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Thread: LPG. Missfiring, rough idle and rough running.

  1. #11
    Advanced Ryanbaxwar's Avatar
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    having a ruff idle issue with mine, trouble is i have no idea how the gas systems work at all, this is my first car on lpg and i hate to say it but i think im going to have to take it to a mechanic and have them figure it out cause iv tried all the things i would if it was on dedicated ulp

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  3. #12
    Grumpz mudnut's Avatar
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    Is it idling rough on both fuels?
    "I am entitled to my own opinion, but the world seems to have forgotten that." E.W.

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    thanks for the tips guys!

  5. #14
    Grumpz mudnut's Avatar
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    I was chatting with a gas specialist about valve recession on dual fuel and straight gas engines. His take on it was there is a myth the running LPG rich will lower the burn temp. In actual fact it will cause the mixture to still be burning as it exits the exhaust port. This will raise the temperature of the valve and seat, causing wear.
    Now, whether this is true, or not is open to debate.

    I was under the impression that since LPG is a dry fuel, there is no additive which will coat the valve and seat so they will suffer abnormal wear.

    Yet another mechanic I talked with, dislikes the valve lube systems as in his experience they 'gum up the works'.

    I would love to get to the truth of the matter, as I have come into possession of on old dual fuel Falcon.
    Last edited by mudnut; 17th April 2017 at 12:52 AM.
    "I am entitled to my own opinion, but the world seems to have forgotten that." E.W.

  6. #15
    Legendary dom14's Avatar
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    Quote Originally Posted by mudnut View Post
    I was chatting with a gas specialist about valve recession on dual fuel and straight gas engines. His take on it was there is a myth the running LPG rich will lower the burn temp. In actual fact it will cause the mixture to still be burning as it exits the exhaust port. This will raise the temperature of the valve and seat, causing wear.
    Now, whether this is true, or not is open to debate.
    Well...if the rich LPG mixture still burns as it exits the exhaust valve/port, then the same thing should be true for petrol as well.

    I was under the impression that since LPG is a dry fuel, there is no additive which will coat the valve and seat so they will suffer abnormal wear.

    Yet another mechanic I talked with, dislikes the valve lube systems as in his experience they 'gum up the works'.
    Unless petrol/air mixture is super rich, petrol/air mixture also should enter the combustion chamber as a "dry" mixture.

    Since LPG vapour enters the combustion chamber as a gas, it's generally lower in temperature than petrol vapour.
    I'm not sure whether that is an advantage or disadvantage, in general.

    I think it all comes down to how the ignition system is tweaked and tuned for LPG.

    The real issue is dual fuel system. If it's an EFI system, a unique ignition curve should be programmed into the ECU in the form of an added chip or something, or if it's a carby, a dual curve unit should be installed. Neither one of those things usually happens with many dual fuel systems, hence the reason for all the dramas, including engine failures.

    It is my belief, a properly tweaked and tuned LPG engine(not a dual fuel one) can outlast a petrol engine.

    I would love to get to the truth of the matter, as I have come into possession of on old dual fuel Falcon.
    Hold on to your wallet pretty tight with that troll.
    Start collecting spare parts, if you're intending to keep the Falcon.
    Buying another identical falcon and keeping it in the backyard might be a good idea.
    Last edited by dom14; 21st April 2017 at 11:19 PM.
    RB30, some 2-3 inch lift auxiliary LPG tanks
    Few more mods on the way
    http://www.worldwildlife.org/species/tiger
    https://www.panthera.org/
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  7. #16
    Patrol God threedogs's Avatar
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    Not sure thats true saying gas vapour is colder than petrol vapours.
    Ive melted many a carbie from running my gas too lean,
    04 ST 3lt auto, not enough Mods to keep me happy, but getting there

  8. #17
    Legendary dom14's Avatar
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    Quote Originally Posted by threedogs View Post
    Not sure thats true saying gas vapour is colder than petrol vapours.
    Ive melted many a carbie from running my gas too lean,
    May be from 45 magnum power backfires?

    In my RB30, the directional cup thingy under the carby base plate was broken into pieces.
    I had a good feeling it was from heavy backfires.
    What I don't understand is that how the Impco 300A mixer diaphragms managed to survive those strong backfires!!!
    RB30, some 2-3 inch lift auxiliary LPG tanks
    Few more mods on the way
    http://www.worldwildlife.org/species/tiger
    https://www.panthera.org/
    Cheetah Outreach

  9. #18
    Legendary dom14's Avatar
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    Quote Originally Posted by mudnut View Post
    I was under the impression that since LPG is a dry fuel, there is no additive which will coat the valve and seat so they will suffer abnormal wear.

    Yet another mechanic I talked with, dislikes the valve lube systems as in his experience they 'gum up the works'.
    I've heard some guys who know a bit about LPG vehicles saying the upper cylinder lube is a bit of a scam.(not my words).
    RB30, some 2-3 inch lift auxiliary LPG tanks
    Few more mods on the way
    http://www.worldwildlife.org/species/tiger
    https://www.panthera.org/
    Cheetah Outreach

  10. The Following User Says Thank You to dom14 For This Useful Post:

    mudnut (25th April 2017)

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