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Thread: Boost Leak Testing - How and Why

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    Boost Leak Testing - How and Why

    I provided a writeup that explains the how and why of boost leak testing. It seems that many are unclear on all the details and rationale of this important test. I developed this protocol specifically for the Mitsubishi EVO community, but the same steps, strategy, and reasoning applies to any turbocharged vehicle:



    PURPOSE

    The quickest way to rob an otherwise healthy turbo engine of performance is to introduce a pressure leak within the intake system. The more complex and segmented the intake system, the greater the statistical possibilities for a leak to occur. One thing Iíve realized in dealing with Mitsubishi EVOs is that at least 2/3 of them seem to be running the roads with boost leaks that need attention. Boost leaks tend to go unnoticed until or unless one conducts a boost leak test, which should be done sooner than later. Until the leaks are remedied, there will be some degree of reduced compressor efficiency and power, higher intake air temps, slower spool characteristics, and tuning irregularities.

    Every turbo car owner should test for leaks periodically, and especially after any time a piece of the pressurized area is removed for service, etc. Checking for boost leaks involves a simple pressure test of the intake system. So long as one has access to compressed air source, only a few simple tools are required.


    MATERIALS

    Compressed air source
    Spray bottle with soapy water
    Pressure regulator with male and female quick connect fittings
    Turbo compressor pressure cap
    Means of sealing open lines and fittings (rubber caps, plugs, etc.)
    Hairspray (pump bottle)






    Inexpensive pressure regulator with quick connect fittings - try better auto parts stores




    PROCEDURE


    Step 1

    The entry point of the turbo must be made accessible and pressure tight. This is done by disconnecting part of the intake system from the entrance to the turbo and fitting a short section of silicone adapter tubing to connect the pressure cap to the turbo compressor. Many aftermarket intake systems use a silicone reducer to connect the intake tubing to the MAF. If you donít already have something like this, get one appropriately sized to fit your turbo.



    Silicone reducer




    The turbo pressure cap consists of a piece of aluminum tubing with one sealed end. The one Iím using is a 3Ē diameter piece that fits snugly into the silicone adapter. There is a quick connect fitting on the sealed end and a rolled lip on the open end. A good fabricator can put one of these together. The one I am holding in the photo comes from MP Fab.



    3" turbo pressure cap




    Some turbos do not have a rolled lip at the compressor flange. This usually creates a slippage problem when conducting a boost leak test that results in a loud, startling pop. This can be almost entirely eliminated by applying hairspray around the flange with your finger, and using 2 hose clamps to secure the silicone adapter to the compressor flange. We want to be able to conduct the test with at least the same boost pressure that we expect to use in the real world, and that requires very secure connections.



    Turbo connections must be pressure tight. It's not as easy as it seems.




    Step 2

    You need to trace the intake system from the compressor outlet to the intake manifold, being mindful of any pressure signal taps that lead to something that would bleed air. Be sure you can identify each and every tap into the intake system. If any of these are open-ended, they should be sealed for the test. For example:

    - A manual boost controller is effectively a controlled pressure leak. The boost signal line should be disconnected from the manual boost controller and plugged.

    - A water or methanol injection system should be fitted with a normally closed solenoid valve in the injection line. If not, there will be an uncontrolled pressure leak that aside from being a source of leakage for the test, can create pump priming issues when the engine is in operation. Be advised.



    Solenoid valve - a good idea




    - If there is a recirculating blowoff valve, disconnect the recirculated air line from the valve.

    - The PCV valve can be checked by disconnecting the PCV valve from the cam cover itself, leaving the other end connected to the intake manifold.

    Anything that bleeds air during a boost leak test also bleeds it under real world conditions, so keep that in mind.



    Step 3

    With the aforementioned lines sealed and the pressure source connected, we are ready to slowly introduce pressure into the system. Gradually increase the pressure to 20 psi, constantly watching that the silicone adapter is not slipping. If it begins to slip, prepare yourself for a loud, annoying POP!



    Be slow with the regulator valve. It takes several seconds to pressurize the system.




    With 20 psi in the system, make the following checks:

    - Spray ALL tubing connections while watching for bubbles and listening for hissing. A few tiny, foamy bubbles that slowly seep from joint are acceptable. Larger bubbles that rapidly form and pop are indicative of a leaky joint. Where a leaky joint is discovered, disconnect and carefully reconnect the joint. Doubling the hose clamps is an inexpensive way to make more secure connections at potentially leaky joints. If this is the first time the system is pressure tested, it is wise to get under the car and check the LICP connections. The best way to do this is to conduct the test with the car on a rack with the undertray removed.



    Spray all coupler seams.




    Tiny, slowly oozing bubbles are ok.




    - Spray the IC where the core meets the end tanks. Look for bubbles and listen for hissing. Some IC cores can be leaky, and that is a problem that involves removing the IC and possibly the end tanks to bolster the core end seams with epoxy.



    This is easier to do with the front bumper cover off.




    - Run your finger along the backside of the turbo compressor cover. If you feel a jet of air, from either the cover seam or at the head of a cover bolt, be prepared to remove the compressor cover and reaffix with a bead of gasket sealer (e.g. Permatex gray). This is a common problem with newer Garrett turbo covers.

    - Check that no air is being vented from the blowoff valve recirculated air line. If there is a leak, the valve needs either adjustment or replacement. If there is a VTA valve, check for a leak at the dump.



    No air leak here!




    - Check the open cam cover end of the PCV valve and verify that no air is being vented. If there is a leak, replace the PCV valve without delay.

    - There may be audible hissing at the throttle body. One cause is air passing through the idle air control valve. That hiss should change in tone or almost disappear if the throttle plate is opened manually.



    Hiss is silenced with TB movement




    - Check the throttle body shaft ends for air leaks. Itís not easy to get a perfect seal here, but whistling jets of air that blow large bubbles are unacceptable. If it is a well-used factory throttle body, consider replacing the shaft seals.



    Check for leaks here.




    - Check the injector seals for leaks where the injectors mate to the intake manifold runners. A leak at an injector means the o-ring should either be checked and re-seated, or replaced.



    Look and listen carefully for leaks here.



    - If your vehicle is EGR equipped, check that pressure is not being leaked through the EGR valve. The EGR system should be pressure tight when under boost conditions.


    CONCLUSION

    When you are satisfied that all is well and any leaks have been fixed, very slowly turn the pressure up to at least the anticipated real world boost pressure level, and listen to all parts of the system carefully for any new sounds or leaks as the pressure rises. Most leaks (especially large ones) are exposed at low pressures, but some donít show up unless there is considerable pressure in the system, which is the worst possible time to have a leak. Make absolutely sure the blowoff valve is air tight at the maximum pressure.

    If youíve discovered a large leak or several small leaks, be advised that once they are fixed, you may find that some tuning adjustments may need to be made, especially with mass air systems. This is why it is always best to pressure test your system before the tuning session Ö unless you donít mind taking a chance on having to tune it twice.

    Ted B.
    2003 Mitsu EVO VIII - 2.0L / 600+whp
    1988 BMW M3 turbo - Work in progress. . .
    1986 SVO Mustang - Work in progress. . .

  2. #2
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    yup, i mainly find my leaks at the compressor cover.
    1005whp/831wtq little bit of low boost pump gas magic...

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    Thanks for the writeup!

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    This needs to be stickied!
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    SLIDENY

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  5. #5
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    Good guide. One leak I've always had, with two brand new turbos (SPA, and Precision) were leaks into the oil pan via the drain. If that normal? Should I worry? I've been told both ways - no its not normal, and yes it is normal. So which is it! My SC61 has been doing it from minute 1, and still does it (of course).

  6. #6
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    Quote Originally Posted by SecondtoNone View Post
    This needs to be stickied!
    Agreed!!!


    Jmargo if you are reading this please do.
    This is my signature....

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    Quote Originally Posted by SiGmA View Post
    Good guide. One leak I've always had, with two brand new turbos (SPA, and Precision) were leaks into the oil pan via the drain. If that normal? Should I worry? I've been told both ways - no its not normal, and yes it is normal. So which is it! My SC61 has been doing it from minute 1, and still does it (of course).


    bumping this thread, good one.

    Sigma, my old 35r chra would leak horribly into the oil pan causing the oil to bubble. The new one....no bubbling.

    I dont know w a non BB turbo if it should or not.

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    ...a proper bump too.


  9. #9
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    Quote Originally Posted by BadBoostedBmwM3 View Post
    Agreed!!!


    Jmargo if you are reading this please do.
    Geez, you guys are sooooo demanding.

    Might want to add that you need to spin the motor to get the valves closed.
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  10. #10
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    Quote Originally Posted by jmargo View Post
    Might want to add that you need to spin the motor to get the valves closed.
    ?

  11. #11
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    No, it's impossible to turn the motor to a position such that all the intake valves are closed. There will be some seepage past the TB and IAC, but it's small enough not to disrupt the test. Just use a compressor with decent tank capacity, and that will be a non-issue.
    2003 Mitsu EVO VIII - 2.0L / 600+whp
    1988 BMW M3 turbo - Work in progress. . .
    1986 SVO Mustang - Work in progress. . .

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    jmargo is offline Guess who's back ? Moderator
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    Quote Originally Posted by Ted B View Post
    No, it's impossible to turn the motor to a position such that all the intake valves are closed. There will be some seepage past the TB and IAC, but it's small enough not to disrupt the test. Just use a compressor with decent tank capacity, and that will be a non-issue.
    I did this test a while back but IIRC my motor was at a point that all the air was going out the exhaust. I just moved spun it with a few PSI on the guage till it stopped.
    Sias Tuned, Vortech Blown, 3.2L S52...456WHP/360WTQ

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  13. #13
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    That's because the motor was stopped at a point where one of the cylinders was at overlap - a small period of crank rotation where both intake and exhaust valves are open.
    2003 Mitsu EVO VIII - 2.0L / 600+whp
    1988 BMW M3 turbo - Work in progress. . .
    1986 SVO Mustang - Work in progress. . .

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    is there anywhere I can buy the turbo pressure cap without getting it fabricated?

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    After reading this thread I found this:

    http://www.supramania.com/forums/sho...st-Leak-Tester

    I just like to DIY everyhing.

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    Important note...

    On systems with air flow sensors instead or air pressure sensors...

    Boost leaks AFTER the maf sensor will cause you to run lean when not in boost and rich when in boost...

  17. #17
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    I did a little write up long time ago in other board. But I sealed the downpipe as well to get the most acurate reading/possible leak.

    Click here, scroll down.
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    i love.. these pictures..

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    Good stuff, will do.

  20. #20
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    Quote Originally Posted by nine9six View Post
    is there anywhere I can buy the turbo pressure cap without getting it fabricated?
    http://www.frozenboost.com/product_i...9e288ce238490b

    Use coupon code link987 for a discount too.

  21. #21
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    How are you guys pressure testing the intake manifold if at least 1 of the valves on the head is open? Are you capping the exhaust?

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  22. #22
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    I should have mentioned that one can't really expect to do that with a 6cyl engine, simply because one cylinder will just about always be on overlap. You'll probably have to limit the test from turbo to TB, but that is where the majority of leaks occur.
    2003 Mitsu EVO VIII - 2.0L / 600+whp
    1988 BMW M3 turbo - Work in progress. . .
    1986 SVO Mustang - Work in progress. . .

  23. #23
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    I bought my 91 318i and someone had put a emusa turbo the turbo is actually pretty good ans spools up quick but I have not drove my car in a week or so and when I started it I noticed a fluid leaking from where the header meets the turbo I smelld it and it has no smell I thought maybe water? But it kept coming I do not know much about this stuff could anyone help me out please?

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    Dude, you are awesome! Thanks for taking the time to write this post. I made an account just to say that lol

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    Very nice write up. Thanks for sharing.

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