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Discussion Starter · #1 · (Edited)
Yes I have searched, as well as consulted a few experts, including Lucky from ARD & a good friend who is a tech for Audi. My car will not boost beyond about 12 psi. I am running a 17 psi ARD tune. No matter what I do, I can't get past this 12 psi. I have tried a lot and so far I have only got an extra psi or two, how I got to ~12. I was trapped at closer to 10 psi for a while. All of this has happened over the past few weeks. I need to find the solution, and I do not want to just throw expensive parts at it as a method of trouble shooting. I need ways of testing & troubleshooting. I will try to give the short version of the facts, I hope someone can shed some light.

Car is a 96 855 T5, ~130k miles. Idles perfect with vacuum around -22 at idle in park or neutral. The boost holds steady, just not at the right psi, so I doubt its a leak. But I have changed a ton of vac lines & the coupler from the turbo to the pipe that goes over the top of the engine with a silicone one, as well as any clamps that looked questionable. But again, boost is steady, but not at the right psi.

Before getting the ARD ecu, I added a MBC and upped the boost to about 10 psi, and the car felt good and as it should have. I then got the ARD ecu with the 17 psi Green tune. I installed that and upped the boost on the MBC to about 15 psi. At this point, I was hitting 15 or so, but with a rapid fall of to about 10 psi. Switched back to stock BCS and it spiked at ~11-12 psi and dropped still to the ~9-10 psi. This is where I have been stuck.

So I searched and spoke to Lucky trying to figure out what was causing this. Possibilities were: a bad BCS, a bad wastegate actuator, or the cat being clogged and causing a massive flow restriction. The MBC now will not go higher than ~12-13 psi either, even with the BCS capped, so its not the BCS. I also did a test Lucky recommended of tying the wastegate shut, with the actuator rod off, to see if it would even want to boost higher then, and it still didn't. This was what made me think the issue was “after” the turbo, and this is when I removed the cat.. I also saw a post about the wastegate flapper not sitting correct, so I checked that too.

Not only do I need a solution, but why was I able to hit 15 psi for a bit and now can't even do that with a tied wastegate??!??
 

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Discussion Starter · #2 ·
Oh, and sound wise, it doesn't make any noises that would indicate a blown CHRA. With no cat & a cone filter, I would hear it, I have heard blown turbos before. And also speaking of sound, it doesn't even sound like its trying to build more than 10-12 psi, as far as spool sound. So I really doubt a leak. Also way too steady of a hold (at the wrong boost) to be a leak. In my experience, leaks are more erratic.
 

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seem to remember a similar thing a few month ago, have you gotten a new external dumpvalve? Im still a bit fuzzy on all the acronyms, but as far as I remember, dumpvalve had a bad spring, causing it not to hold back psi, but let it out in the atmo, wihtout any vacuum.

i dunno, Im more of an NA guy anyways.
 

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Discussion Starter · #4 ·
CBV is the Compressor Bypass Valve, aka dump valve. And the spring in it is my suspect now. Wanted to see who also had issues to see if I am missing something else.
 

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guy I was talking about, had the same problem in his S60 2.0T, after mapping and stuff, he had about 340hp and a Forge CBV, spring didnt behave as expected, so whenever he hit about 1bar boost, CBV started flapping and let all the boost out.

get a new tighter CBV spring, and take it for a mapping, let them figure out what the problem is, and how to correct it.
 

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cvb, wg or mbc.
 

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Discussion Starter · #8 ·
Frustrations continue, as my problem continues.. I still can't get this working right. After changing a million things and basically no improvements, I am almost fed up and ready to sell the car and cut my losses. Most recently, I bought the Mitsu CBV rebuild kit (new diaphragm, spring & the thing that holds the spring) and replacing basically ALL vac lines. Including all the ones to the wastegate, compressor housing, CBV, the line from fuel pressure regulator to vac tree, and replaced the caps on the vac tree. I removed the cat & had the exhaust leak fixed. I also added clamps to the hoses for the IAC valve, replaced a few intercooler hose clamps. Also went back & forth from air box to cone filter. I cleaned the MAF with MAF cleaner. Went back & forth from stock boost controller & mbc. Replacing the CBV did seem to help and be necessary, and the noise after throttle lift-off changed from a chatter/flutter (almost like compressor surge) to a solid "psshhhh".. Still, I have yet to see 17 psi...


With the MBC I can sometimes see ~15psi with a pretty quick fall off down to ~10psi. Sometimes I don't even see the 15 psi, I only go to the 10 in the first place.. And sometimes when I do see the higher boost, it doesn't even feel faster. With the stock boost controller, I rarely see higher than the ~10 psi. Sometimes ~12-13 if I floor it in 4th on the highway in "Econ" mode to prevent downshifting.


Tomorrow I will be replacing the plugs with some NGK BKR6E Coppers. From what I see I should gap them to 0.026, correct? The current plugs are OEM Volvo, unknown age. They look worn but not covered in oil or bad tips. Just some yellow/whitish on the tips. I will also be changing out the 2 remaining intercooler clamps that look so-so, the lower one to the intercooler itself. They don't look loose, but they are quite rusty.
 

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Discussion Starter · #9 ·
Thought I would update to those that posted & future searchers. It was the wastegate actuator! With the MBC it now holds an impressively steady boost!!! I may have an issue with the stock BCS/TCV but thats easy to diagnose, since it holds great with the MBC. I have had the MBC hooked up, I will revisit the BCS/TCV this week.
 

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so it was bad? or just needed to be adjusted? I'm having the same issue in my 95 855... got an ARD green tune.. was at 17PSI on factory turbo. Upgraded to a 16T and now won't get more than 12psi. turbo came with a new wastegate... so I'm wondering if I need to adjust it?
 

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Discussion Starter · #11 · (Edited)
No it was not just an adjustment. I adjusted the stock one til it bottomed out and still sucked. After removing it, I realized it took almost no pressure to pull the rod out. The spring inside must have failed. The new one is much tighter and holds rock solid boost with the MBC.
 

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Discussion Starter · #13 · (Edited)
There's videos (IPD) and how to write ups on adjusting the rod. Its easy. Try that first. Otherwise, I got a sick deal on a brand new unit for like $50 shipped, and they offer a variety of psi settings.

This is the other reason I changed mine. Everything else under the hood is quite clean, but the WG Actuator looked AWFUL!


 
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