boost leak test

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boost leak test

Postby CELL_PROTOTYPE_X » Tue Nov 24, 2009 12:24 am

Has anyone on here performed a boost leak test before? I did one the other day on my 3rd gen 3sgte and I think I f'd up. I hooked my tester to the intake side of the turbo with the oil cap off I wasn't able to build any pressure in the system so I stuck oil cap on and it worked...but around 7psi I noticed air leaking from around the valve cover gasket. I read everywhere that you aren't suppose to leave the cap on during the test so I'm kind of worried. Please advise!
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Postby CELL_PROTOTYPE_X » Tue Nov 24, 2009 3:26 pm

nobody has any insight on this?
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Postby ct27gt » Tue Nov 24, 2009 3:33 pm

eh, I have a 2nd gen and left the cap on and no problems for me. Never tried it without the cap.
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Postby CELL_PROTOTYPE_X » Tue Nov 24, 2009 6:19 pm

Thanks for the reply. So I'm wondering if it's ok to leave the oil cap on. If not, how are you suppose to pressurize your system and test for boost leaks? When I tried the test with the cap off I couldn't build pressure :/

My overall issue and reason for doing a boost test is because I don't think my car is boosting properly. The car sounds like a jet when it starts building boost and it hasn't been pulling like it used to :/ Big sound but little bang
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Postby Dups90gt » Tue Nov 24, 2009 9:03 pm

I did a boost leak test last year with the cap on, just dont go over you set boost limit or you'll blow something (say 12 psi or 10psi) I have the same problem with lots of noise and not much pull, I swapped in a ct20b but havent had time to fix the wastegate or do a proper leak test.. too cold now..
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Postby CELL_PROTOTYPE_X » Tue Nov 24, 2009 9:11 pm

Ok cool, so if I'm leaking air at the valve cover around 7psi I should look into replacing the gasket? Doesn't seem like I'm leaking oil though :/ Could a leaking valve cover be the culprit of my lack in performance? Sorry if these are stupid questions...just trying to get to the bottom of my issues :) Thanks for the input
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Postby 3sgt-s » Tue Nov 24, 2009 10:35 pm

You shouldn't have a lot of crankcase pressure first off unless your rings are worn. I would do a compression test and if the numbers are off run a leak down test. Remember to do your tests at operating temp as well.
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Postby tissimo » Wed Nov 25, 2009 2:27 am

Check all your PCV hosing/valves. One is bad or missing if its pressurizing your crank case.
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Postby bridge47 » Wed Nov 25, 2009 12:34 pm

I wouldn't be too worried about valve cover hissing. If its not leaking oil, and if sound is major, look somewhere else. The "jet" sound that you described would indicate a big leak. And when I hear same on turbo cars I've worked on......its loose, cracked(underneath), or disconnected hose connections.

Check with mechanics stethescope or vacuum line up to ear to find leak.

Could be exhaust leak pre-turbo as well, but this is usually easy to spot on a running engine.

Oh....and theres no PCV on your engine(if original).
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Postby CELL_PROTOTYPE_X » Wed Nov 25, 2009 12:53 pm

Thanks for all your input! I'll try the test again and see if anything stands out.
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Postby tissimo » Wed Nov 25, 2009 7:17 pm

bridge47 wrote:I wouldn't be too worried about valve cover hissing. If its not leaking oil, and if sound is major, look somewhere else. The "jet" sound that you described would indicate a big leak. And when I hear same on turbo cars I've worked on......its loose, cracked(underneath), or disconnected hose connections.

Check with mechanics stethescope or vacuum line up to ear to find leak.

Could be exhaust leak pre-turbo as well, but this is usually easy to spot on a running engine.

Oh....and theres no PCV on your engine(if original).


I would be extremely worried about pressurizing the crankcase. Either there is a huge boostleak (bad PCV Valve) or the engine is completely shot.
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Postby CELL_PROTOTYPE_X » Wed Nov 25, 2009 11:51 pm

I know my engine isn't shot...and I know I can't have a huge boost leak because I am able to still build boost while driving plus the car runs just fine. My theory is that I have a small boost leak somewhere combined with incorrect EBC settings.
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Postby 3sgt-s » Thu Nov 26, 2009 2:45 am

Wouldn't hurt to run a compression test just to see how it is looking.
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Re: boost leak test

Postby Rallly » Tue Jun 07, 2016 12:24 am

I want to do a boost leak test. Do I remove intake hose and filter box off turbo and block turbo coupler(battery side) with soup can?, then feed air into the intake manifold??
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