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Thread: Backfire!

  1. #1

    Default Backfire!

    The MSM is now regularly backfiring on the 1-2 upshift under full throttle. Happens every 40th time or so, a small pop from the exhaust. Couldn't figure out what the noise was at first -- it isn't very loud -- but I have now determined that it's either a backfire or else someone is hiding in my trunk and shooting a gun.

    Any cause for concern here?

    S.

  2. #2
    Team Cheap Bastard
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    sammm's Avatar
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    NC
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    Is it running rich? Any sign of black/soot around the tail pipe?

  3. #3

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    is it a factory exhaust? i friend of mines car will pop like that between shifts as well.

  4. #4

    Default

    Quote Originally Posted by sammm
    Is it running rich? Any sign of black/soot around the tail pipe?
    Not much. Certainly not more than I've had in any other car. Certainly, some gases aren't fully combusting in the engine, but I don't know whether this is cause for concern. I do want to answer this question before I install the FM downpipe.

    Yes, it's the factory exhaust.

    S.

  5. #5

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    How many miles? Have you checked the gap on the plugs? Is the air filter clean?

    RJ
    Daily Driver: 2013 Club edition in Pearl White Mica

    Lightness? What's that? I drive a PRHT!

  6. #6

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    5,000 miles. Can't imagine it's the plugs. I did drop a K&N filter in a while back. Hmm....

    S.

  7. #7

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    My 87 camaro used to backfire like crazy, but the timing was off.
    "Racing makes heroin addiction look like a vague longing for something salty" - Peter Egan

  8. #8

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    Quote Originally Posted by srivendel
    5,000 miles. Can't imagine it's the plugs. I did drop a K&N filter in a while back. Hmm....

    S.

    Lemme guess... you're shifting right about 5k?

    Mine does that too... the a/f goes WAY rich right there as teh boost kicks in. If you let off and shift before winding it out a ways you can get a backfire. Mie got worse with the FM DP.

    Its' pretty easy to replicate if I want to.. also easy enough to avoid...
    1984 GSL-SE - Its ALIVE!
    1989 Suburban 4x4 - 4" Pro-Comp Lift 33" BFGs etc... DRUNK TANK!
    2002 Protege5 - Lucky the drunk wagon SOLD
    '04 MazdaSpeed Mx-5 Wheeee! Turbos are fun
    How can I be so thirsty this morning, When I drank so much last night??

  9. #9

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    Quote Originally Posted by rx7gslse
    Lemme guess... you're shifting right about 5k?

    Mine does that too... the a/f goes WAY rich right there as teh boost kicks in. If you let off and shift before winding it out a ways you can get a backfire. Mie got worse with the FM DP.

    Its' pretty easy to replicate if I want to.. also easy enough to avoid...
    My '02 does the same thing... 3/4 throttle or more, shift between 4500 & 5500, POP!
    Maybe 4 wheels aren't so bad after all... wickett.org
    It only goes to show when people can no longer discriminate on the grounds of race, religion, or sexual orientation, they can improvise and still find someone to hate. - Dave Moulton

  10. #10

    Default

    Quote Originally Posted by rx7gslse
    Lemme guess... you're shifting right about 5k?

    Mine does that too... the a/f goes WAY rich right there as teh boost kicks in. If you let off and shift before winding it out a ways you can get a backfire. Mie got worse with the FM DP.

    Its' pretty easy to replicate if I want to.. also easy enough to avoid...
    Ding ding ding! We have a winner.

    Glad to know I'm not alone. Interesting that it got worse with the DP. I admit: it does make me feel pretty ricey (in a bad way).

    S.

  11. #11

    Default

    Quote Originally Posted by srivendel
    Ding ding ding! We have a winner.

    Glad to know I'm not alone. Interesting that it got worse with the DP. I admit: it does make me feel pretty ricey (in a bad way).

    S.

    I dunno if it really got worse, or if it just got louder with the elimination of a silencer... Eitherway, I noticed it more :)

    But yeah.. I've got the wideband gauge in teh car, and you can just see it pegg teh needle at about 4.5-5k rpm for anything under positive boost pressure. Drops right down below 11:1
    1984 GSL-SE - Its ALIVE!
    1989 Suburban 4x4 - 4" Pro-Comp Lift 33" BFGs etc... DRUNK TANK!
    2002 Protege5 - Lucky the drunk wagon SOLD
    '04 MazdaSpeed Mx-5 Wheeee! Turbos are fun
    How can I be so thirsty this morning, When I drank so much last night??

  12. #12

    Default

    would na's have a small series of backfires? i have a borla and TP. and i get it sometimes. doesnt bother me though. just wondering if that was it.
    -AJ Ngo

  13. #13
    Chassis Designer
    Join Date
    Jun 2005
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    Granbury Tx
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    My car used to backfire every once in a while in between full throttle shifts.. That was before I went FI and I had no cat so.. im guessing thats why
    1990 Red Turbo, Granbury TX..

  14. #14

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    if you have a turbo car with a bov vented to atmosphere it will backfire, and if you shift at the rev limiter with no muffler it will shoot out a flame
    Last edited by homerneedspeed; 10-11-2005 at 10:14 PM.

  15. #15

    Default

    My FM turbo pops a lot. I LIKE IT!
    93 FMII + LOTS MORE
    The Black Mamba

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