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Running M4.4 DIY tune in the 855 T5 for awhile now.  About a year or more ago I had the head off for a valve job and new valve guide seals.  Got it back together and been running for more than a year since.  Oil consumption went to almost zero, so that's good.  Compression is decent but not great; 145-155 psi range.  The car runs great, but..

Over the past year or so been through a lot of life transitions so haven't been able to really look at the tune until just recently, in the last few weeks.  Gone back to the basics running 607 rev5b w/mods for green injectors, bigger maf, re-scaled max Load moderately (to about 12 or so ms).

What's puzzling me is that I'm not even getting close to being able to hit higher loads or boost (18t).  Load seems to be peaking around 7-8 ms and boost peaks about 8-10 psi.  Like I said, it runs well, but not a good as it should.  The TCV is maxed out at 99% duty cycle early in the boost cycle and stays there (until throttle is backed off).  So it's trying to create more boost, but apparently can't.  Going to start looking for boost hoses leaking and things like that, but all appears to be in order and it idles just fine (i.e. no noticeable vacuum leaks).  And no knock what so ever!  On boost AFR is around 12, ignition timing is in low teens.

Am I missing something else in the tune maybe that could be doing this?  Like I mentioned, haven't been actively tuning for over a year so I'm rusty; maybe I'm overlooking something stupid?  :a-farmboy:

TIA for any suggestions.

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Posted (edited)
13 hours ago, Midnight Caller said:

Hello ! Did you check the CBV în the turbo or is it blanked ? They are prone to membrane cracking and the effects would be quite like in your description

^^ Thanks much MC!!

That could definitely be it.  Tried it today and mine will not hold vacuum. 

But I've got an old 15G on the bench and it won't hold vacuum either.  The CBV diaphragm in it is old but don't see any tears/holes?  Are they really supposed to (hold vacuum)?  It appears to have a bleed hole in the center of it.

The one in my car is from IPD and was replaced some years ago (last time I had the turbo out).

Edited by gdog
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Well, I checked mine by connecting the boost gauge to the CBV instead of the vacuum tree at the intake manifold. Of course I didn't exagerate with the throttle, but seeing the boost gauge start to rise at half throttle acceleration definitely told me something was wrong. So I've put a blanking plate and a blow-off valve and solved the problem.

The CBV is supposed to let the excess air out of the turbo back to the air filter when vacuum is applied to it (throttle plate closed quickly). In normal acceleration, you have positive pressure on that hose.

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Pretty ingenious way to test CBV!

With that, and after staring at the one on my bench for awhile, I see that it indeed should hold vacuum.  The can on my bench turbo was warped a bit; straightened it out and now it seals (and holds vacuum).

New one from IPD on order.  I think I used the blue spring last time; will go with red spring this time!  :tongue:

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Hopefully that will set things straight :)

I can't forget the day I removed all my fuses în my old V40, and when I put them all back the aftermarket CD player didn't turn on when starting the engine. Ripped it all out, chcked everything in the board, and couldn't find anything wrong with it.

Put it back in and out of reflex pushed the "ON" button. What do,you know, it powered on :))) It just resetted itself.

Amazing how our brain sometimes looks for solutions in most complicated ways :))

 

 

Edited by Midnight Caller
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Posted (edited)

Bummer; new CBV is installed, but boost pressure is no better.  It appears the CBV can was over-tightened, hence it deformed so it would not hold vacuum.  But vacuum only assists opening it at over-boost conditions so should have figured that wasn't the issue.

Looked around and didn't notice any torn or damaged hoses.  Will have to do a more thorough inspection once I have long term access to a work-area or garage.  Have a sinking feeling there's a hole in the intercooler; oil seems to be accumulating on lower passenger side of engine bay where there really aren't any oil lines.  If that's what it is, I'm hoping it can be repaired; another do88 intercooler ain't in the budget right now..  :unsure:

Edited by gdog
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20 hours ago, ChristiaanW200 said:

did you check the tcv valve? 

 

what happens when you disconnect the yellow or red hose and then accelerate? (with care afcourse)

Good question.  But ard TCV appears to be working correctly; tested in driveway with jumpers:

  1. no pwr applied to tcv: open between port 3 (compressor housing) and port 2 (WGA).  This allows boost pressure to be applied to WGA (PWM modulated by TCV)
  2. 12v pwr applied to tcv: closed between port 3 and port 2

And even took a test drive w/compressor housing vac hose (green hose in this diagram) clamped shut; no difference in boost levels.    :sad:

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On 3/19/2021 at 5:58 PM, gdog said:

Good question.  But ard TCV appears to be working correctly; tested in driveway with jumpers:

  1. no pwr applied to tcv: open between port 3 (compressor housing) and port 2 (WGA).  This allows boost pressure to be applied to WGA (PWM modulated by TCV)
  2. 12v pwr applied to tcv: closed between port 3 and port 2

And even took a test drive w/compressor housing vac hose (green hose in this diagram) clamped shut; no difference in boost levels.    :sad:

please disconnect the hose to the wastegate and verify. even a little leak on that clamped can have effect. 

 

if you dont have any boost then. then it is a mechanical problem. exhaust leak (would be quite noticable), incorrectly adjusted wastegate (did you check this? ) or defective turbo (burned wastegate valve/housing or turbine wheel). 

 

good luck testing

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1 hour ago, ChristiaanW200 said:

please disconnect the hose to the wastegate and verify. even a little leak on that clamped can have effect. 

 

if you dont have any boost then. then it is a mechanical problem. exhaust leak (would be quite noticable), incorrectly adjusted wastegate (did you check this? ) or defective turbo (burned wastegate valve/housing or turbine wheel). 

 

good luck testing

Yes I did check the WGA adjustment while I was in there and it is adjusted properly for the ard WGA.  Is a burned waste gate or turbine housing likely?  The hot side is a kinugawa 17cm angled bought new probably about 5 years ago.

Next time I go for a drive I will pull the turbo hose off and clamp it, but I'd be willing to bet it's not going to make a difference.

Plan is to pressure test the intercooler this week some time, and if that's good, will look further.  Inspecting the turbine and waste gate will require turbo removal which is a bit more work..  :sad:

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if you have a hole in your intake system that is that big that you dont hear it or loses that much air, its a pretty big hole. unhook the maf, and block of the intake with the engine running. if it stalls, there is no hole big enough to cause this. 

 

wastegate is easy, just unbolt the downpipe from the turbo and inspect with a mirror. 

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Update: pressure checked the intercooler and thankfully it was good.  Did find a significant leak around the bottom intercooler hose, but a new clamp resolved that issue.  Tested it to about 25 psi and held pressure after that.

But that still didn't fix the boost issue. Even tightened the WGA one turn to make sure it's hard up against the closed stop position.

Wanted to do one more test before pulling the downpipe; check the cat convertor.  It's aftermarket and it has about 40K miles on it; from what I've read these only have a 25K mile warranty.  Tested pressure upstream and downstream of cat (via the O2 sensor bungs) and sure enough the cat seems to be clogged.   Got up to 6 psi upstream (when on boost) and 0 psi behind the cat; ideally should 0 at both ends but have read that 1 or 2 psi upstream may be acceptable.  I.e. with that much back-pressure it's no wonder I'm not getting expected boost pressure.

Cat test pipes seem to be contraband now, and I don't weld (:sad:) so I guess I'm shopping for a cat and a local shop to install it.  Let me know if you guys have recommendations/suggestions!

If interested, you can see photos of my exhaust system here: https://volvoforums.com/forum/volvo-850-16/obx-exhaust-system-improved-76767/

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  • 2 weeks later...

Well looks like I had multiple issues here, but the primary one is what @ChristiaanW200 mentioned; got the downpipe off today for a look-see and holy-sh*t!!  The hot side suffered a melt-down that looks like something from Chernobyl!!?  The poppett valve looks OK but about a 1/3 of its seat is missing!  Couldn't get enough of a look to take pictures but turbine wheel appears OK.  Will get a better look once I get the hot side off, but need to get another housing first.

Are kinugawa parts decent?  This one was new about 5 years ago.

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