Bov not open at idle, spring too strong?

[invain]

We've been having problems with the car stalling out on decelleration and have tried a few different fixes. We took off and cleaned the throttle body, the iacv, checked for vacuum leaks, cleaned the maf, and we're still having the same problem. I noticed the other day that the bov (perrin) is not open at idle. My boost gauge shows -15 vac at idle, I know that's a little low but it shouldn't be enough to let the bov close completely. Is there any way the spring could be too strong? I have a garrett t3/t04e but am only running 7 psi. I know the bov works because I've watched it when my dad revs the car up, but I don't think it's working completely like it should. When it does open it's just barely, and sometimes it doesn't even go off at all if there's not enough pressure.

[DevilMB3017]

Also, if you're running a MAF sensor you also have to recirculate that air. That will cause your decel stall problem.

[invain]

Yeah somebody else just told me that.

Maf or not, the bov should be open at idle though, right?

[GTR PrYdE]

the bov should be open at idle though, right?

What?! No it should be closed until you make 1< psi, then when you let off it will open.

Revving at from a stop/no load, the bov should not open much, or at all. You stay in vacuum so there's no need for it to vent boost.

Hope this helps.

[neverlift]

is it adjustable? tried it?

I like my apg its adjustable cost like 6 bux and was decent for suck through ota.. even better on blow through

IMHO you should have lil venting at idle, when you lift sharply vac tends to be higher. As in way darn higher then the 15 you have

Also, YES that low of vac could have something to do with it.... solid vac is 18~22. I get 17 warm with 75 dollar piston/rings...

another thing, where is the vac sorce coming from? intake manifold is the place

[DevilMB3017]

Okay. Quick lesson time.

A BOV is in place to prevent compressor surge. This is what that means. You are driving down a street, boosting. You come towards a redlight and let go of the gas pedal. The throttle body closes, and this causes the air from the turbo to build up pressure, and because the turbo doesn't just stop spinning, it will still build.

Now this air has to go somewhere. A blow-off valve is a valve that 'blows off' this extra air. If not for a BOV you get compressor surge, which is the return of this air back into the compressor - in the OPPOSITE direction, which can wear a turbo or break it VERY VERY quickly. Some turbos are more sensitive then others, but why chance it?

To do this the BOV uses a vacuum source. When it has vacuum, it stays shut, allowing air to go into the throttle body - and into your engine. When it no longer sees that reference vacuum from an intake source it knows your no longer on the gas pedal and it opens to allow the air out - because this is at a higher pressure then the vacuum, so the BOV knows whether to open or closed.

Now, some BOVs, specifically the HKS SSQV uses a diaphram in this sense with no adjustment.

Some BOVs, like yours, have a spring in it for partial throttle applications. When your boosting a little bit, and only on partial throttle, you are close to even on the vaccum and the boost. This would make the BOV start to open, even though that air is supposed to be going INTO your engine, it is going out the BOV. This will cause problems, so you use the spring to adjust how much boost/vacuum ratio it needs to open.

Finally....

With a MAF on a draw through setup, which is where it is on your turbo, it meters the air, then it combines with the turbo and goes into your throttle body. The ECU uses this and the O2 sensor to determine fuel required to burn. When the BOV goes off, the ECU thinks this air is going into your engine, which is why you need to recirculate it AFTER the MAF, but before the throttle body. The close to the throttle body the better iirc. With a 'blow-through' MAF setup, you can place the MAF on the cold side of your intercooler, right before the throttle body, and this would allow you to vent the BOV to the atomsphere because the ECU will never know that air was there. This is a little more complicated in tuning, according to some people.

Hope that helps and gets added to a "noobs read" thread...I'm looking at your abc123omg

[480sx]

Takes a lot of compressor surge to ruin a turbo if were talking moderate levels of boost. At high levels, the damage o/c will take less time, but even then its not something thats going to happen instantly. If your boosting past 25-30 psi, a serious case of compressor surge can actually shatter the compressor wheel.

Two things happens over time and consistent compressor surge. Your turbine shaft is forced against the walls of the bearings, accelerating bearing wear. Your turbine shaft will also warp, which causes all kinds of problems.

At low boost levels, compressor surge does little to nothing to a turbos life.

[neverlift]

just look at nissan factory cars(US) and most had no bov. Its not needed with low boost as said, but it makes the cool noise we all love will it make your turbo last longer? cant honestly say due to SO MANY variables...

but this isnt a to use or not to use post...

if this is a piston and spring setup add some wd40 or graphite something to the piston walls, my ebay stuck after sitting for like 3 months

[invain]

I haven't lubed it with wd40 or anything but it was stuck open when we first got the car. Somehow it opened up too car and the piston cocked inside and jammed.

I'm probably going to look into getting a different bov now though.

[neverlift]

find a volvo with turbo and get an agp, adjustable and has a pretty nice sound IMHO but still find out why yours isnt working, IIRC perrin is decent stuff

[invain]

I'm almost wondering if setup for vacuum to the bov right now isn't the greatest. The line from the bov goes up to a 3 way connector with 2 more lines coming off it, the line supplying that splitter goes to another 3 way splitter, and from there I don't remember.

[neverlift]

I'll cut your *** serious though man try running it just off the fpr line T into it from the back of the intake manifold.... IMHO you should only T any line once.

[invain]

Yeah I really gotta find somewhere different to get vac for the bov. I know it works, but the vac is so low it's not working 100% like it should be.

[esahuque]

If your vac is that low, you need to make a boost leak tester and test for boost and vac leaks. there is a post about making a boost leak tester somewheres on here, just search.

[240sxvaj]

First things first, check for vac leak and then get a compression check. replace that bov w/ something like HKS ssqv. ssqv is one of the best working bov out there, but it is really up to you on what brand you like. anything that will help make something last longer is always a +, better safe than sorry.

Also, run blow thru if you dont want the car to stall while decel, or recirculate that bov.

[invain]

I'm probably eventually going to get a different bov. We have checked for vac leaks and found nothing.

We've also done a compression test, and the first cylinder rings are pretty worn. Compression was real low cold, but gets better once things are warmed up and expand. I already plan on rebuilding the engine next spring, I just have to get by with the way it is untill then.

[neverlift]

ebay pistons are only 75 bux with rings/pins shipped! holding up pretty good, even with me drifting @ 225* collant temps....7psi daily

[invain]

I leave for college in 3 weeks and this is my only car. With work and other stuff a rebuild just isn't possible right now. My dad is a certified mechanic so the labor is no problem, we just don't have the time right now. Once I'm at school I'll barely ever drive the car so I'm not too worried about it for the winter.

[240sxvaj]

since it's your daily then i recommend having an extra motor on the side incase something goes wrong, or you can build up the extra motor slowly.

[invain]

I have absolutely no room right now to recirculate the bov before the turbo, my air filter is literally almost touching the front support. Is there anywhere else I can send it instead of before the turbo?

[240sxvaj]

I have absolutely no room right now to recirculate the bov before the turbo, my air filter is literally almost touching the front support. Is there anywhere else I can send it instead of before the turbo?

I dont think there's another way to do it, but to put it right before the turbo. also you should have room since the maf is suppose to be around 12" away from turbo or else it wouldnt idle and drive good. you should take a picture of your engine bay because i dont get how you dont have room to recirculate on turbo intake pipe.

Other than that just go blow thru.

[invain]

My maf is right after the turbo, lol. That's why I don't have room. I do plan on moving some stuff around eventually, but for now that's how it'll have to be. I've also read that having the maf close to the turbo may not actually matter much, some people have different opinions on that. 12" or 1" from the turbo, the same amount of air is still going through it.

[kouki_hmongster]

wow so many people even me had problem w/ maf being too close and you are not having any problems? maybe the maf being too close is the problem. hows the idle? you should try moving it a little further and see if it helps, but still i know it will die on decel. you can just leave it in gear while coming to a stop and it wont stall. thats how my bro use to do it.

[invain]

It's definitely gotten better, I can drive it around, even in a busy city, without stalling it out. I can throw it in neutral now from 5th gear and coast right up to a stop sign, I just have to be ready with the throttle just a teeny bit.

I'm curious though, why exactly does everybody say not to have the maf close to the turbo. I just don't understand how that could possible have any effect, even if it was 4 feet away the same amount of air is still gonna flow through it.

Maybe I'm an idiot and the maf being close is my problem though, how would I go about testing for that? Should I remove the maf and see how it idles, etc?

[480sx]

The turbo creates a vortex that tricks the MAF into thinking that there is more air flowing through it than there really is. Causes all kinds of drivability issues.

[neverlift]

IMHO suck thruough sux blow through is way better in terms of performance/functionChances are, even with a fully adjustable bov if your not recirc then your more likely to have stall issues, sure blow through could hav eissues if you a tard and put the bov after the maf... IDEAL IMHO is this :turbo inlet<intake pipe<filterturbo outlet>hotside>IC>bov>maf>throttle body

My setup started out suck, wasted gas and safety made my switch to blow thru( having you brake foot on the gas to not stall isnt smart .02