I have a bad and very elusive boost leak and am having a hard time pinpointing it. YES, I have searched and read every write-up on here and still have some questions, so please don't just link me to the threads I have already read. Sorry this is really long but it's a little complicated.

Here are the basic facts:

- I have leak tested from the turbo to the TB, but not past the TB. This is because I didn't know to use the marks on the cam gears to find TDC, and gave up on trying to turn the engine "blind in the dark" to get the valves as closed as possible. BTW this seems to be the single most important, and also most omitted step in how-to and other boost leak testing threads/links/discussion.

- With the intake tract from turbo to UICP/TB verified leak free to 28psi using a compressor and tester, there is still a very bad, and quite audible leak under only the following circumstances:

A) When the car is significantly hot. Not just "warmed up", or gently driven around this cold time of year for up to an hour, but HOT from being driven hard for more than a few minutes straight i.e. a lot of time at WOT and upper RPMs.

B) At 5500+ rpm in third gear or higher, and sometimes not even third, but definitely 4th and 5th.

Under these circumstances, boost barely spikes to 18-19psi, then tapers all the way down to 5psi or so as it reaches redline, and the leak can be heard quite clearly at this time.

This leads me to suspect that it may be the infamous TB shaft seals, and/or the injector seats. A lot of the more common loose/disconnected hose etc. culprits don't seem to be likely, since the leak would be happening all the time, and not just under the specific circumstances I mentioned. I plan to do a full leak test past the TB into intake manifold and head, and while I am at it will probably replace the TB shaft seals and maybe injector seats just for good measure. I know I need to plug the boost "signal" line that goes to the MBC.

My questions are:
- Even at TDC, won't some pressure still leak out through the valves?
- Besides the TB shaft seals and injector seats, what else could it be that surfaces under these conditions? What other leaks will only surface due to HEAT and HIGHER AIRFLOW? Intake manifold gasket? Seems highly unlikely.
I want to address everything possible at this point, to make sure I can get this solved for once and for all.

Thanks for reading all that. If you have some insight from experience please let me know.

 

no one?
I guess that mean I should just get the TB shaft seals and injector seats?

 

check for it. clamp hose and gapping on your car. or buy boost like device.

 

Did yo read my first post? I already have a leak tester, and already did a leak test up to the TB. I'm just asking if there is anywhere else besides the TB shaft seals and injector seats where it could be leaking from under those conditions.

 

have u tried spraying water w soap on it and seeying it if bubbles????

 

check you 02

 

the O2??? as in the 02 sensor/bung in the O2 housing? if that's what you're talking about, that's on the HOT/exhaust side, and has nothing to do with a boost leak.

i guess i shouldn't ask for advice until i actually pressure test past the TB and head. i just wanted to go ahead and replace every possible culprit as a sure shot way to fix it.

 

You can tell TDC by taking off the can gear cover and match the cam marks with the valve cover marks. Is it spiking and dropping off fast or just not hitting any higher than that?

 

Thanks for posting revmoto.
It's spiking, but to a few psi lower, and for a shorter time than when cold/lower gears, then tapering off VERY quickly and badly down to like 5-8psi compared to lower gears/when not really hot.

 

What BOV are you running?

 

Undeadmonk, are you on drugs?
Hokiruu, like Rev. suggested, line up the marks on the Cam Gear. If your TB or Intake Mani. is leaking, you should be able to hear it externally. If you already tested the rest of the system, you could take off the UICP at the TB only, and test from there. It sounds like the TB seals are your problem, especially since you have a 03.

 

Thanks for the replies.
I'm using a IX metal diverter valve.
I'll test everything again this weekend, at TDC this time.
Like you said, I wouldn't be surprised if it was my TB seals, since it's an 03 and has seen it share of the elements.

 

<p>why are you worried about tdc. that's only for number 1 cyl. not all 4. only thing this I needed for is doing a comp test. Also you checked for boost leaks, have you tried doing a vacuum leak test.</p>
<p>&nbsp;</p>
<p>Unless we have the car all we can do is guess. My guess is t.b. seals.</p>

 

dafarmer, this has been one of my points of major confusion!
whether at TDC or not, won't at least one valve be open? i still am not clear on how people perform a 100% leak test past the TB.

 

same here, I've always wondered about this too?

Some other possibilities for leak sources: if it only leaks when hot, it could be due to metal expanding/contracting from heat. For example a hose-clamp being just tight enough when cold, but expanding from heat to allow a leak when hot. There are t-bolt clamps on the market that use a spring between the nut and the clamp, keeping constant clamping force regardless of temperature. Is it very cold where you live? Definitely check the TB seals first though.