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Discussion Starter #1
Alright. Like it states - sounds exactly like rod knock.
08 avenger 2.4
Start it up and there is an initial whirring, like an idler pully is going bad. The whirring stops and immediately turns into what can only be described as rod knock noise. However, I removed the serpentine belt and ran the car for a moment And the knock/whirring disappeared leading me to believe the knock is not in the crank. Initially thought it was the power steering pump, so I removed and replaced with no joy. Removed and replaced ac compressor - knock still present. I'm out of ideas now fellas. Anybody got anything else for me to try?
 

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The alternator has a centrifugal clutch pulley unlike a normal constant drive pulley, it does go bad and can make that kind of sound before completely going. It takes a "special tool" to replace the pulley once the alternator is removed from the car. Got a feeling that you may find your problem there.
Welcome to the Forumz, Drop by the check in page and introduce yourself and ride to the whole Forumz Family!

EDIT: I had that happen on my 04 T&C which uses the same type alternator pulley, But opted for a reman complete alt. due to the mileage on it.
 

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I've looked around for videos of these decoupler pulleys on the alternator, and I really haven't found one that sounds similar to mine. I'm telling you, if it weren't for the whir of a bad pulley noise, I would have sold the car for scrap. It legit sounds like really hard rod knock.
 

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YUP, same here! But as you posted without the belt on NO noise. And it is the only pulley left that is belt driven and a common 2.4 engine complaint.
 

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I know a decent amount about vehicles. I used to race micros and sprint cars. I've always worked and built my own stuff....but I'm seriously about to take this thing to a mechanic to find this noise unless you can tell me for certain that this tiny decoupler bearing can produce the sound of a piston rod making solid contact with metal. I'm talkin rock hard rod knock noise man.
 

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Last thought I can come up with is to check the crank pulley for devulcanization of the hub to belt ring, but that should have been pretty obvious to have seen with the work you already posted of doing.

EDIT: to combine to your last post..I thought my engine blew up and it was from the "decoupler" pulley. But I am in NY and you and 'Venger" are in Iowa, sight unseen I can not do as you request.
I pass along my best hopes you can nail down your problem, as you seem to have done an awful lot already with no joy on a fix yet.
 

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A stop at the check in page for an intro of yourself and also a quick read of forum how to's found there will give those answers to you.
EDIT look at support page at bottom of main forum page list for help in posting pics and vids
 

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Discussion Starter #9
Thabks for your help. Here's a youtube link to my avenger. It would be awesome if you let me know what you think of the noise.

 

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Is the A/C on while you are running it, you said you replaced the compressor. That is another one of the banging noise complaints of the early sedans(bad compressor), but should only "sound off" when in operation. That sound is quite harsh, but don't know how long this has been going on with you. As a former racer and DIY'er You should know that some sounds can be from any number of places. Recheck your crank pulley as that recording sounds of bang and scrapping noise also.(what I suggested before). You are going to have to go underneath and INSPECT parts for solid determination of the noise cause. I have offered 2 and suspect a third until you can confirm to me of these items. What I will NOT do is tell you to just change part X and that will be your fix, and I doubt very many members would do otherwise.
 

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Discussion Starter #11
The crank pulley is fine, and after I replaced the PS pump I used a stethoscope to determine the most noise came from the compressor. The knock does not change whether the AC is on or not. I don't know much about this specific compressor, but if it is like any others I've encountered, the clutch is failed engaged as there was no freewheeling. As stated, after replacing the compressor, the knock still lives.
 

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Well the only thing I can suggest is to pull the belt back of and hand spin pulleys and if compressor clutch is failed I have read posts of members reporting MULTIPLE short lifespan( i.e. NO lifespan) of compressor replacements, Bad internals. You just may end up at a reputable shop with this one.
 

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I would pick up an inexpensive automotive stethoscope to isolate the noise. If not, you can use an old shortened broom handle held against each unit. The other end held up to your ear. Just be careful when the engine is running during the test.
 

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Rain? I thought I saw on weather channel you MAY be getting SNOW!... GOOD LUCK and keep us posted to outcome!
 

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My AC compressor pulley is going out. I just spray some wd40 to determine if it's on its way out. I get a slight noise on cold starts but it I spray it with the wd40 it almost immediately goes away I read in the manual somewhere that you're supposed to grease the AC compressor. But that's nothing compared to the alternator! I've gone thru 3 alternators already. Lucky I've got a lifetime warranty on it.
 

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And make sure your pulleys aren't broken or banged up. In the video the belt shouldn't jump like that!
 
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