Should air leak into the engine from the turbo inlet with the turbo outlet closed? - Miata Turbo Forum - Boost cars, acquire cats.

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Old 04-21-2009, 12:17 PM   #1
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Default Should air leak into the engine from the turbo inlet with the turbo outlet closed?

If I blow air through the turbo inlet with the turbo outlet closed should air go through the turbo? I'm doing this to test for a boost leak and can hear air going into the engine when I take the oil cap off. I'm trying to narrow down a boost drop off I'm experiencing, thanks!
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Old 04-21-2009, 12:24 PM   #2
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Possibly crankcase vent?
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Old 04-21-2009, 12:34 PM   #3
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not sure what you mean...

well (with an air compressor) I'm pushing 15psi into the turbo compressor inlet and the compressor outlet is closed off...I don't see anywhere else it could escape but THROUGH the turbo back into the manifold and this is why I can hear it through the oil cap. Just want to know if this is normal, because I can't figure out where else my boost would go.

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Old 04-21-2009, 01:16 PM   #4
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If you are hearing it in the oil cap it could also be a faulty PCV valve, or worn/shot valve guides/seals.

Its not going through the turbo and into your valve cover, its getting there from the combustion chamber.
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Old 04-21-2009, 02:08 PM   #5
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you guyz obviously aren't listening [reading]....
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Old 04-21-2009, 02:10 PM   #6
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Air should go through the turbo....

I don't know what you mean about the turbo outlet being closed off...are you plugging it somehow?

If so it sounds like PCV.
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Old 04-21-2009, 02:29 PM   #7
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Let us pretend we have a straw.

and we put our finger on the opposite end and blow through it. somehow you can hear a leak in your *******.

its not the pcv.
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Old 04-21-2009, 02:37 PM   #8
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Quote:
Originally Posted by Braineack View Post
Let us pretend we have a straw.

and we put our finger on the opposite end and blow through it. somehow you can hear a leak in your *******.

its not the pcv.


Damnit, I'm not hustler, there's never a whistling sound from my *******.


I've read the OP a dozen times, and still am not getting it.


Compressor housing has three holes in it:

INLET - has pressurized air going to it for test

OUTLET - blocked off for test

NIPPLE - mine goes to PCV, shouldn't pressurize valve cover (where oil cap is) unless valve is bad right?


The only OTHER way I can possibly fathom that air is getting into the motor is a bad CHRA seal. I don't know much about this(never taken one apart like you badasses), but I guess it could push air through oil drain line or into the exhaust mani. If so that means serious probs OP, like rebuilding your turbo.
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Old 04-21-2009, 02:45 PM   #9
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why would your boost source nipple go to the pcv?


although i did forget about that guy.
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Old 04-21-2009, 02:46 PM   #10
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My vote goes with blown turbo. Air leaking past the compressor seals, into the oil lines, along the oil pathway, and out the head. I think that would do it...
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Old 04-21-2009, 02:48 PM   #11
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Quote:
Originally Posted by Braineack View Post
why would your boost source nipple go to the pcv?


although i did forget about that guy.
Nevermind. I went out there and looked, that nipple (for PCV) is BEFORE the compressor inlet. Boost source goes to wastegate canister.

That's what I get for lurking (and worse, posting) while studying. It keeps me motivated though.




So blown turbo is the only way air is getting anywhere then?
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Old 04-21-2009, 02:52 PM   #12
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The turbo is brand new (well it sat in a box for 7 months or so before I got it installed)-came from Begi-less than 1000 miles on it. Compressor nipple is plugged-I'm getting my boost signal for wastegate from intercooler piping just before TB. I'm doing all this because I have a boost droppoff above about 7psi. I've had the intercooler piping all apart to test for airtightness with about 15psi going into it from my compressor. Only air I can detect leaving the system (with my IC piping closed off/air tight/disconnected from the TB) is through the turbo somehow because I can hear it when I open the oil cap. I sure hope my 1000 mile turbo doesn't need a rebuild!
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Old 04-21-2009, 02:56 PM   #13
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You're telling me you have:

INLET pressurized

OUTLET capped "or blocked off"

NIPPLE capped

and you're getting air through the motor?

I'm with brain on this one...loose *******.


Trying this one again:

What do you mean by compressor outlet blocked off?
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Old 04-21-2009, 02:57 PM   #14
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i had the same issue when my compressor began to leak but i had to clock my **** and its a mitsu turbo not sure about your garret ****. Could be a loose whatever holds your compressor housing on or dirt matting surface.
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Old 04-21-2009, 03:09 PM   #15
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I don't really have my compressor outlet blocked or capped off-I still have my intercooler piping connected to the compressor outlet but there are no detectable leaks in my piping and it's not connected to the throttle body-instead blocked off at the end of my piping (and IAC valve). MBC is disconnected FYI. Fact remains there is air getting into my engine somehow and the only place I can see it getting there is through the turbo center housing. I'm trying to determine if this could be causing the problem I'm having with boost droppoff-meaning while I'm driving if instead of the boost air going into my TB/intake manifold it's bleeding back out "the back" of the turbo. I will say when I did my test the turbo was cold. But all I've read about finding boost leaks does not mention any air leaking as I'm experiencing (through the turbo). Most people just hook up their compressor/pump to the turbo inlet and test that way. I'm doing this in two pieces: 1)blocking off the intercooler piping at the TB to eliminate post TB leaks 2)I'll get to the post TB leaks after I get the pre TB sorted out. Thanks

Also, I'm assuming if there is a problem with the centerhousing there would be oil inside the compressor housing and getting into my intercooler piping off the compressor outlet, right? So if I look in there and see no oil then should I just not worry about the air I'm hearing escaping through there?
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Old 04-21-2009, 03:29 PM   #16
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Ok, now I get a clearer picture.


Still has me stumped though. Like you said, turbo shouldn't be going bad.

If it was a mating surface issue, boost would leak into atmosphere, not into engine.

I don't know why, but I keep going back to oil drain. This probably wouldn't put oil into intake tract, but could put air into crankcase.


DISCLAIMER: I have absolutely no knowledge on CHRA internals, besides some recent research into journal bearing lubrication minimal pressure and the imaginary "wash out" phenomenon. Will do a write-up soon.

I didn't look at the plumbing, so this is a wild *** guess as to how air could get from compressor, into CHRA and to oil drain.
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Old 04-21-2009, 03:55 PM   #17
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The only other thing I can imagine (IDK how possible it is) is if somehow the turbo is spinning backwards during your test, causing airflow back into the cylinders from the exhaust side and up through some bad valve seals or or guides and out of the oil cap opening.
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Old 04-21-2009, 04:02 PM   #18
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Quote:
Originally Posted by RotorNutFD3S View Post
My vote goes with blown turbo. Air leaking past the compressor seals, into the oil lines, along the oil pathway, and out the head. I think that would do it...
If the OP does have the turbo outlet closed as this answer implies, then I agree with the above poster.
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Old 04-21-2009, 04:16 PM   #19
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Are ther not alwats valves open at any given time? If so wouldn't that be how the air is getting in there? And therefore no pressure will build in the system with the oil cap off?
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Old 04-21-2009, 04:18 PM   #20
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Quote:
Originally Posted by 1redcanuck View Post
Are ther not alwats valves open at any given time? If so wouldn't that be how the air is getting in there? And therefore no pressure will build in the system with the oil cap off?
Valves, even when open, don't allow air into the cam area unless the valve seals or guides are bad.
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