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Hissing Sound - WTF?

3K views 25 replies 11 participants last post by  CWest 
#1 ·
Okay - so I get rid of one noise, and get another.

Whenever I turn my engine off, I get this little hiss about a 1/2 second in duration. Definitely coming from the rear of the engine somewhere. The best way I can describe it, is if you squeezed the last little bit of air out of your inflatable sheep. It sounds like there is a little bit of air built up somewhere, and the pressure is being relieved after engine shut down.

If I listen really close I can hear it at low RPM's every time I make a small throttle change.

Anyone know what this might be?
 
#4 ·
Super Doody said:
condensate on exhaust?
If you mean condensation dripping on to the exhaust - no it's not that. This is definitely something mechanical.

You know like when you turn an air compressor off, and you relieve the remaining pressure out of the line. It's like that. It does it every single time I kill the engine.
 
#5 ·
SAR_Squid79 said:
Okay - so I get rid of one noise, and get another.

Whenever I turn my engine off, I get this little hiss about a 1/2 second in duration. Definitely coming from the rear of the engine somewhere. The best way I can describe it, is if you squeezed the last little bit of air out of your inflatable sheep. It sounds like there is a little bit of air built up somewhere, and the pressure is being relieved after engine shut down.

If I listen really close I can hear it at low RPM's every time I make a small throttle change.

Anyone know what this might be?
Damm, I don't have an inflatable sheep :p
 
#6 ·
well, to me it sounds like the same sound I get since the deckplate mod!! leave your passenger front door open and try revving from low RPM's and also shutting off the engine...if the noise sounds louder, it is your air intake! The reason is that the stock intake is connected into the pass front quarter panel and with the deckplate mod it seems like that acts to amplify the sounds...just my .02

Doug
 
#8 · (Edited)
That could be it - it could be something totally normal, and I'm just being paranoid. The noise is considerably louder when I kill the engine with my door open.

Tour4fun2000's Signature reminded me of another identical sound to the one I'm hearing. -A Turbo Blow-Off Valve.

Could it be pressure bleading out of the Supercharger or something?




...I was actually kind of hoping it was my exhaust manifold - then I could justify to the wife, getting the JBA Headers that I want! :D
 
#11 ·
Okay -
I went out to my truck started it, popped the hood, and then killed the engine by disconnecting the MAF sensor so I could listen to the sound from right there.

I checked all of my hoses and connections, and everything seems okay, but after starting and killing the engine a few times, I localized the sound to the area of the Throttle Body.

Upon further inspection, the noise actually sounds more like something SUCKING air, rather than leaking air as originally suspected. The sound is definitely coming from the TB area - maybe behind/under the TB.

:confused: :confused: :confused:
 
#13 ·
SAR_Squid79 said:
Okay -
I went out to my truck started it, popped the hood, and then killed the engine by disconnecting the MAF sensor so I could listen to the sound from right there.

I checked all of my hoses and connections, and everything seems okay, but after starting and killing the engine a few times, I localized the sound to the area of the Throttle Body.

Upon further inspection, the noise actually sounds more like something SUCKING air, rather than leaking air as originally suspected. The sound is definitely coming from the TB area - maybe behind/under the TB.

:confused: :confused: :confused:
Check that vacuum cap that is on the rear side of the SC'er inlet/TB outlet. There should be a 1/4" cap back there. You can also spry carb cleaner with it running to check for vacuum leaks. It will change idle speed if it sucks any in through any leak.

Side note-What did you do about the cardigan joint?
 
#14 · (Edited)
wisctaco04 said:
Side note-What did you do about the cardigan joint?
I found a place right down the road, that will pull the D-shaft, Rebuild or Replace the Double Cardan joint, and the other U-joints in 1 day for $180. I'm gonna have them fix it when I get back from San Diego. Unitl then - I'm greasing them shits every few days to keep them quiet.


...where do I spray Carb Cleaner?
 
#15 ·
SAR_Squid79 said:
...where do I spray Carb Cleaner?
On any and all connections that the vacuum lines make. I would just start it and gently spray along the lines and at the connections.

I don't recall where we ran the lines to the boost guage and the FTC but make sure one of then didn't release and fall under the TB.
 
#17 ·
Yup- If I remember, when I had my belt and TB off of the SC'er and I spun it by hand you could feel the pressure the rotors built and then release. You might just be hearing that on shut-down. Is this new or old noise? New since your windows are down? IAC valve flowing good?(the white one on the underside of the TB)
 
#18 ·
Yeah - actually that IAC valve was one of my 1st troubleshooting points. It's still good, and I have a spare anyway.

LOL - My truck has been making so many damned noises lately that I actually don't know if it's a new noise - I think maybe I've heard it but never payed any attention to it before. At this point if a spider gets in my truck and farts, I'm gonna hear it and think there's something else wrong with my truck.
:xcrazy: :aahg:
 
#21 ·
O.K. After going out and starting my truck and driving it home, then shutting down and restarting several times, hood open, hood closed...doors open doors closed, deck plate open, deckplate closed, all of the above, none of the above... I am fairly certain this is the noise I hear too! Mine sounds different from other trucks w/ open air boxes that I have heard,( when you rev from low idle or start or especially shut off the engine it almost sounds like ripping the vacuum seal off of a coffee can or pringles or something) but it has sounded that way since the day I cut the hole there, and when the SC bolted on, it amplified it due to the higher volume of air being moved. As for the sound at or near the throttle body, still could be intake related, and that is probably where you are hearing, not necessarily where it is coming from. Try closing your deckplate then repeat you diagnostics...Again, listen in the passenger side door by the hinges...

I could be wrong, but I would put a $20.00 on this wager now!!!! :D :D


Doug
 
#22 · (Edited)
So I keep getting CEL Code P0171.

I wonder if it's related to this hissing sound?
:banghead:

**EDIT**
Now that I've thought about it - I think I might have "F"-ed up my MAF sensor by disconnecting it to kill my engine the other day. If so - That's about a $100 screw up.
 
#24 ·
SAR_Squid79 said:
So I keep getting CEL Code P0171.

I wonder if it's related to this hissing sound?
:banghead:

**EDIT**
Now that I've thought about it - I think I might have "F"-ed up my MAF sensor by disconnecting it to kill my engine the other day. If so - That's about a $100 screw up.
Test it using the directions in the FSM. You have an ohm meter you should be good.
 
#25 · (Edited)
wisctaco04 said:
Test it using the directions in the FSM. You have an ohm meter you should be good.
Thanks for the heads-up. I really need to read the FSM more.

So anyway - I tested it:



It says I should get 2.2 - 2.7 K-Ohms of resistance.
I got 6.02 K-Ohms.

So I guess I need a new MAF sensor, and that's the answer to my CEL.


http://www.tacomaterritory.com/forum/showthread.php?t=34957


still got the hissing sound, though...
 
#26 ·
Dug deep on this one...


Same issue, turn off truck and hiss for 2-3 seconds. Narrowed it down in the parking lot at lunch today to drivers side firewall area.

Diggin more this weekend. I'm assuming over the last 7 years you found something???
 
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