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boost leak cause major turbo lag?

I'm experiencing a pretty bad boost leak at my TB shaft seals. I was noticing the car was taking FOREVER to get up to full boost. I have a TD05 20g turbo but it won't spool up to full boost til about 5500RPMs.
So basically... would a bad boost leak at those seals cause something like that to happen?
I just swapped off a fp t28 for this turbo not too long ago, but the T28 had a crazy fast spool, so the only other thing I considered is possibly bad adjustment on the wastegate actuator rod? I didn't swap anything else out except for the turbo, so it's the only thing I can think of.

I was just wanting some input while I've got the TB out to change the seals.
 

Barnes

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Joined
Feb 9, 2003
Messages
6,249
Location
Richland, WA
I kinda doubt that only throttle body seals would be enough to cause you to lag that much. Is the turbo internally gated?
 

The turbo is internally gated which is why I had mentioned the wastegate actuator rod. I'm hoping that may be the problem. I know that a boost leak could cause turbo lag but I figured that such bad turbo lag had a different cause as well. I'm gonna check out that actuator rod as well.
I just wish I would have checked that out before I installed the turbo.
 

i would say stick with the turbo and wastegate.

Depending on where you got the 20g from maybe they didnt make the gate very well.

Often times the springs are to weak to hold the flapper open under higher boost levels.

if you had a bad boost leak, the car wouldnt spool period, you would be able to get up to rpms high enough to make boost
 

RedTwo

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Jul 16, 2008
Messages
1,917
Location
New Zealand
Have you pressure tested your intercooler system? The other option is a big boost leak around the exhaust manifold to head connection or manifold to turbo.
 

citymunky

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Sep 22, 2010
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1,761
Location
Chesapeake, VA
Full boost at 5500 RPM? I have a 20G also and I can hit full boost in under 4K RPM's, but I have a external WG.
 

Yeah, I've pressure tested the whole system from the turbo to the TB elbow with no leak other than a SLIGHT leak on the BOV flange which I fixed, then the only other leak i've found is the TB shaft seals. And I took off the manifold heat shield and made sure the bolts were good on the manifold to turbo and the nuts were tight on the manifold to head. All good. No leaks that I could find at all.

I actually tightened up the actuator rod on the turbo today by a couple turns to see if that would help at all and it hasn't. The only other thing I just thought of is a bad boost controller. I didn't try to disconnect it yet. That could be an issue still if the boost controller is leaking and allowing some air to pass through and open up the wastegate premature.
Also, I even took off the intake pipe and ran it a bit open turbo to see if it was a restriction preturbo, no difference there either. (I have MAFT blow thru)
I checked the play of the turbo and there was none. Also the compressor wheel seemed to spin pretty freely. (I don't really have much to compare it to though... )
 

Quoting citymunky:
Full boost at 5500 RPM? I have a 20G also and I can hit full boost in under 4K RPM's, but I have a external WG.



My point exactly... I'm still trying to figure out if there's anything else going on. Just trying to exhaust all my options before taking the turbo off. I just don't want to have to mess with that yet again lol.
 

496of2000

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Joined
May 4, 2001
Messages
642
Location
San Diego, CA USA
Did you check the hose from the BOV to intake manifold. Mine was cracked at the intake mainfold, causing slow spoolup.
 

I didn't check that, but I believe I replaced that whole hose when I was cleaning up my vacuum lines. Also, I probably would have detected that when I did my boost leak test. Then again the TB shaft seal leak is so bad I didn't even notice the BOV flange leak til I sprayed some soapy water there. I'll check it out tomorrow. Thanks for the suggestion!
 

Ian M

Well-known member
Joined
Jan 11, 2002
Messages
2,348
Location
Martinsburg,WV
I'm guessing the car spooled fine with the other turbo and those leaky seals?

I seriously doubt the TB shaft seals are the culprit. I've split the welds on the endtanks on my white car bad enough that when I pressure tested it,it could probably blow a candle out near the front of the car. Not long after I bought my green car,I had a dime size hole blow out from a shoddy IC weld that a previous owner did. Niether of those major leaks did the car spool really much slower,just hit softer and the power was off. I've never felt a TB shaft or BOV flange leak make THAT much difference.


I'm also thinking pre-turbo exhaust leak,or the wastegate is hanging up or isn't closing all the way. Is the turbo/exhaust housing new? Does it spin (now that it's on the car) without binding? On older turbos I've also seen the bushing where the WG flapper pivots work it's way outwards causing the flapper to not cover the hole completely,or if the hole has been heavily ported,the edge of the flapper catches the hole and hangs open.
 
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