Possible Turbo CBV fail? Need help diagnosing my 850 T5-R

kaj2003 · Post by **kaj2003** » 21 Feb 2012, 17:07

Recently I've noticed a dramatic reduction in fuel economy and completely sluggish performance. My turbo boost gage will show a boost just like normal. But I feel no torque surge and hear a lot of air hissing. If my compressor blow off valve has failed, I'm kind of confused as to how my boost gage still shows pressure. Am I correct in diagnosing this as a CBV problem?

*I checked all my hoses in a quick visual scan. Everything seems connected and in good condition. No check engine lights, etc.

Rfallon84 · Post by **Rfallon84** » 21 Feb 2012, 19:57

I myself am having a similar issue with a sudden power loss, sluggish start I hear the turbo hissing louder than normal no surge. It doesn't feel like its boosting, and the car won't accelerate after 4000 rpms. Do you have any similar symptoms?

Post by **jblackburn** » 22 Feb 2012, 07:04

Rfallon, AIR HOSES!!!

Kaj, it's possible for the turbo to still build some boost with a bad CBV, but it won't be the full 9-10 PSI it should (the gauge won't go over into the right if you floor it above 3500 RPM). I would also double check your air hoses for small holes - the one near the throttle body likes to blow where it connects into the idle control valve.

I've got the fluttering noise when you gas it and let off hard above 4000 RPM, and more hissing and less power than normal - both signs that the CBV diaphragm is torn on my car.

Rfallon84 · Post by **Rfallon84** » 22 Feb 2012, 16:29

Thanks jblackburn! I found a rip in my lower inter cooler hose, swapped it out with a new one today problem solved. All other hoses look great.

kaj2003 · Post by **kaj2003** » 03 Jun 2012, 11:36

Here's an update:

I found a couple of my hoses by the throttle body and down beside my air box. Sure enough, a couple of them were torn and disintegrating. So I replaced them. Right away, I had instant boost pressure build and it held thru the revs and fluttered when I let off the gas abruptly. It was more boost pressure than I've ever felt since I've owned my T5-R, which is about 3.5 years.

BUT...

A day later, everything went back to the way it was before. I rechecked my hoses, and they were all fine. So as it stands, I have no boost building , terrible fuel economy, no CEL, hoses are good, and it smells like it's running rich.

My theory is that once I fixed my vacuum leak from the hoses, the system went back to full boost. It hadn't run at full boost in a long while, so when it did, it exposed the weakness in some other part of the system. I'm back to square one. But I ordered the IPD CBV, and I'm going to put it in today. In the process, I'll check the hoses hidden down back there.