Hiss after engine shutoff?

[5.04Life]

Hey guys,

I don't post on here very often but when I shut my car off I hear a distinctive hiss come from under the hood, wondering if this is normal or vaccuum leak or something else? thanks

Chad

 

[battyice]

Sure it's not your air conditioning?

 

[HISSIN50]

i saw my name and had to come in. i would agree with above. when the motor is off, there should be no vacuum, so no leak.....

 

[5.04Life]

Even if the AC does not work? It hasn't worked since I've owned it, last year or so. Also it hisses right as you shut it off, as in click - hiss, dunno if that helps or not. Thanks

 

[blk92stangg]

In mine condesation off the air con pipes drips on the headers making the hissing sound. The refrigerant expanding in the system also makes a hissing kinda sound too, as mentioned above.

 

[HISSIN50]

ok, i gotcha. in the winter (no a/c) i have heard the same thing. for me, it sounded like it came from the pass front (near the charcoal cannister). i asked a bud and he said it is normal (coolant or something). to me, it sounded just like a drop of oil hitting the exhaust). i never could pin point the source (even with a stethoscope).

i think Mike (Mustang 5L5 has posted that it is normal too).

good luck.

 

[crazy_canuck999]

I think it's a normal sound... it comes from somewhere near the water pump I think.

 

[Camman]

Its ur engine gasping after you turn the car off. It needs more air!! Quick run out and buy more parts so it will get more air!!! I tried telling that to the wife but she didnt buy it... therefore still stock

 

[Js5ohLX]

Lol that's funny, my wife didn't buy it either, I tried.

 

[MavericK5L]

its the PCV which is unplug.

Behind the upper intake

I did the same thing to me when I forgot to plug it back (oups)

 

[QDRHRSE]

All my 5.0 cars have made that noise. I always thought it had something to do with modifying the air intake...like the motor still has a little vacuum after it shuts off and sucks in a little air.

 

[ECU5.0]

you guys sure its not the fuel lines releasing pressure back to the tank? i know that the fuel pump is supposed to stay on for a few seconds after you shut the car off and that could be the noise. i know when my fuel pump relay went bad and my pump wasnt shutting off you could hear a hissing coming from under the hood and after a quick inspection it was coming from the fuel line

 

[Infiniti 7000]

dude its normal I read your sig. and saw your mods. You have a fenderwell intake which means its no restriction, my stock intake on my notch did that but not very noticably, your aftermarket intake is no restriction just a tube with the mass air meter and a filter its normal. Its your intake depressurizing, it should only last for a matter of a split second or so after the car is off, depending on how hard you just drove it but don't worry it shouldnt be a problem.

 

[BlackFox5.0]

When I plugged up the tube that goes from the valve cover to the TB I was getting a hissing. it was because the intake was sucking air from the PCV and there was no other place for it to get air, so it got it from the dipstick, which made a hissing after I shut the car off. I fixed that problem now

 

[Mavrick]

When I plugged up the tube that goes from the valve cover to the TB I was getting a hissing. it was because the intake was sucking air from the PCV and there was no other place for it to get air, so it got it from the dipstick, which made a hissing after I shut the car off. I fixed that problem now

How did you fix that problem?

Mine hisses too, it might have been the PCV because i easily removed it, and put it back in the rear of the intake nice and snug. I thought it was a vac leak, havn't started it for a while but ill find out in a couple weeks!

 

[BlackFox5.0]

If the valve cover hose is taken off, and plugged it will create vacuum in the crankcase and will grab air from any place it can. In my case it was from the dipstick. I put on a breather because when i hit boost it owuld pressurize my crankcase which I didn't want. this is just a temp fix, i am going to make a catch can for the pcv so I can put it on the inlet of my blower and not get oil inside it

 

[Mavrick]

Ah i must have misread your post. I didn't remove my breather so that isn't a fix for me. Hopefully mine is just the PCV acting up, easy fix!!

 

[5.04Life]

Alright thanks for all the replies guys, that helped me understand it a bit more.