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Thread: LPG Backfire

  1. 17th August 2012, 02:27 PM #1
    ginger Guest

    LPG Backfire

    Hi Guys , I have followed the forum for years and found it to be a great help .
    I have a 1998 3.9 v8 done 120,000k's . I fitted a second hand Impco manifold injection LPG unit a couple of years ago and I am slowly ( with the help of the forum ) ironing out the bugs . I have put in the Bee Utey recommended plugs , changed the timing , new top gun leads and a new dizzy cap and rotor . I still had an annoying miss which I tracked down to the plenium not beeing sealed correctly and sucking in air ! .Now my final issue is I have an occasional backfire happening in the headers or upper exhaust . Seems to happen when decelerating when the engine is warm . Any ideas ?
    Thanks
    Ginger
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  2. 17th August 2012, 06:31 PM #2
    bee utey's Avatar
    bee utey
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    Backfires in the exhaust on over run are usually caused by exhaust leaks, generally around gaskets or slip joints. In petrol injection vehicles the injectors usually cut off completely on decel, if you have sequential gas injection it usually follows the petrol. This usually prevents these noises.

    On the other hand if you have a typical Impco mixer they deliver plenty of gas on decel to cause continuous banging in a leaky exhaust.
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  3. 24th August 2012, 05:25 PM #3
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    landrover dave
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    lpg

    Is it a backfire or just a 'pop' in the exhaust? If it is a pop in the exhaust this is usually caused by air being sucked into the exhaust system, or ignition timing. Have you had your distributor advance curve changed for gas? And what is your timing? It should be around 10-12deg btdc with the vac advance removed.



    Quote Originally Posted by ginger View Post
    Hi Guys , I have followed the forum for years and found it to be a great help .
    I have a 1998 3.9 v8 done 120,000k's . I fitted a second hand Impco manifold injection LPG unit a couple of years ago and I am slowly ( with the help of the forum ) ironing out the bugs . I have put in the Bee Utey recommended plugs , changed the timing , new top gun leads and a new dizzy cap and rotor . I still had an annoying miss which I tracked down to the plenium not beeing sealed correctly and sucking in air ! .Now my final issue is I have an occasional backfire happening in the headers or upper exhaust . Seems to happen when decelerating when the engine is warm . Any ideas ?
    Thanks
    Ginger
    Reply With Quote Reply With Quote
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