Author Topic: Intake leak test (how-to)  (Read 8640 times)

Offline mattias

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Intake leak test (how-to)
« on: October 19, 2010, 01:51:41 pm »
Intake leak test
It can be a very good idea to make an intake leak test on any engine, regardless if they are using forced induction (boost via turbocharger or crank driven compressor) or just naturally aspirated.  You can find a lot of things wrong that will affect  the tune and calibration of the engine, here are a few things :
  • Leaking intake gaskets
  • Fuel injector O-ring seals gone bad (crispy rubber, corroded aluminum)
  • Leaking pressure signal lines
  • Blown wastegate diaphragms (bad quality or careless assembly after changing springs)
  • ..

Use safety goggles and gloves to protect yourself in case anything detaches and comes loose hitting you in the eyes, head, hands..
Use ear protection at higher pressures once you are sure it has no leaks at 0.5 bar, at higher pressures you must be careful of your hearing in case anything comes loose.

What to do?
Remove the filter from the compressor inlet, seal the inlet.   It can be hard to avoid the effect of valve overlap with many cylinders, so sealing the exhaust tips can be a good idea to maintain the pressure if you don't have plenty of compressed air, an added bonus is that you will also leak test the exhaust system.

For sealing I recommend a cheap method that almost anyone can use. Take a couple of plastic bags, apply a couple of layers on the inlet you want to seal,  armor the plastic with a textile rag as the last outside layer and then apply a strong hose clamp. This is usually enough to seal the compressor inlet even at super high pressure - much easier than finding something else that can seal the inlet. Of course, if you're able to and not in a hurry you can machine/weld/lathe an adapter if you like and even apply the pressure through a nipple on this adapter.

Now  hold the throttle wide open = WOT and take the signal line that goes to the fuel pressure regulator and pressurize the whole intake system through this signal line. Use an air pressure regulator, which exists on most basic air compressor tanks, and apply 0.5 bar at first, then stepping it up to 3 bar to make sure the system is air tight. You may find that it will leak through the crankcase vent, this is normal and is NOT a sign that your piston rings are going bad.. :)

How to spot the leak
You can either listen for the leaks, the big ones can't be missed.
If you want to find small ones, use soap water in a spray bottle. The bubbles is a dead give-away.

How much is too much
You're looking to eliminate the big wooshing sounds, expect to find leaks and not being able to fix all the small ones. In turbo systems the dump (or blow-off) valve is a prime suspect, it should seal perfectly.  Sometimes small hisses can be an ok compromise - for instance it is quite normal to have air leak past the axle of the throttlebody.

Things you won't detect
Beware of large reinforced rubber/silicone degree bends in front of the turbocharger/compressor inlet. There is a lot of vacuum here at full load on the engine and I've been bitten a couple of time by these collapsing. In a datalog it will look like you've just lost all or a major part of the boost that you normally would have. If you want to try running without a filter to check for restrictions or problems try running with a stainless filter mesh, you can use a kitchen strainer, that will prevent the babies and small birds from being eaten up by the compressor wheel.

Thanks for reading, now go make some more power. :)

« Last Edit: October 19, 2010, 02:42:34 pm by mattias »

Offline fphil

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Re: Intake leak test (how-to)
« Reply #1 on: August 09, 2011, 05:42:22 pm »
Thanks for the tip Mattias. It reminds me I should do it even if the biturbo has a good boost presently.