Even a new wastegate didn't solve it?? Strange...

If mechanical cause, for it to completely dump boost you're talking a large line coming loose. A small vacuum hose won't vent that much air. Disassemble and inspect the large rubber lines between the turbo outlet and TB (if you haven't done so already).

 

Ive now checked all hoses, pressure checked the intake multiple times. Ive also determined it is not dependent on a certain boost level as when I mess with the MBC it will do it at 10psi or 15psi. Its like when it reaches peak boost it dumps all boost. Problem is that I have no idea where it is dumping it from. I have a WG to atmosphere and I dont hear it dumping from the WG. I also dont hear the "whish" from the BOV.

I am at a complete loss and have no other ideas to try. FML

 

I have to think an exhaust leak large enough to lose all exhaust energy would probably be obvious (should be able to see a large crack or open flange). Same w/ an intake leak. Engine probably cannot run w/ a metered air leak large enough to lose all boost pressure. And I cant think of an internal turbocharger problem what would allow it to build boost but then quickly stall it.

Do you normally hear the waste gate opening over the rest of the exhaust noise (open exhaust - no muffler, right)? I have had my WG stick open, and I did not hear anything unusual over the exhaust (open pipe). But my WG bypass is tied in like a stock system, so it vents out the tail pipe, not directly to atmosphere.

Does the boost always dump around 4k, or anywhere its brought up to full boost? So would do it at 5k if you waited to hit full throttle until higher rpm? What about at 3/4 throttle? Normally some boost will build and hold at less than full throttle? Does it dump boost under partial load too?

And I don't mean to be patronizing/irritating - but to confirm, the MBC is routed from the intercooler pipe directly to the WG diaphragm, CV is bypassed (?) Did you try clamping the WG line or removing it from the diaphragm connection?

What type MBC, black **** pressure regulator or ball/spring (LBE type) pressure relief? I have had the ball get stuck in the pressure relief type a couple times - no boost. And not sure the pressure regulator type work well in single port mode.

 

Hey Jim

Yeah Im fairly certain it isnt an exhaust leak or intake leak. Ive checked my exhaust multiple times as well as pressurized the intake. Since I installed the WG to atmosphere, when it opens I can hear it since it is louder than my regular exhaust. I am using a muffler for the time being since I am testing boost around my neighborhood. Since I am not hearing the loudness of the WG to atmosphere I do not believe the wg is even opening.

It does always dump around 4k when on full throttle from the beginning. I havent tried slowly creeping it up however I am headed to a friends and will test it there.

You are correct that the MBC is in replacement of the CV, directly from the IC to the wastegate. I am using a black pressure **** style that I got at Grainger this morning.

I havent been this frustrated and at a loss with my car ever. The only thing I can think it could be is the turbo but I cant comprehend how that could be. I spoke to the guys at Lindsey and they agreed that it does not seem like a turbo issue.

The thing that is baffling me is I cant figure out where the pressure is going. The only outputs are the BOV and WG, assuming no leaks in the intake. Given that Ive replaced both I just dont know what to do next. I also cant figure out where its coming from based on listening because it does not make thee "whoosh" like the BOV does nor do you hear the loudness of the "open header" when the WG opens.

 

Could the BOV be opening slowly enough that you can't hear it, then sticking there for a little while? Would it be worth plugging the two BOV hoses and taking the car for a quick drive? As you said, the boost pressure MUST be going somewhere... and slowly since you can't hear it. And if your intake is stock, the BOV isn't going to be all that loud in the first place. I know... It seems like trying a new BOV would have already eliminated it as a potential cause, but where else can boost pressure go *quietly*?

 

Solved it. Will post details later. Very simple!

 

My breath is bated... I'm puzzled if it hasn't been already covered...

 

Do tell!!

 

Well after searching and searching I had Omni serve as a fresh set of eyes on the car. HE took it out and saw that at various RPM's of boost it would cut out and go to vaccum. This lead him to believe it was a colapse of some sort in the intake. Since I had remove the OEM box and used a cone filter we thought maybe the filter had colapsed. After checking we found that the replacement hose I had used to the inlet side of the turbo was very weak and must have been colapsing when under boost. This cut off the flow of air to the turbo. We ended upi putting in the stock box unit and back came my boost.

Goes to show that messing with original designs isnt always a good idea. Im very happy we found the problem and it didnt cost me any track time.

Onward and upward to Road America tomorrow to hopefully have a good showing in G class. Thanks to everyone for the help and a BIG THANKS to Jim (aka Omni) for finally figuring out the issue after I had weeded out everything else.

Brian

 

glad you got it fixed... and yeah there is alot to be said for leaving them alone! Course I won't either but still....

 

Glad we got it working. This is a great example of how friggin' HARD it can be to diagnose something over the internet! I was right there with oddjob - based on your descriptions I was certain it was an electronics issue. His "offensive" comment (LOL!) about double-checking the MBC routing was exactly the same thoughts I had and was one of the first things I asked about when you brought the car over.

However, all it took was a short drive around the block, experiencing it for myself, to figure it out. The motor literally choked and I could get it to do it at various RPM levels... it was definitely FLOW related. 4500rpm and 12psi in 2nd gear, or 3500rpm and 20psi (oops... MBC set a little high!) in 3rd. The dead giveaway was the boost gauge showing 5-6 inHg *vacuum* at WOT when it was acting up.

Surprised the neighbors didn't call the cops for our repeated 3rd gear blasts down the street....

 

Good find, Jim! This is one of the reasons I'm a fan of OEM parts...even though I deviate enough to not be a purist.

 

Great that the car is running so Brian won't miss the RA Club Race.

Agree, often hard to help diagnose problems w/o seeing firsthand, so end up w/ not much more than a guess. But I have taken advantage of others' insight here, so try to throw out some ideas when someone is looking for troubleshooting tips - even though I occasionally get a response like this...

 

I would be interested in seeing the actual hose that was colapsing. What type were you using? I have a flexible hose off my MAF that runs through the fender and into the nose behind my fog light where the filter is. I used 3" silicone brake cooling hose. No issues at my last track event, but you have me thinking...

 

Wow if I got a response like that to my efforts to help someone I don't think I'd ever offer support to the boards again!