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308 now backfires-never did before

Discussion in 'Technical Q&A' started by Chiaroman, Jul 27, 2008.

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  1. Chiaroman

    Chiaroman Formula 3
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    Apr 21, 2004
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    New Jersey
    #1 Chiaroman, Jul 27, 2008
    Hello all,

    In March bottomed out and needed new belly pan, some straightening and broke transmission fluid cover.
    Get the car back in July and now it back fires. NEVER did in the six years I owned it.
    I am confused and concerned about why now?!?!

    Crack in exhaust system?
    Something jostled up in the air intake??
    From sitting for months?? (Did the Italian tune-up, and it's a little better)
    Need a real tune up? (I get one every year in October)
    Timing knocked off?? (No more points, went electronic)
    Doesn't do it much when at idle, mostly at the "bottom" or "start" of a gear when pulling.
    Sometimes it's a high pitch "ting" and sometimes a loud, deeper "pop".
    No loss of power. (Can still "chirp" third gear!!!)

    Any help will be greatly appreciated.

    Thanking all of you in advance,

    Yours,

    Tom
     
  2. Peter

    Peter F1 Veteran
    Owner

    Dec 21, 2000
    6,441
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    #2 Peter, Jul 28, 2008
    That could be part of the problem. Only way to find out is to drive until almost empty and fill up with a fresh tank of gas.

    You may be experiencing some kind-of lean mixture at that instance. Although why it should be leaning out only then?...

    Does it backfire on the overrun too? If it does, that is more than likely an exhaust leak, probably at the manifold-to-muffler flanges, (or worse, a crack somewhere along the manifold).
     
  3. thecarreaper

    thecarreaper F1 World Champ
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    #3 thecarreaper, Jul 29, 2008
    i vote for air leak in exhaust too.
     
  4. EMI-SC

    EMI-SC Karting

    Aug 2, 2008
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    Full Name:
    Chris Felber
    #4 EMI-SC, Aug 2, 2008

    X3
     
  5. Artvonne

    Artvonne F1 Veteran

    Oct 29, 2004
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    Paul
    #5 Artvonne, Aug 3, 2008
    X4. Plus its a lot easier to rule out than anything fuel or electrical/ignition related. Always start with the simplest and work your way down.
     
  6. Chiaroman

    Chiaroman Formula 3
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    #6 Chiaroman, Aug 12, 2008
    Sorry it took so long to get back but life got in the way...

    How does one actually look, listen for air in the exhaust?

    You simply put it up on a lift and poke around?

    Stethoscope?

    Like looking for a gas leak in a pipe only backward...could you put a liquid soap on the pipe and look for suction??

    Any help is greatly appreciated.

    Yours,

    Tom
     
  7. thecarreaper

    thecarreaper F1 World Champ
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    #7 thecarreaper, Aug 12, 2008
    i mean no disrespect, but it may be best to save you time and energy to take it to a shop and have them do an inspection of the exhaust on a lift. i will sometimes have someone inside and start the car and let it run while i am under it, and look for the leaks. pin holes the size of pencil lead will allow enough air in to cause the backfire, and if the holes are too close to the exhaust valves, the cold air will allow the valve to burn, damaging it.

    it could be the smog test lines, cracks in the manifold, cracks in the welds, rust holes, damage from hitting something in the road, it takes some time to throughly inspect even a short Ferrari system.
     
  8. Chiaroman

    Chiaroman Formula 3
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    #8 Chiaroman, Aug 12, 2008
    Thank you for your prompt very informative reply.


    Tom
     
  9. Chiaroman

    Chiaroman Formula 3
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    #9 Chiaroman, Aug 13, 2008
    Sorry for the caps but can't help but be excited to get the car purring again.

    The source of the backfire?!?!?!?

    A cracked spark plug!!!!

    Plugs changed and all is well!!!

    Thanks again for all your help!!

    Tom
     
  10. Peter

    Peter F1 Veteran
    Owner

    Dec 21, 2000
    6,441
    B.C., Canada
    #10 Peter, Aug 14, 2008
    Wow, that's something I wouldn't have thought of, because I've never encountered a problem like that...

    I suppose the porcelain part of the plug was cracked?

    Did the extender and spark plug wire dust boot get burnt, from the heat escaping the combustion chamber?
     

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