Contradictory Blow off Valve

[gallacmic]

I have a vent to atmosphere style blow off valve with the two barbs on it. The 1st barb is on the top portion of the blow off valve and the 2nd plums underneath the diaphragm. The 1st barb on top has a hose that recieves both boost and vacuum as it is plumbed to the intake manifold. The 2nd barb is plumed to the pipe that the blow off valve is mounted to so it only receives boost pressure. The problem I am having is the screw is adjusted all the way out to try and get rid of the compressor surge which is evident by the loud psh psh psh psh sound I get when I shift instead of the one loud smooth PPSSSSSSSSHHHH! But the stupid thing is with it adjusted all the way out it is getting compressor surge but it wont let me get full boost (9psi). If I tighten the blow off valve screw I can get my full 9 pounds and it always surges. If I loosen it it surges and I lose boost. WTF!?!?!?!?!?!?
If its adjusted softer to where I'm losing boost pressure why in the world am I still getting compressor surge???

[vanilla gorilla]

First off what kind of car do you have? 2nd what blow off valve are you running?

[gallacmic]

Its a 98 2g Eclipse with a 420a turbo.
Here is a link of the exact same blow off valve
http://www.ebay.com/itm/UNIVERSAL-AD...item2eb8e1be72

[david-b]

Cap the lower barb. All you need it one vac/boost port on the BOV. Get rid of the second lower hose, and cap it off. The top connection will see (as you stated) both vac and boost, which will open or close the BOV. With the lower one connected, it's pushing the diagram open while the top is trying to do the opposite.

[gallacmic]

Ok I will definitely try that but that makes no sense why they would make a blow off valve that fights itself like that. To my understanding the lower and upper barbs deliver in my case 9 psi above and below the diaphragm which is an equal amount of pressure therefor cancelling each other out as far as moving the valve open or shut. The spring on the other hand is in the upper portion holding the valve shut and when the throttle plate slams shut it now has 18 psi vac pressure in the top portion and 9 psi boost in the lower barb and 9 psi boost below the valve itself in the inter-cooler piping. The idea is that should make the valve open rather quickly. But with how shit goes on this it might actually do the trick to cap off that damn hose.

[SilvrEclipse]

Yes you are correct, the lower barb is suppose to be hooked up to boost only and is suppose to equalize pressure in the BOV. So the BOV only seals with spring pressure which makes for a quicker release. Most of us do not run the BOV setup like this, however i have never seen an issues come from using this setup. Also another things is that this is an ebay knock off BOV. I am actually using an ebay BOV and it works fine, had to replace the diaphram in it but doesn't leak. Like Dave said remove the lower line and cap it on the intercooler pipe, dont cap the port on the BOV.

[gallacmic]

K I will try that for sure. One thing I think might be a problem too is that the blow off valve shares the same "T" as my FMU. Not sure if that would be a problem since the air only pushes on the diaphragm in the fmu and the air does not actually leek out or anything. But perhaps I need to drill a hole and tap it so the BOV has an isolated vacuum/boost reference. What do you think?

[david-b]

Shouldn't matter. Manifold pressure is manifold pressure. Ideally you want each item using vac to have it's own reference line and use basically no tees, however here it doesn't matter.

[gallacmic]

Ok today I received my little air filter in the mail I'm going to use on the BOV just to make sure during idle it does not suck air in un-filtered. I also decided to do a boost leak test again just for kicks and found out that the 60mm throttle body has a major leek on the shaft where the tension spring is. Would a boost leek cause the BOV to not operate correctly? I know that under load and right when I shift my vacuum gauge reads 21-22 of vacuum that normally would go straight to the BOV to open that son bitch. I pressurized the intake to 10 psi doing the boost leek and the throttle body was hissing pretty loud so during 21psi vacuum would be twice as bad I think. Perhaps this is the culprit for my annoying BOV problems!! A STUPID O RING!!!!!

[SilvrEclipse]

Vac is no measured in psi, its 21 inches Hg. That shouldn't be causing the BOV issues you are having. If the leak was bad enough it would cause a high idle.