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Old 02-01-2011, 11:17 AM
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Help-Weird compression (air) noise when starting...

Need some help. Sorry I’m far from mechanical with anything on four wheels. I’ve done a search with no luck.

I’m wondering if I have a problem when I start my 05 Limited Hemi. When I turn the engine over and it’s about to start I hear a compression (air like) noise hissing for a second. It’s pretty loud. The Jeep is running just fine by it doesn’t sound normal. I only hear the sound the second the engine is about to start.

Any ideas? Maybe it’s just normal and I’m getting old and paranoid. I’m about to take it into the stealership for a routine service but I don’t trust them..
Thanks!
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Old 02-01-2011, 12:33 PM
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Re: Help-Weird compression (air) noise when starting...

sounds like an exhaust manifold leak.

and it might be small so once things start ot heat it goes away.
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Old 02-01-2011, 03:20 PM
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Re: Help-Weird compression (air) noise when starting...

Thanks, just might be onto something. I went out with a co-worker to investigate. It only makes the noise on the first start and then you have to wait about five minutes with the engine off for it to make the noise again during the next start.
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Old 02-01-2011, 08:28 PM
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Re: Help-Weird compression (air) noise when starting...

Doesn't sound like an exhaust leak, and it shouldn't go away that fast if it was. My v-6 does the same thing after i put the CAI on. I think it has to do with the EGR system reseting itself.
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Old 02-01-2011, 08:53 PM
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Re: Help-Weird compression (air) noise when starting...

Sounds like a possible leak within the A/C system's valve actuations (the bits that move the direction flaps etc)
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Old 02-01-2011, 10:05 PM
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Re: Help-Weird compression (air) noise when starting...

sounds like a vacuum leak to me....maybe in the brake booster line nor another vacuum hose.

Open the hood and have someone else start the vehicle and see if you can narrow down the area it is coming from....
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Old 02-01-2011, 11:55 PM
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Re: Help-Weird compression (air) noise when starting...

It appears to be coming from the right side halfway down the engine block (Hemi). Right side when standing in front. Itís intermittent and never repeats right away. Sometimes I can wait 5-10 minutes and it will repeat. Itís only ever heard a second or two after initial crank.

Had a mechanically inclined co-worker look at it today and he thought it might be the serpentine belt and or tensioner which was just replaced last summer. Had the wife start it a couple times tonight and to me it sounds a lot more like air compression sound. For what itís worth; the co-worker that looked at it tonight rebuilds mustangs as a side business and me well if I open the hood the wife calls 911.

Otherwise the beast runs great. Itís a í05 has 49k and the extended warranty just ran out in December. Concerned continued use might damage something more. Appreciate everyone comments!!! 1-2 more years and its WK2 time!!!
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Old 02-02-2011, 12:03 AM
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Re: Help-Weird compression (air) noise when starting...

So your man on the ground who "knows stuff" can't tell for sure? If thats the case, we're unlikely to be able to help via the interwebs Might be time to take it to a mechanic?
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Old 02-02-2011, 01:51 PM
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Re: Help-Weird compression (air) noise when starting...

Definitley not a vacuum leak as the engine idle would stumble and run very poorly. Does it make the sound when the engine is hot, you turn it off and then restart right away, or just after it has been sittiing ?
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Old 02-02-2011, 03:19 PM
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Re: Help-Weird compression (air) noise when starting...

Alot of this story doesnt add up further complicating any possible help from here.

you said "right side of engine block" then you say serp belt which is the front of the engine block. I would agree with robpp, especially considering where you say the sound is coming from, could be an exhaust leak.
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Old 02-02-2011, 03:47 PM
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Re: Help-Weird compression (air) noise when starting...

Quote:
Originally Posted by Scottina06 View Post
sounds like a vacuum leak to me....maybe in the brake booster line nor another vacuum hose.

Open the hood and have someone else start the vehicle and see if you can narrow down the area it is coming from....
im going to go with scott on this one. if you hear a hissing noise at first and it goes away it has to be a vacuum leak. that would def be my first guess.
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Old 02-02-2011, 03:52 PM
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Re: Help-Weird compression (air) noise when starting...

yep...or a hose collapses on startup because its wron and then opens up as pressure is built....

just a guess though....cause it happened to me after installing an intake manifold. The hoese look good...but are worn and collapse under pressure at startup.
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