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99 s turbo
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97 Posts
Discussion Starter · #1 ·
hi all, today i took off my recirc pipe from the wrx dump valve, i blocked the recirc pipe and took it for a blast to hear the noise, it does actually work BUT....... when i come to a halt the engine idles at about 200 revs and wants to cut out, so i took it straight back and put it back on, my question is, would a bov have the same effect of what happened when taking the recirc pipe off, or would the car run idle at higher revs, thanks
 

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Official sf.org decal guy
2006 FXT
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12,366 Posts
hi all, today i took off my recirc pipe from the wrx dump valve, i blocked the recirc pipe and took it for a blast to hear the noise, it does actually work BUT....... when i come to a halt the engine idles at about 200 revs and wants to cut out, so i took it straight back and put it back on, my question is, would a bov have the same effect of what happened when taking the recirc pipe off, or would the car run idle at higher revs, thanks

Hmm not sure why it would have acted like that at idle (assuming the recirc hose was sealed). The only time I would expect the car to perform differently is when you closed the throttle under boost that the BOV opened, dumping metered air to atmosphere. Then you would likely get some stumbling.
 

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2004 Forester XT '06 STi 6MT
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707 Posts
your recirc valve is a bov. it's just the air that is purged is recirculated back into the system.

the reason you are having stumbling issues is because you are losing air that has already been metered and calculated for by the mafs. the ecu determines the amount of fuel based on that metered air. by venting to atmosphere after the mafs you are losing some of that metered air causing a rich situation which you see with your stumbling issues.

venting to atmosphere is just a sound...is it really that important vs. having the car run properly like it's supposed to?
 

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99 s turbo
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97 Posts
Discussion Starter · #4 ·
your recirc valve is a bov. it's just the air that is purged is recirculated back into the system.

the reason you are having stumbling issues is because you are losing air that has already been metered and calculated for by the mafs. the ecu determines the amount of fuel based on that metered air. by venting to atmosphere after the mafs you are losing some of that metered air causing a rich situation which you see with your stumbling issues.

venting to atmosphere is just a sound...is it really that important vs. having the car run properly like it's supposed to?

yea iv been doin alot of readin on this subject, but should it run so bad at idle, could this be a sign that the dump valve is leakin?
 

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2006 Forester XT
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657 Posts
It is definitely an air metering issue - either the BOV is passing all the time and is now leaking metered air to atmosphere, or the hose is still leaking air in and isn't sealed.

Cover the BOV outlet while idling.....

Put your thumb over the hose end.....
 

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2004 Forester XT '06 STi 6MT
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707 Posts
yea iv been doin alot of readin on this subject, but should it run so bad at idle, could this be a sign that the dump valve is leakin?
yes. either that or whatever you used to plug the hole on the turbo inlet is also leaking.

honestly do yourself a favor and put the recirc hose back on :)

edit: if it's not even idling correctly then you have a leak somewhere.
 

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99 s turbo
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97 Posts
Discussion Starter · #7 ·
i did put straight back on, but i tried what stealth said today, about covering the bov end, that did help, i also noticed that the dumpvalve was open on idle and when i put my hand infront of it i can feel the air pushing out, only when i rev the engine quite hard thats when the dumpvalve shuts and when i release it opens, but arnt they supposed to stay shut until i let of the accelerator, also it runs fine when the recirc pipe is connected it only runs crap when the pipe is off.
 

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Official sf.org decal guy
2006 FXT
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12,366 Posts
i did put straight back on, but i tried what stealth said today, about covering the bov end, that did help, i also noticed that the dumpvalve was open on idle and when i put my hand infront of it i can feel the air pushing out, only when i rev the engine quite hard thats when the dumpvalve shuts and when i release it opens, but arnt they supposed to stay shut until i let of the accelerator, also it runs fine when the recirc pipe is connected it only runs crap when the pipe is off.
That's why I didn't understand why it was struggling at idle.
 

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99 UK S-turbo
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8,566 Posts
Did you block the port out the BOV, that will definately be open at idle (as it should be)....

You can't use the stock part as VTA as it opens at part load for fuel economy and will be open at idle by the vacuum from the manifold.

Simon
 

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04 Forester 2.5XT
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107 Posts
Did you block the port out the BOV, that will definately be open at idle (as it should be)....

You can't use the stock part as VTA as it opens at part load for fuel economy and will be open at idle by the vacuum from the manifold.

Simon
did a search and found this thread. You're saying that an aftermarket BOV that doesn't open during idle and part load should be ok at idle? Obviously when you're on the throttle and let off you'll go rich briefly from dumping metered air but I'm curious about idle. I highly doubt I would dump mine because of the sleeper effect. again, just curious.
 

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99 UK S-turbo
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No I'm saying a VTA (some aftermarket BOV are recirc) will not (or at least should not) be open at idle or part load......

Simon
 
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