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Matt
Dodge Dakota
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6/25/2003
00:13:17
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 Subject: Hissing noise! Please help!
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Ive done some extensive research on here, and I havent found anything to completely explain my noise. This is with the hood up, and the engine running, and leaning over the passenger side fender. At idle in park, there is no noise... however, if you pull on the throttle cable to give it some fuel, a hissing noise starts. It also does it a lot louder in reverse or drive. At first, I thought it was coming from my aftermarket intake, but recently, I listened more carefully, and its coming from another area, more towards the front of the engine bay, and sounds almost like its coming from the radiator or somewhere in the cooling system. It does it mainly at start up, and after the engine gets hot, it stops. The engine doesnt over heat, no leaks, etc, and I dont have any other problems, Im just wondering what it is. Thanks for your help!
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Ray Kolbe
Dodge Dakota
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6/25/2003
11:40:19
|  RE: Hissing noise! Please help!
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Hmm...I was thinking it was your filter also. Could it be the TB? Take off the filter and then listen closly to the TB, see if its coming from there.
Check your hoses also...im no pro, but thats what i can suggest.
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bdholsin
Dodge Dakota
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6/25/2003
12:03:03
| RE: Hissing noise! Please help!
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It may be the orifice valve in your AC system. The compressor compresses the refrigerant to a high temperature high pressure fluid then passes it through the condenser which rejects heat. Now you have condensed liquid. After the condenser it passes through a metering device (such as your fixed orifice valve) and is sent to the evaporator, via the filter/drier to remove excess oil and contaminants that may damage your system, as a low temperature low pressure gas. The hissing you are hearing *could* be the refrigerant expanding through the orifice valve. If you run your AC while driving and then turn off the vehicle can you still hear the same hissing noise? Just my two cents to help you out. That's it for A/C 101 class.
By the way...after going through the evaporator the refrigerant is now a low pressure higher temperature gas and returns to the compressor. Didn't want to leave anyone else hanging in case they were wondering what happens after the evaporator.
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Matt
Dodge Dakota
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6/25/2003
14:02:01
| RE: Hissing noise! Please help!
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Matt my truck does the same exact thing. It hisses when its cold for about a minutes until the engine heats up. Mine hisses quietly when its in park or neutral but when put in R or D its louder. I had a friend hold the brake and put it in R while i listened for the noise. Found it coming from the aftermarket filter, both of the filters I tried. So its no big thing.
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Matt
Dodge Dakota
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6/25/2003
23:28:29
| RE: Hissing noise! Please help!
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Thanks a lot guys, I thought it was the intake too, but I listened to a friends 3.9, and its still there, just really faint. And come to think of it, it did get worse after about 100 miles after I put the intake on. I didnt reset the comp, so maybe it started after it learned something about the new found air. I like the TB idea, and the A/C idea makes perfect sense. If i figure it out, Ill post my findings, just for some future reference for people. Thanks again!
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BCDakota
Dodge Dakota
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6/26/2003
02:12:13
|  RE: Hissing noise! Please help!
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I have the same noise when engine is idleing but when I give it gas it almost disapears. It only does it when the engine is cold, after warm up it disapears.I've always just shrugged it off as a cold air intake prob but am curios to find out for sure.
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bdholsin
Dodge Dakota
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6/26/2003
07:37:23
| RE: Hissing noise! Please help!
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Matt,
I was just thinking...If you take off your cold air hat and look down on the throttle body do you see a rectangular plate that holds that cold air hat fastener? I removed my fastener retainer and installed an "S" bolt to reduce the restriction at the TB. This resulted in a bit of a sucking/hissing sound at the TB. Just another two cents from me. It isn't detrimental. I believe that it is the airflow becoming laminar as it rushes through the TB. One way, and I have not tried this yet, you may be able to reduce/eliminate the hissing sound is to "trip up" the laminar flow and introduce or creat a bit of turbulent flow right after the cold air hat. You can best accomplish this by tying a string across the cold air hat reinforcement beams. Maybe you will, maybe you won't want to try it. It is up to you. It depends on how much it is bothering you. The sound isn't detrimental to the vehicle performance or operation.
Good luck.
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