1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Symptoms of a blocked cat

Discussion in 'A4/S4 forum(B5 Chassis)' started by voteforpedro, Apr 7, 2010.

  1. voteforpedro
    Offline

    voteforpedro Member

    Joined:
    Jul 15, 2008
    Messages:
    632
    Likes Received:
    0
    I think my cat has had it. I drove it for 30 minutes yesterday and the engine bay was searing hot and I could smell burning. :(

    Something isn't right and I can't seem to diagnose it. It lacks pull, rough idle and crazy heat in engine bay.

    How can I tell fo sho that my cat is fooked? How difficult is it to replace? Those 3 cat>dp bolts are a PITA to get to but luckily they were replaced recently when I had my exhaust fitted...
    #1
  2. voteforpedro
    Offline

    voteforpedro Member

    Joined:
    Jul 15, 2008
    Messages:
    632
    Likes Received:
    0
    If I went down the decat route, is it a definite MOT failure?
    #2
  3. aragorn
    Online

    aragorn "Stick a V8 in it!" Staff Member Moderator

    Joined:
    Jan 30, 2008
    Messages:
    15,541
    Likes Received:
    303
    the turbo often starts glowing red with a blocked cat and there would be very little power at all.

    No cat is almost certainly an MOT failure.
    #3
  4. voteforpedro
    Offline

    voteforpedro Member

    Joined:
    Jul 15, 2008
    Messages:
    632
    Likes Received:
    0
    I've been told that if I had a blocked cat "I would know about it". Do you think I'm just being paranoid and should look elsewhere for faults?

    Thanks for the reassurance. :p
    #4
  5. aragorn
    Online

    aragorn "Stick a V8 in it!" Staff Member Moderator

    Joined:
    Jan 30, 2008
    Messages:
    15,541
    Likes Received:
    303
    When it happened to my dads 1.8T, you could barely get it to 60mph, so ye i think you'd know about it!
    #5
  6. jo
    Offline

    jo New Member

    Joined:
    Mar 31, 2010
    Messages:
    14
    Likes Received:
    0
    you have to have a cat on a car registered after 1991 for the mot, diesels on the other hand you dont.Nice one.:bye:
    #6
  7. Raveydavey
    Offline

    Raveydavey New Member

    Joined:
    Nov 29, 2009
    Messages:
    8
    Likes Received:
    0
    I had a completely blocked cat on my 2.5 and driving gently it seemed ok but put your foot down and nothing would happen. It wouldn't rev over 3k in 3rd, 2 1/2K in 4th and 2K in 5th and 6th.

    If you can get someone to cut the side of the cat and remove some without doing a load of diagnostic checks it costs an hours labour.

    Made the wrld of difference to mine. Goes like stink now. Sorry can't comment on the turbo/engine bay signs tho.
    #7
  8. aragorn
    Online

    aragorn "Stick a V8 in it!" Staff Member Moderator

    Joined:
    Jan 30, 2008
    Messages:
    15,541
    Likes Received:
    303
    Ye dads 1.8T was the same, if you VERY gently accellerated, it would pick up to 60ish, but if you tried to open up the throttle it would just bog down and cough/splutter and go nowhere.

    Simplest thing to do is unbolt the lambda sensor and take it for a drive.

    If it now goes properly, the cats at fault.
    #8
  9. voteforpedro
    Offline

    voteforpedro Member

    Joined:
    Jul 15, 2008
    Messages:
    632
    Likes Received:
    0
    Well I can drive it to the redline happily in first and second so I guess it's OK.

    How do you explain the excessive heat and smell coming from turbo/cat? Or is this normal?
    #9
  10. aragorn
    Online

    aragorn "Stick a V8 in it!" Staff Member Moderator

    Joined:
    Jan 30, 2008
    Messages:
    15,541
    Likes Received:
    303
    is the turbo glowing?

    The Turbo itself does get extremely hot and the cat will retain a lot of heat too.

    Have you had a scan for fault codes? Will it pull thru the revs in third or fourth?

    I'm just wondering if its wastegate failure, You notice it less in low gears... whereas in 3rd-5th it makes the car feel like a gutless 1.6. Have you had any rattling from the turbo, and if you roll the window down and drive along can you hear the turbo whistle?
    #10
  11. voteforpedro
    Offline

    voteforpedro Member

    Joined:
    Jul 15, 2008
    Messages:
    632
    Likes Received:
    0
    No glowing turbo, just very hot around that area. Haven't scanned for codes yet, will do on weekend.

    Haven't noticed any rattling either and it pulls good in first and second but does pull a bit **** in higher gears. When on the motorway, it certainly doesn't pull in 5th when I go to overtake like it used to.

    It's definitely boosting in low gears and I can hear the turbo but can't really hear it in higher gears, although road noise is louder too.

    I may fit my boost gauge at last on the weekend. Hopefully I can draw a conclusion from that. :)
    #11
  12. aragorn
    Online

    aragorn "Stick a V8 in it!" Staff Member Moderator

    Joined:
    Jan 30, 2008
    Messages:
    15,541
    Likes Received:
    303
    You need to get vagcom on and see whats happening
    #12

Share This Page