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Discussion Starter · #1 ·
Hello all, I have recently purchased a 2016 Forte5 SX A/T. I'm loving the car so far, and the first 'mod' I have done is to disconnect, then later fully remove, the recirculation hose going from the BOV to the intake. I love that blow off sound, and everything has been fine for the week and a half or so that I had it disconnected. However today I have noticed an odd hissing sound coming from the engine when I accelerate, and it's quite loud. Upon checking out the engine bay, I have noticed that there is quite a bit of air coming out of the BOV when the engine is revving. The car doesn't feel quite as peppy as it used too, but I also haven't noticed any surging or sudden loss of power that others have reported when the BOV goes bad, and the sound goes away when I reattach the hose.

So is it normal for the BOV to just leak air like this? Or should it stay tight and only let out air when the throttle is released?

I took it to the dealer, and they said the sound was normal, despite my insistence that this new sound only started happening today.
 

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The hissing sound is normal, that is the turbo aspirating (like "charging"). In these cars usually happens between 1750 - 2000 RPM. When you change the the recirculating air to BOV, you will heard more air from the chambers. I don't heard it too much when the traffic is high or the radio is on because I haven't removed the hose from the intake (the dealer is fixing one of my tail lights and I don't want to mess with anything for now), but at night time I can heard it clearly. If you need more info about turbos and BOV, I recommend this video:

 

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Discussion Starter · #4 ·
My concern is that when I first removed the hose, aside from the blowoff 'phhhsss' when I let off the gas, there was no change in sound coming from the engine bay. I've been running like that for about 2 weeks, and suddenly today, near the end of a 30 mile drive, I noticed the sound, it's rather loud and wasn't there before. Perhaps hissing isn't the best way to describe it, but it's certainly sounds like air rushing out of somewhere, and it seems like it's coming from the BOV. I had someone rev up the engine to about 4000 RPM or so and hold it there for a few monents while I felt around the BOV outlet, and there was definitely a lot of air coming out.

So my question is: Is the BOV supposed to let out air when the engine is accelerating, or just when you let off the gas? Specifically, can the BOV operate in an intermediate state, only opening slightly to let out a little air, or do they usually only operate in a fully open/fully closed state?
 

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My concern is that when I first removed the hose, aside from the blowoff 'phhhsss' when I let off the gas, there was no change in sound coming from the engine bay. I've been running like that for about 2 weeks, and suddenly today, near the end of a 30 mile drive, I noticed the sound, it's rather loud and wasn't there before. Perhaps hissing isn't the best way to describe it, but it's certainly sounds like air rushing out of somewhere, and it seems like it's coming from the BOV. I had someone rev up the engine to about 4000 RPM or so and hold it there for a few monents while I felt around the BOV outlet, and there was definitely a lot of air coming out.

So my question is: Is the BOV supposed to let out air when the engine is accelerating, or just when you let off the gas? Specifically, can the BOV operate in an intermediate state, only opening slightly to let out a little air, or do they usually only operate in a fully open/fully closed state?
Well I'm not mechanic but this is what I can deduce. The air will come out from every where, as you can see in the video the air that is passing through a set of chambers. Remember that the hoes detach is just a "hack", not a performance BOV. You heard the sound because the hoes has bigger hole, the amount of air that is passing trough is more and the turbo will send a punch of air while the throttle and manifold are moving it to the engine. The air that isn't used, either by removing you pedal or just because the hole in the throttle chamber is smaller than the air that has been sent, needs to get out to some where but can't come back to the turbo. In summary, consider you have If you have a straw in form like Y. You blow air from one end, it will split into the other two ends. That is basically what is happening. As I mentioned before, if don't what to heard the louder escape then you need to install a performance BOV.
 

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Holding the rpms at a steady 4k will keep the bov open. It does that to let the pressure out since there is no boost built up and no load.
 

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Discussion Starter · #8 ·
So for an update about the odd sounds I have been hearing. Based on what people here have been saying, and the dealership also saying everything sounds normal, I reconnected the recirculation hose and was ready to leave it at that. Everything was quiet again.

However the loss of power still concerned me, and my fuel economy was starting to get worse and worse. It felt like the engine was working harder than it used to. Also the fact that when I first removed the recirculation hose everything was fine and quiet(aside from the 'PSSSSHH' sound when letting off the gas, of course) for 10 days or so, then suddenly getting that loud sound of rushing air when accelerating, was bugging me. So I removed the hose again and drove around for a bit, listening closely to the noises it made. It was definitely louder now, and was starting to make an odd whistling noise. It wasn't the turbo whine, it was something separate. I had also noticed the BOV sound was getting more and dull. Instead of the crisp 'PSSSHH' sound it used to make, it was very dull and sometimes not audible at all over the rushing air noise.

So I decided to remove the BOV to double check that the diaphragm wasn't torn or anything, and this is what I find:

Finger Gas Electric blue Plastic Toy


That little black bit in the center had somehow popped out and got wedged in at an angle, preventing the diaphragm from fully seating and letting a lot of air rush out. I removed that plastic piece and inspected it for damage, and aside from small scratches, seemed to be fine. I put it back in, making sure it is flush with the surface and firmly in place then put everything back together.

Finger Gas Nickel Electric blue Auto part


Then I went for a drive, sans recirculation hose...and everything is perfect again! That rushing air sound is gone, the BOV is loud and crisp when blowing off air. The engine doesn't feel like it's working so hard anymore and the power is back again, and my fuel economy has shot back up to normal. It's been over a week now and everything seems to be working as it used to. Also, just to be sure, I had someone rev the engine like last time while I held my hand near the BOV, and didn't feel any noticeable amount of air coming out.
 

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I see a piece of plastic that needs to be eliminated.
 
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