Friday, January 11, 2008

Forge Diverter Valve Installation and Oberservations

I just purchased a Forge diverter valve, also known as a bypass valve, for my SAAB 9-5 as a birthday present to myself. My stock Bosh DV was obviously weakened, but the diaphragm had not deteriorated to the point of hooting. I ordered the FMCL007P Forge DV and spring set from for $135 plus $13 S&H.

I was surprised by how big it was compared to the stock Bosh DV. The extra bulk is mainly in the screw-off top. I installed the green spring and inserted none of the spacers.

Forge lists the springs as:

Green - 5-15 PSI
Yellow - 15-23 PSI
Blue - 23-30 PSI

Spacers are used to nudge the spring tension. The LPT 9-5 would use green or green with spacers. I would encourage people to try both the green, green with spacers and yellow springs and see what they discover for themselves. I have read of Aero owners using the yellow spring with spacers.I have no input to give about the blue spring because I don't want to try it out in my SAAB. I know it is too strong for my LTP and I don't want to damage anything.


This wasn't even a five minute job. Opening the hood took longer than this installation. I used a pair of pliers to release the two tension collars that hold the stock bypass valve in place. The valve comes out with some wiggling. Carefully remove the vacuum hose on top with your fingers or with a very light touch of the pliers if it is stuck.

Then install the new Forge bypass valve by reversing the steps. I guess you might leave the vacuum hose for last when you install. Some people post about the vacuum hose being too tight to go on the new diverter valve. The advice given to them is to heat the little hose in a glass of hot water to make it more pliable. I didn't have any problems installing the vacuum hose on mine.

You can see how much more it sticks out compared to the Bosh bypass valve. Plenty of clearance on the 9-5, so this isn't an issue.


My stock diaphragm style Bosh DV was weakening and didn't consistently hold or release pressure. The Forge DV has increase the feeling of performance, but obviously just replacing the failing DV has made a difference. I leave it at this because don't have a turbo pressure gauge or dyno to confirm my feelings with hard numbers. The T7 recognizes when the turbo pressure is too great and responds by lowering performance, and I have no idea if there is a gray area of increased turbo pressure; where there is more boost than stock, but not so much that the computer fights it. One SAABCentral poster described a 1-2psi increase after adding the Forge with a yellow spring. The pressure being read from his after market gauge. But like I said, I don't have any instruments to read the pressure or performance and the SAAB 9-5 likes to foil bolt-on performance parts.

There is also a difference in sound. The Forge has what I would call a three syllable sound. My Bosh only had two syllables when it released. The Bosh was a K-Shhh sound and the Forge is more of a K-tik-Shh sound. It doesn't sound is any louder, it is more that it now sounds like a "BOV" instead of a random air leak; same volume, more distinct sound.

More information about Forge and Bosh diverter valves.

"The great diverter valve face-off"

The SAAB 9-5 uses a diverter valve (DV) or bypass valve in place of a blow off valve (BOV). The casual term "hooter valve" is sometimes used because of the sound it makes. The DV functions like a BOV, but it recirculates the released air back into the air intake instead of releasing it into the atmosphere. I haven't tried it, but I understand that letting the SAAB 9-5 release pressure into the air will be read by the T7 as a vacuum leak and the car will go into limp mode with a CEL.


Getting a performance diverted valve, like the one made by Forge, and installing it in the reverse configuration will further enhance the sound of the turbo.


  1. Nice how-to there. My stock DV also gave up on me a few days ago, so I ordered a new one from genuinesaab. Being a complete newbie to turbocharged engines, I used your guide to install my Forge DV. However, I have one question I'd like to ask you. I also received two springs and two "coins" along with my DV, but I have no clue as to what I'm supposed to do with them. Could you please do a quick write-up on how/where to install the springs (and "coin"/spacer)???

  2. Thank you for your comment, I will be happy to.

    The Forge DV comes with the green spring installed, that is the softest spring rated for 5-15 PSI. You can open the DV by twisting the top of it open like a jar. This is how you switch springs or clean the DV. The two extra springs are used to tune the DV for various cars/turbos. I encourage you to try running the car with the yellow spring some time and see what you think.

    The spacers can be placed on top of the springs inside the DV to make them slightly stiffer if you find that the next larger spring would be too stiff. After you try the yellow spring, if you find it too aggressive, I would encourage you to try the green spring with one or two spacers.

    This is not to say that the green spring with no spacers isn't right for your SAAB, but it only takes a minute to switch the springs when the DV is installed (just remove the vacuum line and twist off the top), you might as well experiment to find what works for you.

    There is also a blue spring that came with in the box. I wouldn't recommend using it because the tension is too much for a stock SAAB and could damage the turbo.

    I hope this helps you out. I will update the post with photos to show how the DV opens and what is inside. I'm not sure why I didn't think to do that when I was taking photos yesterday.


  3. Thanks for the quick reply. I haven't tested out the spring load/rate yet, but at least I now understand where to put the springs and spacers. BTW, I really like your blog and enjoy reading each new entry, even if it doesn't necessarily apply to my Saab (yet.) We really need more folks like you to educate the new guys about Saabs (they're not like Honda Civics...and I'm glad they aren't.) Keep up the good work!

  4. You're making me blush; thank you for the kind words. I really enjoy the whole process... from working on the car, taking photos, and making posts. I'm glad that I was able to help.

  5. I have a Saab 9-3, and I want to replace the diverter valve with a Forge. I can't locate the stack divereter valve. I have seen some blogs that say the the valve is located just under the are where the intake tube mets the turbo, but I can't find it! Does any body have a pictur prompt reply.e of where the valvre is located? Thanks for your prompt reply.

  6. Here is a photo from my 9-5 showing where the DV is located. I think the 2.0 has the DV in the same place. You can see it at the center right of the image. It's black with an aluminum tube sticking out of the left side.

    I'm far from an expert with the 9-3, but I did find a forum thread at SAABCentral that has some images that might also help you. Good luck!


  8. It's my understanding that the 9-5 ECU is located between the windshield wipers under the black plastic panel between the engine bay and windshield. I don't know if this is the same location for the 9-3.

    So it will basically be under the black/faded gray panel in the center of this photo.

    I've never taken the panel off myself, so I can't give you any real specifics.

  9. Do you have the DV in your car in reverse all the time? how does it work like that, is it safe?
    Thanks, Sebastian

  10. @aerokid923

    That's correct, I'm running my DV in reverse all the time. It shouldn't hurt anything as long as the spring is strong enough to hold the pressure. The stock "diaphragm" style DV or a weak spring would open up and reduce peak turbo pressure if it was placed in reverse because the pressure is now pushing directly against the plunger/diaphragm.

    If the pressure was to open the DV prematurely, nothing would be hurt except for vehicle performance.

    Keep in mind that this is not a chance to use a stiffer spring than required. Too stiff a spring will cause the T7 to cut power as a way of reducing the extra boost pressures, but this warning applies regardless of which direction the Forge DV is installed.

    Good luck, try both directions and see which configuration you prefer.

  11. Is the swapping or type of DV any different for the 3.0t?

  12. Good question. I had to look up the answer. The DV part numbers are the same for the two engines, so I'd say the DV itself is 100% compatible and the installation process should be similar. But I'm not finding a clear photo of the V6 to see how and where the DV is installed and I have no hands-on experience with the V6.

  13. I have a 02 9-5 aero (auto) and replaced the bov with the forge kit. Using the green springs, the car seems weaker than stock. Using yellow springs, the car is a monster, but the cel comes on. Next I am going to try the green with two shims and see what happens.

  14. I bet you'll be happy with the two shimmed green spring.
    Your Aero gets higher pressure than my base 9-5, I'm kind of surprised yellow gave you a CEL. I've ran with the yellow spring and, while the car didn't like it, it sure didn't trip the CEL. I've done green and one shim in mine, but I currently have the green spring installed with no shims.
    Fiddle with the configuration and springs, test and see what happens, have fun!

  15. Hi I just picked up a 2001 Saab 9-5 Wagon 2.3T4 which I love. I had the engine light come on and checked for a code P1110. Sounds like the diverter valve although it runs OK. I'd like to swap in the same valve you've used. Will this part number (FMCL007P Forge DV) work with my vehicle and would you think the stock green spring OK?


  16. Also what does revers configuration give you over regular stock position? Better performance, different Turbo sound, both?


  17. Yep, the 007 will work and you'll want to go with the green spring.

  18. There's no performance change, but it'll give a crisper sound when the DV opens.

  19. I have a question. Do you know what the symptoms of a blow diverter valve?

    I suspect mine is dead, it does the following things:
    -When the turbo gauge hits the orange section and remains in that area, there's a medium-slight hiss coming from the hood. If I give it more gas it'll stop hissing and the boost feels pretty decent as it goes to red.
    -When I let go of the gas (it's a stick) and coast keeping it in gear, it will start humming and the car will slow down slightly faster than it should for a given gear. It's pretty slight though.

    I checked around the hood for any obvious breaks in vacuum lines or any sign of problem somewhere else.

    Car drives ok, maybe a bit less powerful than it should. One day, driing pretty hard around town (DC) the check engine light came on, so I got a reader and it found code P1181 which is "Long term fuel trim additive. Max Value, Air/Fuel too Lean". Cleared the code and never got it again.

    I just took out the DP, checked the turbo and replaced the exhaust with one from Custom Tubes (2.5").

  20. I think of a bad diverter valve as being more of a honking noise. Have you checked out the waste gate on the turbo? It might also be that and I don't want to send you out to get a new DV only to find the problem is elsewhere. If everything on the waste gate seems okay, then I'd go ahead and replace the DV. Hey, look at the bright side, it could be an opportunity to upgrade to a Forge DV!

  21. Thanks for the hint, I didn't think of looking at that. Too bad I didn't do it when I had the whole exhaust off. I might order the Forge DV regardless since my DV is 9 years old and probably on the way out.

  22. I got my Forge DV today but am still waiting for a silicone vacuum line to come by mail as mine is getting a bit powdery and old.

    While looking at the wastegate, I didn't find anything really wrong, but I did find that one of the main silicone vacuum lines next to it (there are 3), which goes to the passenger side of the engine bay and towards the cabin, has what looks likes two tears. However, I have no idea what that vacuum line does (as it is not tied to the wastegate but goes somewhere unknown).

    I'm probably going to install the DV and then bring the car to a mechanic to change that damaged vacuum line, which will hopefully clear the P1181 code I keep getting (more frequent now). However, if you know what that line does, I'd appreciate any insights.

  23. Try taking a look at the images in this thread and see if they are any help.

  24. What if I were to reverse the Bosch one in reverse that is already in the car

  25. Sadly it's not strong enough to hold back the pressure and you'll see less performance.

  26. Just purchased a 2005 Saab 9-3 ARC and was wondering if my car has this diverter/bypass valve? Could not find anything but haven't had the car that long. Thx

  27. Yep, your 9-3 ARC has the same DV as the 9-5. This Forge DV (and other brands that fit the 9-5 or the Volvo S80 turbo) will fit your '05 ARC. Congratulations on the new car.

  28. Hoping I might be able to get a timely response on this thread, anyhow I recently purchased a 2003 saab 9-5 5 speed 2.3t I removed the stock air box and added a K&N air filter to it which made the turbo sound much better spooling up, I came across this thread and found that this was the next thing I wanted to do, I found a brand new turboXS diverter valve on Craigslist the box had no instructions the spring in the valve is supposed to be the stock one I ran it yesterday no issues start my car today check engine light comes on not sure if my hose has a leak (is pretty dry rotted) or not my diverter valve is getting warm after using please she'd me some light

  29. Hello! I'm still lurking around the site. I'm not familiar with the TurboXS DV, but you'll want to start by getting the error code checked with a scan tool to help point you in the right direction. Regardless of what the ODB-II code tells you, it sounds like it's time for new vacuum lines. Buying about two yards worth of silicone vacuum line gets you enough hose to replace all of the original pieces on the car. Even if it isn't the cause of your error code, it will at least save you from vacuum leaks in the future. Good luck! Hopefully it's something simple.

  30. Thank you for your timely response, I plan on getting new lines today. Is it common for the diverter valve to get warm/hot?

  31. I recall it being hot enough after driving the car that I didn't want to remove the DV with my bare hands, but I don't recall mine getting any hotter than the surrounding metal parts under the hood. That doesn't mean it didn't... I just never noticed if it did. My guess is that the heat is normal. The air is coming right out of the turbo. But I don't want to give you a definite answer in case it really is a symptom of something wrong.
    It would be a good question to ask on one of the SAAB message boards. Maybe even talk one of the members to run outside to their car to see how hot their DV is getting. I'd check for ya, but I don't own the 9-5 anymore.

  32. Okay thanks for your knowledge thinking about getting a scan tool off of eBay will post the outcome