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Overboosting issue on 08 OBXT


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2008 OBXT Limited, 174k miles, 3k on the engine. All stock (VF46 turbo) except for:

* Invidia catted divorced WG DP

* Invidia up-pipe

* Invidia Q300 catback

* DW65C fuel pump

* Open source protune

I just had the tune done after installing these parts, and I think I'm having an overboosting condition. The tuner said it would hit 19-20psi (5 over target) and that WGDC was off. He couldn't get that to change with the tune, and said that it's probably mechanical. He said since I have a divorced wastegate downpipe, I should make sure the divider isn't obstructing the flapper. I saw a small clean spot on the divider when I dropped the DP, so I knocked it down by about 1/8" overall, and about 1/4" around where the contact occurred. I took a log afterwards and saw that it's still hitting 5psi over target. People on the forum seem to stay below 18 on this hardware, so I don't want to hit 19-21 every time I floor it. 

Interestingly, i noticed a similar overboost condition on an older log I took before modding and tuning. This leads me to believe I should just check/clean BCS, wastegate actuator, and associated hoses. I'll put both romraider logs below if anyone wants to take a look.

Log_before: 3rd gear WOT, crappy ebay exhaust and crappy open source tune by previous owner.

Log_after: 3rd gear WOT, mods listed above, ground down wastegate divider, open source protune. 

Log_Before.csv Log_After.csv

Edited by willisdaye
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Check all associated ebcs hoses and the ebcs if possible. Remove the wastegate arm and manually rotate the waste gate (counterclockwise) to check for free/unobstructed movement through entire range.  Check wastegate arm length as it might just need to be lengthened a few turn to reduce boost/open sooner.

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So far I've checked the BCS and hoses. I bench tested the BCS itself and it seems to work well. some of the hoses seem worn, and might not seal well, so I'll replace / ziptie them. I'll check the wastegate soon. The actuator arm unfortunately does not look adjustable, pic below.

20230125_163227.jpg

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That is not adjustable.  I anticipated a double jam nut clip connected by a pin at the wastegate arm and a threaded rod for adjustment. 

 

Check the pill.  Should be installed in vacuum line off tee going to wastegate diaphragm.  Might as well replace all the vacuum hose.  Chances are it has hardened and lost all elasticity.  

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I ran into the WG/divider interference before with Invidia DPs and would have suspected that first. In addition to what you and Mike have already discussed, and since the WG arm looks pressed on to the actuator rod you could apply pressure directly to the actuator to see if the WG opens fully (should be closed to 90 degrees).

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Rick has a good point.  If you have a small hand air pump, attach to the wastegate diaphram and start adding pressure.  I'm having a brain fart and can't recall oem wg spring pressure  (is it 8lbs, 11lbs?).  WG should be fully open above rated spring pressure.  Should not have to ecxeed 12psi.

Edited by m sprank
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I poked around the wastegate today and I think I'm narrowing it down.

The shorter hoses in the 'T' section are actually in pretty good shape, and there's a pill in there. With the actuator arm unhooked, the wastegate moves freely, with a 70 or so degree range. (pic below) You said it was supposed to be 90? The bigger piece of evidence I found is the actuation pressure. It seems to start moving between 5 and 10psi, but it maxes out at about 20, and when the arm is attached and it hist 20 it doesn't open as much as when it's detached and I open it by hand. My pressure gauge was pretty cheap though so I'll benchmark it when I get the chance.

Overall though, It's also kind of looking like the actuator arm is just too short; It has no slack when the arm is attached, as I had to pull it and compress the spring a good bit just to get it back on. Could this actuator be aftermarket / incorrect / busted? It's my understanding that they don't go bad very often. I've already found and fixed other questionable modifications by the PO so I'd almost be inclined to say they installed this shorter actuator in a dangerous attempt at increasing boost. I'm not well versed with what the stock hardware looks like on this car so someone should chime in.

 

 

wastegate.png

Edited by willisdaye
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It’s been years since I’ve worked with a stock turbo setup, but I would expect the WG to be opening a full 90 degrees; otherwise the flapper is partially blocking the flow. Did it feel like it was hitting anything when you were moving it by hand? I’d pull the DP again and verify the full range of motion. I don’t recall if there was some difference in the WG setup of the VF52 that made the divider less of an interference for the WRX crowd, or if the problem was across the board with this DP, but again I ran into the interference before (and caught it before sending the car to be tuned).

Otherwise what you said about the actuator is also a strong clue. Your WG should be fully open at a pressure below your boost target, and yours is not. Some preload on the WG is desirable to keep it solidly shut, but if you are having to really force it then I would certainly dig deeper as this all would contribute to an overboost situation. 

You said it was a stock VF46 in the OP but the engine has 3k miles. Possible they replaced the turbo with an ebay unit or similar with questionable components? Do you see any markings on the turbo to indicate origin? 

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The turbo has VF-46 engraved on the compressor housing. I can put a picture up this afternoon so you can see but I believe it is stock. 

I was hoping I wouldn't have to drop the DP again :( The threads I read about the Invidia DP divider noted that they only had to take off a small amount of material to alleviate the issue. I really knocked the thing down. Plus, I was seeing this overboosting with the previous downpipe too, which was a bellmouth and shouldn't have caused interferance. Before I drop the DP again, can anyone confirm that the max opening angle in the picture I sent looks reasonable?

In the meantime I think I need to get a new actuator. Consensus seems that Kinugawa is a good choice?

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Hey well that’s a good bit of info if it was doing it on another DP as well. Follow the actuator breadcrumbs first and keep the WG flapper on the short list of things to follow up on if need be. I hear ya - it’s a pain to do things twice (or more) when you’re chasing down gremlins. 

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Actuators fail.  It is "rare".  But they do fail.  If you dent the dome they dont work the same either.  Its a pressure vessel so any changes to the vessel or the inner diaphragm change operation. 

 

Just a thought...  If the waste gate is not closing properly, say there is a crack in the housing or the flapper is no longer correctly sealing then the tuner would be adjusting the boost targets unaware of the "leak" unless they notice how much extra they have to push.  Then, as the flapper opens you could be over boosting.  Long shot, but I can see situations where the circumstances are just right.  If everything was perfect from the start a flapper leaking would be very noticeable when it failed.  But, if its small and has been there for a long time...

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