I just wanted to put this out there, in case it helps someone diagnose an issue in the future. I had an issue on my sos s/c'd s2k that happened essentially out of nowhere. One drive, everything was fine, the next drive, in boost my car just hit a brick wall, felt slower than stock, and would lurch if I tried to rev it much over 5k. Zero trouble codes, part-throttle driving / idle / cranking / etc. was spot on. Datalogging showed no vacuum/map issues, boost numbers looked as expected for RPMs where I could get the car to run.

One of the first things I did was pull the diverter valve, as they're known for having issues. I went through all the test procedures I could find online, blowing in, out, compressing the spring with an 8mm socket, holding my finger on the vacuum port, releasing, and even pumping it up with an air pump, then releasing the pressure immediately. It totally checked out, the valve would open as expected, and snap shut when pressure dropped.

Then I went about checking 2394823 other things on the car, all fittings, belt tension, shaft play, plugs, cat (in case of backpressure), hondata tune/maps, etc etc, none of which checked out. My next step was going to be to build a DIY boost leak tester, but I managed to find a new Bosch valve same day for cheap, so I ordered it. I swapped it in, first few pulls had a bit of stumble (presumably due to rich/partially fouled plugs), and after that she's 100% back to normal and running absolutely perfect again.

The best I can figure is that the spring finally just gave up the ghost, causing it to "leak" boost over maybe 4-5 psi. Again, I just wanted to put a word of warning out there for folks, in case anyone experiences the same issue and also tests out their valve to _seem_ in good working order.

Happy boosting!

 

Shouldn't the diverter be installed such that boost is applied to the skirt of the piston instead of the face, so it can't force the valve open?

 

Mine is/was fitted exactly the same way as the one pictured in this thread:
https://www.s2ki.com/s2000/topic/983...-strange-noise

Such that the boost is applied directly here:
http://imgur.com/rNnRwwP

In theory it can't force the valve open, if the spring behind the piston is strong enough.

 

To add some more insight, the diverter valve used in the Kraftwerks kits is a Bosch OEM unit used in several GM vehicles. I believe the SOS / Vortech / Comptech kits use the same or a very similar part. Here is how they are oriented on the Audi 1.8L turbo motor, as an example:




Notice the piston face is toward the air inlet, and the piston skirt is exposed to boost.

 

ha i just replaced mine with an all aluminum vf valve no more boost loss kept thinking my belt was slipping it serves as a second bov in my system after my godzilla bov failed 300 miles from home i added the deverter to the airpump inlet and it helped throttle response things are much better now