Hum noise after the truck is shut off...
#1
10-09-2006
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Hum noise after the truck is shut off...
Well, this has been going on pretty consistantly for about a month now. When i shut the truck down i get this "HMM" hum noise that lasts for about a full second. I did find out that its coming straight from the intake, almost like its trying to push air back out. It has nothing to do with the A/C either, suggestions? 
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10-09-2006
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#6
10-10-2006
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10-10-2006
#8
10-10-2006
Originally Posted by rwenzing
It sounds like it might be air rushing in to bring some device or the manifold plenum itself from 20" idle vacuum up to atmospheric pressure after the engine is turned off.
that sounds way too complicated for me! sounds like you are talking in Rocket Science language....
#10
10-10-2006
The manifold vacuum of a healthy stock engine idling in N or P near sea level is roughly 20~21". It is less as you go up in elevation.
This vacuum is maintained by the engine pumping against the closed throttle plate with a variable "leak" through the IAC to control the idle speed. When the engine is turned off, the pumping stops and air will leak into the manifold plenum and into any vacuum controlled devices wherever it can until the system vacuum becomes zero (equal to atmospheric pressure).
The leakage could be through open intake/exhaust valves, through the IAC or through any kind of vacuum leak. It takes a short time to bleed the system vacuum up to atmospheric just as it takes the engine a short time to pull the vacuum when it is started.
This vacuum is maintained by the engine pumping against the closed throttle plate with a variable "leak" through the IAC to control the idle speed. When the engine is turned off, the pumping stops and air will leak into the manifold plenum and into any vacuum controlled devices wherever it can until the system vacuum becomes zero (equal to atmospheric pressure).
The leakage could be through open intake/exhaust valves, through the IAC or through any kind of vacuum leak. It takes a short time to bleed the system vacuum up to atmospheric just as it takes the engine a short time to pull the vacuum when it is started.
#11
10-10-2006
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#12
10-10-2006
Originally Posted by rwenzing
The manifold vacuum of a healthy stock engine idling in N or P near sea level is roughly 20~21". It is less as you go up in elevation.
This vacuum is maintained by the engine pumping against the closed throttle plate with a variable "leak" through the IAC to control the idle speed. When the engine is turned off, the pumping stops and air will leak into the manifold plenum and into any vacuum controlled devices wherever it can until the system vacuum becomes zero (equal to atmospheric pressure).
The leakage could be through open intake/exhaust valves, through the IAC or through any kind of vacuum leak. It takes a short time to bleed the system vacuum up to atmospheric just as it takes the engine a short time to pull the vacuum when it is started.
This vacuum is maintained by the engine pumping against the closed throttle plate with a variable "leak" through the IAC to control the idle speed. When the engine is turned off, the pumping stops and air will leak into the manifold plenum and into any vacuum controlled devices wherever it can until the system vacuum becomes zero (equal to atmospheric pressure).
The leakage could be through open intake/exhaust valves, through the IAC or through any kind of vacuum leak. It takes a short time to bleed the system vacuum up to atmospheric just as it takes the engine a short time to pull the vacuum when it is started.
#13
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Thanks for the reply Bob, i'd like you hear it in person at the meet if you can. I still am under warranty, so if its something that should be fixed, i might as well take it in and have them fix it while i still can.
I was talking to Nick (NicksterSVT) and he thought it was because the stock intake assemble has baffles that stop this hum sound. And since i put that MAC intake on, it came with no baffles so thats why the sound is so much more noticeable. Very weird, but possible.
Originally Posted by 04lvl2
I get a noise sometimes when I shut mine off too Mark, you dont hear it with the stock airbox as it is closed up. We should be able to figure it out at the meet for sure.
#14
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Originally Posted by 01xltranger4x4
Thanks for the reply Bob, i'd like you hear it in person at the meet if you can. I still am under warranty, so if its something that should be fixed, i might as well take it in and have them fix it while i still can.
I was talking to Nick (NicksterSVT) and he thought it was because the stock intake assemble has baffles that stop this hum sound. And since i put that MAC intake on, it came with no baffles so thats why the sound is so much more noticeable. Very weird, but possible.
I was talking to Nick (NicksterSVT) and he thought it was because the stock intake assemble has baffles that stop this hum sound. And since i put that MAC intake on, it came with no baffles so thats why the sound is so much more noticeable. Very weird, but possible.
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