm at.

Now listen for leaks. If its a big leak you can feel it with your hand and tell where its coming from, but if not, now is when you spray your soapy water solution. When you see bubbles, there's a leak there. Now the pressure will automatically drop slowly over time do to air leaking past the throttle body, piston rings, valves, etc. But it should take 30-60 secs for this this to occur. Usually when leaks are present this pressure drops much more rapidly.

I've had leaks from anything from vacuum hoses, to boost tubes, to injector o-rings. The more thorough you are, the better results you will get.
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Brag's Ghetto-tacular method of getting compressed air for your boost leak test:

You will need to buy a 2-5 gallon air tank:

And a small air compressor:

These can both be purchased from your local auto parts store for little cash. Some air compressors run on a wall outlet, and some can run from your cigarette lighter.

Essentially you want to get the air pressure in the tank up to 40-50 psi using the small air compressor. Then hook the tank up to your boost leak tester. This will not last very long, and won't get super high pressures, but back in the day in was the only way I could do a test since I didn't have any access to compressed air.

If someone has a simpler/cheaper solution for this, I welcome it.
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or if ya dont wanna make one, VotionSpeed has'em.

example, Turbo Intake Leak Pressure Tester - 3.0" Blue
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Shop at Home Depot hahaha Sorry I work in the plumbing department personally and have thought about this. You could also just get a rubber cap and put a valve in it with a hose clamp and pump it up... Should be able to hold 30psi atleast...kind of like whats the pic above just make sure it will fit 2.5 ID pipe

Working at Homedepot I also made the sickest beer bong out of 6" PVC with a 6" T in the middle and 2, 6" caps on the end.. It will hold 1/2 a keg and had 6 lines comming off of it. It is 4 feet long just the sickest thing ever hahaha

Hey OP you need more pics of this in action...
im actually a plumber. there is a fitting that sells at plumbing supply shops ( **** depot does not ) it has a 1/4" port for an air gauge, here is it

it has a 3/4 fip end on it.
use a 1 1/2" spigot x 3/4 fip fitting

and an 1 1/2 fernco from **** depot or the same place you bought the other fittings. chances are they have it there as well. it looks like this.

cap the other end with a gem cap.
looks like this.

pump it up and let it sit for 10 minutes, the pressure will drop very fast if you have any leaks.
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PCV will work as well and a big ole compressor to pump it all through
you dont need a big ol compressor. just hand pump it. should be pumped up super easily with just a hand pump. ive pumped up whole underground plumbing with just a hand pump and its not that difficult. the soapy water comment is actually a commonly used method and works great. but even with a whole house full of plumbing any leak will cause the gauge to fall pretty rapidly. any leak in charge piping will be much more apparent because of the lack of volume. the lack of volume is also why it should be a cinch to pump it up very easily with a hand pump. compressor might blow something
The big ol pump was more of a joke I have used large compressors I would think that my little 7gal would do the trick as well never used a hand pump but I might give it a try just for shits and giggle plus its way more portable than the little electric one.
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