Well I always thought that the brand new BOSCH diverter valve was not the culprit for the lack of achieving boost. DUH better to check than guess! Blocked off diverter valve by shoving a 1/2" pipe plug into the hose and presto!!! BOOST! Scheisse wish I would have checked that a long time ago. FYI getting an aftermarket one now. Looking at TurboSmart and FORGE.

Thanks
Mike G.

 

Lots of fake ones out there...

 

I bought a legit one a few mins ago. It's machined from only the finest material available and I got it gold plated to match my Daytona Rolex watch. NOT!!

Mike G.

 

I have 2 Forge, 1 black, 1 silver $55 each shipped in US

 

Bummer! Too late already ordered one.

Thanks
Mike G.

 

Since the diverter valve on the '89 Turbo was last changed 20+ years ago, I ordered an APR R1 since I've had one on my modified A4 1.8T for 11 years with zero issues.

 

I thought about getting that one too but ended up with one from Evolution Motorsports.

Mike G.

 

Just be careful of orientation. My Turbosmart needs to be fitted backwards compared to stock unit. I triple checked on turbosmart site with mine to confirm, so make sure you check makers site

 

Yeah same for the Evolution Motorsports one. But get this, the guy said it will operate both ways but it will be much louder orientated in the stock like way. He recommended the "backwards" installation.

Mike G.

 

What is the "diverter valve"? I've been wrenching on my '86 turbo but don't recall anything, other than in the a/c system being called that.

 

See item 24 in this image (for late model turbo, '86 is similar) . The diverter valve, aka "shut-off valve" opens when you lift your foot off the gas. When the valve opens some of the compressed air from the turbine exit is bypassed into the turbine inlet to keep the turbine spinning between shifts. If the diverter valve is bad it can bypass air all the time and severely limit the amount of boost you can obtain.

 

Oh, ok. I'm use to having it called a "blow off valve". Thanks

 

Good explanation here too.

Blowoff vs diverter

Mike G.

 

Installed new Evolution Motorsports BOV . There was an improvement but still can not reach 15ish psi on the stock gauge regardless of gear. FYI: The part is a very nicely made piece.

Mike G.

 

Ok one more giant DUH!! Check all vacuum lines that go to the diverter valve. Dang mang the one that feeds to the top of the diverter had fallen off somewhere under the manifold. ALL IS GOOD IN BOOST land again. And wholly cow does a solid 2 BAR (Absolute ) boost make a difference.

Mike G.