cold start low rpm rattle noise - cat?

Discussion in '2005+ Mustang GT 4.6L Tech' started by tabstang, Jan 3, 2021.

  1. tabstang

    tabstang Junior Member

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    I recently got a terrible metallic rattle noise that goes away at higher rpm, and declines with rising engine temp. I went through the exhaust with a rubber mallet and everything seemed tight. The sound seems to be from the passenger side cat. I'm surprised how loud it is.

    Is there a way to test for a bad cat? I haven't gotten any computer warnings.
     
  2. Laga

    Laga Member

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    When you tested the exhaust, did you check for loose heat shields also?
     
  3. tabstang

    tabstang Junior Member

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    yes, the passenger side one vibrated a bit but I bent it a little and the vibe stopped. The sound is so loud I thought I had dropped something on top of the heat shield - but didn't find anything loose. I'll go back check the mounting bolts also
     
  4. Laga

    Laga Member

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    If your cat is bad enough to rattle, you should hear the rattle with the mallet. Then check the hangers. I had one hanger that would rattle only when hot. Intermittent problems are the worst.
     
  5. tabstang

    tabstang Junior Member

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    thanks for the insight - I have worked on the exhaust (replaced muffler hanger bolts) fairly recently, I'll check the whole system sometime soon and report any findings.
     
  6. ShelbySteve

    ShelbySteve Member

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    I had heat shields rattling and ended up with 2 busted cats about a week apart (my car had less than 20k miles put on it in 12 years). My busted cats sounded like someone put ball bearings in the exhaust it rattled so bad. The guy at the exhaust shop tapped each cat with the hammer handle and you could hear which one was bad.
     
  7. Laga

    Laga Member

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    After installing a cat back system, I adjusted the tubes so the exhaust tips were centered in the openings. One hanger was slightly off. It only rattled when hot and things expanded and moved. The weight was carried by the other hangers and this one was touching but basically loose. Instead of tearing everything apart to try to bend hanger, I filled the inside of the rubber mount where the hanger rod goes with HD silicone. Three years later, still no rattle.
     
  8. 06monera96

    06monera96 LeShawno

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    I had the same issue...
    let's just say I lost the motor
    Timing chain bouncing off the cover,
    Collapse tensioner and guide had broke
     
  9. JeremyH

    JeremyH 3V Fuel Guru S197 Team Member

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    Sounds like textvook bellhousing separator plate buzz/rattle tsb. So check that too.
     
  10. tabstang

    tabstang Junior Member

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    Problem solved! it was the cat, the media was in pieces. (I thought I had already responded to this, not sure what happened.) So now I have my long tubes / mini-cats in - wow, big low end torque improvement, sounds freakin awessome! But what a PITA installing those headers!
     
    bmeaggie and ShelbySteve like this.
  11. Juice

    Juice forum member

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    Did you have to get a tune?
    Im about to do the same, and have been researching LT tuning. Some claim tuning not needed, and some do change transport delay.
     
  12. tabstang

    tabstang Junior Member

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    Kinda hard to say... on the FIRST TEST DRIVE I HIT A HERD OF DEER! So it's garaged for now but it seemed OK. I've been experiencing some throttle tip-in hesitation and then surging at lower rpms but that was already there b4 the long tubes.
     
  13. Laga

    Laga Member

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    Get the tune!!!
     
  14. Juice

    Juice forum member

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    Psss, I have the SCT software. I just need to make a new tune, if needed. I will more than likely run with no change at first, than test the long tube tweaks to see if I can feel any difference.
     
  15. bmeaggie

    bmeaggie Junior Member

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    This is how I justify the lawlessness of going catless... two less things to fail, lol!
     
  16. Juice

    Juice forum member

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    Till you get spot checked or need to pass visual inspection for emissions testing....
     
  17. bmeaggie

    bmeaggie Junior Member

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    I must be crazy... I also run with scissors!
     
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