WHOOOSH Sound Under Boost, Normal?

[bwhite8889]

I recently had the VCT cam phaser job done on my 2018 Expedition. When I got it back I noticed a WHOOSH/hissing sound on the driver’s side while under turbo boost. It doesn’t sound terrible, almost like compressed air being released.

Through some research I decided to replace the Blow Off Valve (BOV). To my surprise, when I pulled the old one off, the entire piston/o-ring assembly appeared to be missing (pictured on the left-side of the photo). With the new one on I took it for a test drive. I still get the sound under boost but it seems slightly quieter, doesn’t activate as quickly (takes more boost before I’ll hear it) and the turbo seems slightly more responsive.

I’m no turbo expert, but here’s my attempt at an explanation… I assume that they forgot to install the o-ring piston assembly at the shop. So when I was under boost (any amount of pressure), the excess boost would pass right on by this assembly, thus making the whoosh sound all the time. With the new assembly, it has to build enough pressure to push that piston down before it will bypass. Am I thinking about this correctly?

Another dumb question, how critical is this assembly to the turbo system? It wasn’t triggering a code with the piston missing, and the hissing/whoosh didn’t entirely go away even with the new one installed (unless I installed it incorrectly? Can’t imagine that I did, it was only two 8mm bolts). Someone smarter than me might be able to explain exactly what this thing does and if that whoosh noise I’m hearing under boost is totally normal.

 

[Going_Going_Gone]

Interesting...Are all the clamps on your CAC tube connections tight?

 

[bwhite8889]

I believe so. Hard to say if the sound is just normal turbo noise but sure glad I found the BOV piston/seal issue.

 

[99WhiteC5Coupe]

I recently had the VCT cam phaser job done on my 2018 Expedition. When I got it back I noticed a WHOOSH/hissing sound on the driver’s side while under turbo boost. It doesn’t sound terrible, almost like compressed air being released.

Through some research I decided to replace the Blow Off Valve (BOV). To my surprise, when I pulled the old one off, the entire piston/o-ring assembly appeared to be missing (pictured on the left-side of the photo). With the new one on I took it for a test drive. I still get the sound under boost but it seems slightly quieter, doesn’t activate as quickly (takes more boost before I’ll hear it) and the turbo seems slightly more responsive.

I’m no turbo expert, but here’s my attempt at an explanation… I assume that they forgot to install the o-ring piston assembly at the shop. So when I was under boost (any amount of pressure), the excess boost would pass right on by this assembly, thus making the whoosh sound all the time. With the new assembly, it has to build enough pressure to push that piston down before it will bypass. Am I thinking about this correctly?

Another dumb question, how critical is this assembly to the turbo system? It wasn’t triggering a code with the piston missing, and the hissing/whoosh didn’t entirely go away even with the new one installed (unless I installed it incorrectly? Can’t imagine that I did, it was only two 8mm bolts). Someone smarter than me might be able to explain exactly what this thing does and if that whoosh noise I’m hearing under boost is totally normal.

View attachment 77828

I had an unusual sound begin after one the the repairs to my 2015 Expedition at a Ford dealer. I replaced several items with OE parts (but not the blow-off valve) with no resolution. The dealer claims they cannot hear the noise (although it can be heard at various speeds) - when I lift my foot from the gas pedal.

The sound is explained well here - but no resolution for me or the original poster: https://www.expeditionforum.com/threads/occasional-hooting-sound.53031/

Does this blow-off-valve mount near the bottom of the assembly, behind the radiator bottom?

I’m wondering if I have the same issue as you with a defective valve?

 

[bwhite8889]

That’s not the sound I have, mine sounds more like compressed air being released.

However if you want to try to replace the BOV, on my expedition it is right behind the IC. Two 8mm bolts holding it on, I didn’t even need to disconnect any hoses.

for me it was on the drivers side of the IC and only took about 20 min to replace. It has a single 12 volt plug going to it.

 

[Soliyou]

That’s not the sound I have, mine sounds more like compressed air being released.

However if you want to try to replace the BOV, on my expedition it is right behind the IC. Two 8mm bolts holding it on, I didn’t even need to disconnect any hoses.

for me it was on the drivers side of the IC and only took about 20 min to replace. It has a single 12 volt plug going to it.

It seems that the newer OEM BOV is manufactured by Standard and it looks similar to your original one. See this link:
https://www.carid.com/standard/turbocharger-bypass-valve-mpn-tbv1008.html

a faulty BOV can lead to boost leak. However with a hissing sound you probably have a clear boost leak. I would double check all air ducts since they all have to be removed for VCT replacement. I would just take it back to the dealer who did the VCT work.

 

[bwhite8889]

Thanks for the link! Either way I’m glad I replaced because my old one because the green o-ring had several tears in it (see attached photo). Also attaching a video of how to access for the previous poster.

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All hoses appear to be tight and there doesn’t seem to be a loss in turbo performance. Also there’s no check engine light. Am I just perhaps hearing normal boost blow off? It’s so hard to tell what’s normal with these turbo engines since a lot of people modify them to make it louder than stock.

 

[bwhite8889]

Turns out it wasn’t normal and was the turbo going bad. Had the turbo and all related hoses replaced. Sound gone. There is a VERY faint version of the sound under heavy boost, this is what I think people refer to as the normal boost noise.

What I had before was loud and probably related to a leaky wastegate if I had to guess. Either way, problem solved. Also noticed a major performance improvement.

 

[Going_Going_Gone]

Another positive outcome. Lucky for you that the parts your vehicle needed were available.

 

[MetallicaGray]

Did it sound like a vacuum sucking air? That’s what mine sounds like