hissing Noice

nvrsunk02 · Nov 8, 2007

Noticed a hissing noise, that is coming from the engine compartment right behind where the passenger airbag is. When I first start up and run the truck in park, the noise is almost unheard. When I put the engine into any gear from Nuetral or park, I can hear like a pop, then the idle drops, and the hissing starts. It almost sounds like I have the hVAC blower on, or could be a vacum type sound also. Any ideas what this could be and if it is normal? (4.0L auto 2002 4x4),

IMenriched · Nov 8, 2007

nvrsunk02 said:
Noticed a hissing noise, that is coming from the engine compartment right behind where the passenger airbag is. When I first start up and run the truck in park, the noise is almost unheard. When I put the engine into any gear from Nuetral or park, I can hear like a pop, then the idle drops, and the hissing starts. It almost sounds like I have the hVAC blower on, or could be a vacum type sound also. Any ideas what this could be and if it is normal? (4.0L auto 2002 4x4),

vacuum leak in the climate/ heater control somewhere.

hope that helps

nvrsunk02 · Nov 9, 2007

That is what I originally thought it was too. I also noticed that the heater/blower housing is cracked. But, when I noticed the pop when i go from neutral to drive and the drop in idle, I am having trouble seeing how that is related to the HVAC controls.

woodyedmiston · Nov 9, 2007

There is a little (and fragile darn it) fitting under the hood that all your heater hoses run through. It has a vacumm pot on top of it that controls the flow of water into your heater core. A vacuum line runs from it and under your dash to the heater contol. Hence the source of the noise most likely. If something is cracked a squirt bottle will tell you if the leak is coming from that point. All the jerking and changes in motor noise are because somehow it is seeing a vacuum leak and trying to compensate or quit.

(If your truck is a few years old I suggest changing out the fragile little plastic part, the one under the hood, every once in a while. Mind broke off, dumped the water and overheated my motor before I could say squat!)

nvrsunk02 · Nov 12, 2007

I think I found what your talking about. Its on the passenger side towards the front of the engine, right near the drive belt? Anyway, its burried down in there but it does look like it has 2 vaccum type ports on it, one towards the back (heater core side), and one towards the front (radiator side) that points up. There is a tube connected to the port on the back, but nothing connected to the one up on the front. Should there be something connected to it? It doesnt look like there are any loose hoses hanging around. Any idea where the hose comes from that connects to that port? Thanks!

hissing Noice

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