Evan70

The car was running fine Monday evening, but yesterday is lost 3psi of max boost. Runs fine at low boost levels, and runs ok at full throttle as well except that it isn't making full boost. My mechanic and I tentatively are thinking it's the custom test pipe I had done on the exhaust (piece of single wall pipe welded in place of the cat), and that the double wall section may have partially collapsed. Of course the only way to really verify this is pull of the exhaust and cut it open to check. Just wanted to get opinions on if this sounded like the likely cause before going that far. I can turn up the boost with my EBC, and the loss is pretty consistant no matter what I set it to (loosing the same 3psi no matter what level).

special tool

Watcha got for a wastegate, dude?

Porsche-O-Phile

That'd be something to check for sure. Any reason it might've collapsed? Either that or I'd check the connections around the wastegate, and all the silicone connections (intercooler, throttle body, etc.)

Evan70

LR dual port wastegate. I've pulled all the intake connections and couldn't find any leaks or blockages, so we're pretty sure it has to be on the exhaust side. The only thing I can really think of why it might have collapsed is that I heard a very quick metallic scrape going over a big bump last week. They thought they might have hooked the wastegate up backwards when they did the clutch, but we double checked it and it's correct, plus it was boosting fine right after the clutch change and didn't start this until the following day.

One other thing that I think relates to this. I've noticed over the last couple of months a "whooshing" when I let of the throttle when being hard on the boost. I've been through the intake track several times looking for a leak that would be causing this, and even replaced a couple of hoses that wheren't bad but had some small cracks in the outer surface appearing with no success in eliminating the sound. My thought now is that if the exhaust has been collapsing slowly over the last couple of months, that could have been causing extra backpressure that may caused the whooshing? Then if it had a major collapse yesterday, that caused the loss in boost. Sound reasonable? I guess it really just needs to have the exhaust pulled off and checked to see if that is in fact the issue.

special tool

How did your bypass valve test pan out?

Evan70

Haven't checked the bypass valve, it's only about 3 months old. Any easy way to test it? Just blow through it? I have checked the vacuum line running to it, and it's fine.

IanS

You can push it open and stick your finger on the vacuum nipple to seal it. If it stays open, its good. If it immediately shuts, its bad. A vacuum tester is better, and a finger isn't a perfect seal, but it should tell you whether its toast.

Evan70

Ok, I'll check it tonight. I'm also beginning to wonder if maybe the wastegate might not be going bad or having an issue. I say this because they did have to remove it to replace the clutch, so with this happening so soon after it might be related. Either that or they may have nicked one of the vacuum lines running to the wastegate.

Evan70

Ok, checked the bypass valve and it's fine. Verified vacuum on all the vacuum lines, although I didn't really think there were any issues there since vacuum reading at idle on my EBC gauge has remained consistant (and changes when even one line is left open). Verified the shop hooked the vacuum lines up correctly to the wastegate. Also checked the temp on the wastegate pipe while idleing, and it remained completely cool, so I'd guess the wastegate is fine as well. While under the car, I did notice a nice big dent (about 2-3" long) right down the center of the exhaust pipe before the new cat bypass pipe. So at this point, unless someone has any other ideas I guess I need to have a shop pull the exhaust off and check it.

Evan70

Only other thing I can think of to try, I do still have the Lindsey MBC in the car althought it's not connected. I guess I could hook it back up in place of the EBC and see if it makes any difference.

Evan70

Well, I finally found the issue. Stupid hose that used to go to the cycling valve from the J boot was leaking a little where I had it capped. Only found it after pulling everything apart and pressure testing each hose. Don't know why I didn't do it before, but this time I just plugged it right at the J boot itself.