BOV lets off when cruising in vacuum???

[Turbogsxmitsu]

Ok, Ive had this problem for a while, just want some opinions. When i drive my car easy, at low rpms, while in vacuum or low boost (1-5 psi) my BOV which is a type S Greddy opens relieving any pressure and starts spuddering like its opening and closing real fast over and over. What the hell is going on??? Let me know whar you guys think. I took it apart and made sure everything looks ok and still it does this. It makes it real hard to daily drive her. O yea it does not do this under heavy acceleration. thanks

 

[romeen]

It sounds like there isn't enough spring pressure holding it closed. Under heavy acceleration the higher boost pressure in the BOV vacuum line helps to hold the valve closed. In low vacuum (easy cruising) the spring pressure apparently is not enough to keep the valve closed against the vacuum trying to pull it open. If it is supposed to have an adjustment screw make sure it didn't fall out.

 

[delta448]

^^I agree.
Is your boost gauge connected to the intake mani? Seems a little unusual that you're actually seeing positive numbers on the gauge and the BOV is opening.

 

[Turbogsxmitsu]

The bov adjustment skrew is almost all the way in. Its so weird, under heavy acceleration its perfect, but while cruising it lets off. WTF! IT makes for horrible cruising.

 

[danny_l_2005]

I think you problem is that your turbo is getting compressor surge at low boost because your adjustment screw is very tight making it hard to open the bov at low boost making it surge. I had the same problem with the bov at the softest setting, what I did, I converted it to a single spring. Now it works great. Remember the adjustment screw's purpose is to make the bov open at a certain vacuum, and was not meant to adjust it for hold more boost.

 

[romeen]

Pressurize your intake (boost leak test) to see if the valve is holding pressure. If you don't have the equipment to do this you can remove the BOV and push against the piston (or diaphragm--I'm not sure how the Greddy is designed). On my BOV the piston is quite stiff--- it takes both thumbs and quite a bit of pressure to push it open. And that is with it adjusted to the minimum amount of spring tension needed to hold boost (so I minimize any chance of compressor surge). If all else fails you can consider using a longer set screw to pre-load the spring more or a stiffer spring. If you do this use care and increase tension gradually to avoid compressor surge. Good luck.

Edit: Just read your post danny l 2005, yes this would be something to consider as well.

 

[Turbogsxmitsu]

If I loosen the adjustment screw it gets worse!

 

[romeen]

You can try a longer adjustment screw as I mentioned above. If you do this, measure the depth of the screwed in portion of the existing one. Use that as a guage to determine how far in to start the new longer one and make adjustments from there.

Also, danny l 2005 said something about converting his to a single spring to decrease tension. Again, I'm not familiar with the Greddy design but if it is supposed to have two springs providing tension and you only have one then that may be your problem. Just a thought.

 

[kmoore]

Is you BOV's diaphram sealed correctly? What I mean by that is, if you take off the BOV completely from the car and look at the bottom where the diaphram meets with the base of the BOV, is it tight up against the bottom so that no air can leak through?

 

[danny_l_2005]

You can try a longer adjustment screw as I mentioned above. If you do this, measure the depth of the screwed in portion of the existing one. Use that as a guage to determine how far in to start the new longer one and make adjustments from there.

Also, danny l 2005 said something about converting his to a single spring to decrease tension. Again, I'm not familiar with the Greddy design but if it is supposed to have two springs providing tension and you only have one then that may be your problem. Just a thought.

Apparently our cars like the adjustment screw to the softest setting, so does the evos too. Here's a link for you which can help you do this single spring mod. http://www.evomoto.com/tech_info.php?tPath=1&tech_id=7 Also, as kmoore said, check the diaphram if its sealed correctly. Any vacuum leaks in the diaphram can make the bov harder to open and causing compressor surge