strange "hissing" sound

[tbomb]

my truck makes this strange hissing sound - kind of like steam escaping (i cant even remember if it always did this or not, but i get the feeling that maybe this isnt normal.)

it definately coming from the engine area, but im not sure if i just hear it through the firewall, or if i hear it through the a/c vents. it makes this sound when the a/c or fan is on and also when its off. when i step on the gas, it gets louder, but if i turn the radio on i really cant hear it.

i do have a kkm, and my first thought was maybe its just the kkm sucking air, but maybe its something else. could it be a vacuum leak?...if it is a vacuum leak, would i even be able to hear a vacuum leak?

im lost on this one guys. my truck is going in the shop in about 2 weeks for a 30,000 mile 'tune up.' and id like to have some suggestions for the guy to look at regarding this hissing noise.

thanks.

 

[mrboyle]

Sounds like a vacuum leak. The easiest way to find it is to take a can of carb cleaner (make sure its O2 sensor safe) and with the engine running spray around all the hose connections, the throttle body, intake, etc.. If you have a leak the engine will bog down (slightly) when you spray the carb cleaner on the leak.

 

[tbomb]

can you hear a vacuum leak though? i didnt think you could. im just gonna let the mechanic deal with it in a week or so - i really dont have the time.

 

[ok89]

I just noticed I have a hissing sound too. (just noticed cause i was actually driving windows up radio off) anyways here is the problem. At idle i get a hiss not really a whistle. This hiss goes away when i give her gas. The more gas the less hiss. This sound is coming from the engine compartment. Any ideas. Its still under warranty so i think im going to add it to the list of warranty work for Ford to take care of.

 

[jimbo74]

sounds like the a/c clutch engaging/disengaging

 

[jimmiecakes]

I'd have to think vacuum leaks as well. Especially for OK89....

As you step down on the foot feed, manifold vacuum "drops", i.e. approaches atmospheric pressure. The less difference between manifold "pressure" and atmospheric pressure, the less hiss.

"Some" aftermarket air filters "may" make a sound like this (YMMV), so listen carefully for the rough area of the source. O2 sensor friendly carb spray or (better yet) air intake system cleaner may help pinpoint the leak.

Yes WD40 will work but, AFAIK, WD40 contains silicon. For those not up on Algebra...... silicon+combustion=new O2 sensor(s).

 

[Kontrol-Trak]

Maybe you got a snake trapped in your A/C system ... j/k

 

[ChuckyD]

Had the same thing last month... it was a VAC leak. On my motor is was a small vac line that was loose right by the firwall. Just had to push it back in to where ever it was connected. I couldnt really see it i just fealt it and herd it get louder and quiter when i jiggled the lines.

 

[Cdexplorer]

I just got my truck back from Ford....$760 later It was in to get new brakes/emergency brakes but when I went to pick it up the service guy told me about a hissing noise under the hood. I had noticed it before but didn't know what it was. He knew exactly what it was...something near the firewall...a hose which has something to do with emissions. He said it's common for it to crack and then it makes this noise. It isn't a problem for the engine and the part is inexpensive but to replace it there's a lot of work to get to it so it's not really worth it unless it really bothers you. I wish I knew exactly what he said it was but I don't. I'll give him a call on monday and find out for you. May not be the same problem you have but it could be.

 

[ok89]

Well I know the little plastic T on the PCV valve has a little part broken off but it still sits on the PCV and attaches to the hoses fine. And the idle is as smooth as it has ever been.
Jim - Its not the AC clutch engaging and disengaging because I have had that problem for a while (system needs recharging)
Well is it possible that it could be something bad. We are getting ready to drive about 1000 miles up to Iowa and then another 1000 miles back so i dont want any suprises.

 

[jimmiecakes]

It isn't a problem for the engine

Sounds like a lazy mechanic.....

Not wanting to to sound too ****, a vacuum leak is both "unauthorized air" (air the ECM can't account for)and unfiltered air. A vacuum leak can upset fuel mixture, exhaust and evaporative emissions, crankcase ventilation and a whole mess of other stuff that can lead to the early demise of the motor in your ride.

Speaking for myself, if something is wrong with my car it just seems to keep smacking me in the side of the head every time I drive it 8^)

 

[X24]

my 98 does the hissing thing when i let off the gas. as soon as i take my foot off the gas i hear it (very noticable with the raido off) as the rpms get closer to idle it gets quieter. i have an appt. with ford for an overheating problem in 2 days and for the past couple days i have been making a list of TSB's and recalls that i want checked/fixed. I CAN'T BELIEVE HOW MANY TSB'S THERE ARE!! the more i think about it the more rediculous it gets. anyway, my list has about 20 or so things on it. they can keep it for as long as it takes to fix everything... i have another car to drive (ford probe V6... fun, but not as fun as the X). if anyone has any suggestions for things i should consider adding let me know. thanks

 

[tbomb]

whoa, i actually started this thread a long time ago...anyway, since july, i found out what the hissing noise is (for future reference): its just the rushing of air into the engine through the PLASTIC plenum. thats right, plastic. fords cheapening up its products, so youre gonna hear that hissing - its perfectly normal.

 

[Eg3395]

Hey guys I had the same problem first it started as a hissing sound almost as if steam is escaping from the front end of my car I looked and I try to follow it it was very light at first and then it was pretty loud when I got home from work I noticed the tensioner pully has a very slight wobble.
It really was not noticable so I let it go for about a week. Then I hear tapping sounded like an old motor t engine I look again pully is allover the place. Changed the whole assembly hissing is gone.