Hissing sound (not brake booster) (1 Viewer)

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So I’ve got a constant hissing noise while the rig is running and it continues a second or two after the rig is shut off. It sounds as though it’s coming from under/inside the intake manifold. It could have been there since I’ve had it for all I know. You gotta have your head pretty close to the upper intake to even hear it.
EGR is completely gone with block off plates and every vacuum port is capped. Charcoal canister is also gone. Brake booster is brand new OEM from a different issue. PCV grommet and all hoses are new in the last 3 months including the big intake hose. I’ve pulled the booster hose and temporarily capped it to eliminate that as a cause. Before I pull the upper intake, Are there any other ports underneath there that could be leaking?Suggestions are welcome. The rig runs great with zero problems. Just this weird noise.
 
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Constant with the engine running. Most clearly heard on drivers side with your ear close to the upper intake, 2-3 inches Forward of where the booster hose attaches to the barb.

Edit: only happens in run condition
 

flintknapper

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Constant with the engine running. Most clearly heard on drivers side with your ear close to the upper intake, 2-3 inches Forward of where the booster hose attaches to the barb.

Edit: only happens in run condition

So....can only be from Vacuum or Pressure. Pressure should be easy to find with a sprayer and soapy water (if not on a hot engine part), vacuum might be detected by using an unlit propane torch. Run it along lines, intake, throttle body etc....engine will rev slightly if any gets into the air intake system.

Mechanics stethoscope might help pin point it as well.
 
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I was gonna try propane in the morning. Already did the stethoscope thing and it was useless. All I heard was air movement all over the intake. Weird thing is it sounds like a big ass leak with your head close to the intake. I should add that the engine almost stalls when the oil cap or pcv hose is pulled off. So I wouldn’t think it’s a large leak
 

flintknapper

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Constant with the engine running. Most clearly heard on drivers side with your ear close to the upper intake, 2-3 inches Forward of where the booster hose attaches to the barb.

Edit: only happens in run condition

Kind of sounds EGR related...but there are a plethora of hoses underneath the upper intake around that area as well.
 
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If the EGR was still there that would have been my go to as well. I’ve capped all the vac ports on the top of the TB related to EGR and evap. Is there anymore ports hidden underneath I missed? According to the vac diagrams and pictures I’ve seen on here all the junk that’s underneath is just dead weight if everything up top is capped off.
 
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There is vacuum lines underneath that need to be taken care of they could be leaking and creating noise if came unplugged, what did you plug when you pulled the charcoal canister because it feeds in to the intake through a valve, there is vacuum line under the tps sensor that has to stay, and you need one to feed the fps on the fuel rail. Could be the seal on the booster at the check valve.
 
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So I’ve got a constant hissing noise while the rig is running and it continues a second or two after the rig is shut off. It sounds as though it’s coming from under/inside the intake manifold. It could have been there since I’ve had it for all I know. You gotta have your head pretty close to the upper intake to even hear it.
EGR is completely gone with block off plates and every vacuum port is capped. Charcoal canister is also gone. Brake booster is brand new OEM from a different issue. PCV grommet and all hoses are new in the last 3 months including the big intake hose. I’ve pulled the booster hose and temporarily capped it to eliminate that as a cause. Before I pull the upper intake, Are there any other ports underneath there that could be leaking?Suggestions are welcome. The rig runs great with zero problems. Just this weird noise.

I think I have the same noise. My rig also runs great with zero issues. Pair and EGR deleted.
I think it is just the flow of air through the IAC.

Think about it, if it was a vacuum leak it would be a massive one and the engine would run like total s***, but mine, and you state yours, run just fine!
 

flintknapper

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Upper Intake1.jpg
 
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pretty sure it’s not any of those lines. I’ve capped all circled in red. All that other crap is long gone.

The only stuff left is the FPR circled in green, and I’ve replaced the four vac hoses associated with it.

I just can’t remember if there was anything else under there I had capped at one point.

Thanks all for the suggestions. I’ll dig in a little more tomorrow. Just don’t feel like pulling the upper intake again. Especially in 90 degree heat.
FC16FCFD-0F26-4800-8BF5-F16F43B42FE0.jpeg
 
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Yeah, been following your thread on that. I’ll be referencing that and a few others when/if the time comes.
 

brettk

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We’re you able to ever to figure this out? I’ve got a pretty nice leak at the fitting between the intake and the brake booster hose. I plan to put some ultra grey on the threads to see if that fixes it.
 
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How is the PCV valve? Does the hissing change if you remove the oil cap with the engine running? If you try to remove the cap with it running and it is under lots of vacuum it may be a faulty PCV.
 
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We’re you able to ever to figure this out? I’ve got a pretty nice leak at the fitting between the intake and the brake booster hose. I plan to put some ultra grey on the threads to see if that fixes it.
Yeah, mine ended up being the plug I put in where the EGR temp sensor used to be. A little more Teflon tape fixed it right up.
 

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