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when i start my car up in the morning it starts up with a loud, kind of a knocking then it goes away. This only happens when it cold.I was wondering could it be that i just had all three cats replaced with new ones because before they were replaced i didnt have this problem but i replaceed the engine also. I dont know what the problem is could someone help me out
 

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piston slap. when cold your pistons are too small, and bounce around in the cylinder. once it warms up, the pistons expand (due to heat) and the slap goes away.

Usually only forged engines have this problem, but some engines are known to have it stock.
 

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I actually had something similar back when I used Fram filters. I have now switched to Motorcraft filters and haven't had a problem with it since. You may want to look into it if youre using a Fram.
 

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I don't think it's piston slap. I notice it in my '95 cougar and in my in-laws '03 GT mustang right after I change the oil every time. It's something with the oil out of the engine. In your case sounds like your filter might be draining empty and your valve train (cams, lash adjusters and rockers) hammer each other when it's cold cause all the oil is completely in the pan. The lash adjusters need oil to work like a hydrolic lifter in a 5.0 or something. With no oil pressure they are soft then when the oil is finally pumped to them they harden and the noise goes away.

Hope this helps,

Clay

PS - doesn't sound serious to me, just don't rev it could and let it warm up for about 3-5 min before you drive it. Yeah, try a Motorcraft filter or get a new Motorcraft.
 

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How crazy, I just replaced my cats too and it's starting to sound dry on startup. I don't see how it could be the cats though. But I never noticed it before, unless it was right after I changed the oil.
 

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Its common on modulars..... best run them on Mobil 1, and let them idle, or drive verry easy for a bit till things get warm, and oiled....It is not a problem unssless you start out raceing evry morning
 

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mine does the same exact thing when its cold.
 

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So I think it's starting to affect it while I'm driving too. I didn't notice it until today when I was driving with the windows down, but I hear a distinct "metallic" sound coming from the engine. I let off the gas and it goes away. It's ever so slight that most people wouldn't even notice it. Think it could be from the same thing? It's been warm outside and it's still be "sounding dry" after startup (even after just 4 hours) for the past month.

So what do I do about it? If this was happening to your engine would you be worried? I've tried listening to the engine with a "stehescope" kinda thing, but it sounds like a healthly engine to me. Also, under WOT it sounds as healthly as could be.
 

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Discussion Starter #10
Missycougar I would be worryed about that sound and then I wouldnt because before i replaced my enginemy car was making that noise due to over heating but the gauge said that it was normal when it was not. So everytime i took off after the car warmed up it would make like a grinding or metallic noise then i blew a head. so you might ant to get that checked out FOR REAL. By any chance is yourcheck engine lite on or does your temp gauge go in the middle and also why did you have to replace your cats?
 

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My check engine light had been on for quite some time due to "Catalyst System Efficiency behold threshold", I had them flow tested and they were fine. So I replaced the whole y pipe assembly and got 4 new 02 sensors. That was about a month ago, and about 1000 miles. So far, no check engine light again.

As far as my temp gauge, I’ve never seen it above the middle. My low coolant light comes on very rarely and its just barley been low enough to make the light come on. It has only happened a few times after I replaced my upper radiator hose, so I figured I might have some air in there that is finally escaping. I dunno.
 

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I think I'm still going to have someone look at it, just for a second "in person" opinion. Better safe then sorry.
 

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I have good news, it's starting to sound like an exshaut leak. I took it somewhere and they weren't sure. I'll talk to someone else aobut the engine making the noise.
 

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I was going to say piston slap also. My '96 sat for a straight week in the coldest temperatures of the whole year and man did it ever slap. Was the only time I've ever heard it do that, and it has sat for many longer periods of time since then.
 

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When a engine is first started, there is no oil pressure. The knock you hear is parts grinding together until the oil pressure is normal. I have read in several places that 90% of engine wear occurs when the engine is cold started. The knock is even worse after the oil is changed since the oil filter is empty.

W.Cup
 

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W.Cup said:
When a engine is first started, there is no oil pressure. The knock you hear is parts grinding together until the oil pressure is normal. I have read in several places that 90% of engine wear occurs when the engine is cold started. The knock is even worse after the oil is changed since the oil filter is empty.

W.Cup

Of course there isn't any oil pressure when it's started, the reason that I'm worried, is it never used to do it almost everytime i would start the car.
 

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I had it all inspected yesterday and they couldn't find anything wrong with the install. This was by a another shop that didn't do the work. They thought it might be leaking where the y pipe meets the header on the passenger side. When I get time, I'll bring it back to where I got it done at and see what they say.
 
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