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Thread: cuore intermittent misfire

  1. #1
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    Default cuore intermittent misfire

    I have a problem of intermittent misfire in cuore -06 both on cng and petrol. Below things I have already done
    - changed spark plugs
    - air filter
    - checked distributor point gap, it is at .45 mm ( The point is used over 20K kilometers but no visible wear)
    - cleaned distributor cover and rotor

    The above things did improve the performance but the random missing is still there.

    I also checked the spark plug wires resistance , from shortest to longest each one was showing 7.5 K ohms, 8K ohms and 9.5 K Ohms. This is within the factory manual specified range of maximum 15K ohms.

    Also checked the ignition coil primary resistance it was 2.5 ohms , The factory manual says it should be between 1.35 to 1.65 ohms. My reading is slightly out of this range but I am uncertain since ignition coils dont go bad so soon.

    What could be possible problem here??


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    hmm i had the same problem...car was totally not performing the way it should... thanks to Toyota Mechanics...... but i found a good tuner and he fixed it... gave it a regular tune up....cleaning the plugs, air filter, checked the tappets... and its been working just fine....
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    did this happen after using carb cleaner?
    haters gonna hate, potatoes gonna potate

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    @jiggerzzzz. I normally get it tuned by toyota 3s after 5K kilometers but this problem has been there since last two tune ups.

    @margallar . No this is an old problem, I actually tried carb cleaner hoping to fix this. The carb cleaner did slight improvement in idle rpm, not a huge difference

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    Default

    maybe the mixture is bad
    haters gonna hate, potatoes gonna potate

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    Default

    the missing is almost identical on petrol and cng, that's why i suspect its something other than mixture setting.
    btw I have one question can carburetor air mixture setting affect CNG also??

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    Default

    as much as i know, cng and petrol have different and independent settings
    haters gonna hate, potatoes gonna potate

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    Mixture for CNG & Petrol is independently adjusted, Margallar is right.

    the missing?? is it at certain RPM or randomly abrupt try the glow-in-dark diagnosis - need 2 people for that, after sunset park your car in dark corner turn off head lamps neutral your car, pull the parking break, if she is auto trans shift to P. start the engine carefully lift the hood watch look at the plug-side and at plug ht cables throttle randomly and see when it mis-fire may be you can figure out HT STREAK randomly from either of plug cable.

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    best way to check is to spray the cables with a mist of water from a spritz bottle - the current leak will show itself as an arc and possible engine shutdown.
    ZRS - Zulfiqar Racing Systems ..... - professionals at work - at crackwheels.com

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    ok I will check for current leakage.

    btw the misfiring is felt on idling, on high rpm while driving it feels there is lack of power

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    Set the point gap at 0.35 mm & see the result.Some times due to over tightness, insulating washer (Point ki haadi in local language) gets cracked and causing for current leakage which leads to no or insufficient spark in spark plugs.So also check this point ki haadi as well.
    Never loose hope in life,every step gives u something.

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    Best solution is use NGK BPR-GAS/LPG spark plugs pre gapped frm factory n wth bigger tip for CNG/lpg engines
    DIY The Best Workshop on the Holy Planet!
    Every thing changes,Its only the "change" which never changes.

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    Tried to search for a visible spark in dark but it was not there.

    Also adjusted point gap to 0.35 but this still did not fix the problem. I even replaced a new genuine daihatsu point but still the problem is there.

    Another thing I noticed that on CNG if i block air intake with hand then the engine stalls but on petrol if i block the intake with hand it keeps running at the same rpm...

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    Slightly retard the ignition timing and see the result.If it not works then replace the distributor cap and spark plug cables.
    Never loose hope in life,every step gives u something.

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    The main cause of back/misfire is advance timing. Set timing to the normal and compare the results.

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    Quote Originally Posted by argtr65 View Post
    Slightly retard the ignition timing and see the result.If it not works then replace the distributor cap and spark plug cables.
    Ok, tried a few things
    - re adjusted gas mixture
    - adjusted tappets clearance to .20 mm
    - slightly retarded timing

    now the misfiring pattern has changed to rough idling... what next ???

  17. #17
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    Since I have set all things to spec (tappets regapped, new point, genuine air filter, new plugs, carb cleaner sprays) I guess it narrows down to plug wires or vacuum leak. The car runs very well apart from missing beats on idling.
    Again the plug wires showed correct resistance on ohm-meter (measured from inside distributor cap to plug side ends). A New genuine sumitomo plug wire set costs slightly above 4K rupees so I would opt for it last . Distributor cap is also in fairly good condition.

    I took a quick inspection of vacum lines and nothing seemed unusual. Lastly I am left with the possibility of leaky fuel pump disturbing the vacuum. Read in some user's posts that these type of fuel pumps go faulty in a few years due to CNG cutover switch in the fuel line path. I am searching for ways to check if its faulty.

    Its one of those frustrating problems which has taken months and still unidentified. I did not want to change a part unless it is confirmed as defected.
    If I take to dealership they simply ask to do engine tuning again, so stayed away from them for now.
    Still searching ...

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    check the condenser and coil impedance too. You need to adjust the dwell back to 0.45mm clearance at point rub heel and cam (the fit should be easy slide not drag like the tappets)

    Do not use sandpaper or any abrasive to clean the distributor cap or rotor. It can create current leaks.
    ZRS - Zulfiqar Racing Systems ..... - professionals at work - at crackwheels.com

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    Quote Originally Posted by Xulfiqar View Post
    check the condenser and coil impedance too. You need to adjust the dwell back to 0.45mm clearance at point rub heel and cam (the fit should be easy slide not drag like the tappets)

    Do not use sandpaper or any abrasive to clean the distributor cap or rotor. It can create current leaks.
    Regarding condenser- I think the points would wear out very soon if condenser is at fault, but old points did not show any sign of wear, only the heel worn from rubbing on cam lobes

    Coil- Only managed to check primary resistance which seemed ok, will also check secondary size but the cable boot wont budge from secondary

    Point- Yes already regapped to 0.45

    What would correct procedure to clean the distributor caps?

    And I also got it inspected from a stealership (dealeship) , took Rs 100 only for inspection. Again their senior tech asked for re-tuning the engine from them and said the butterfly inside carburetor is faulty (he judged this without opening anything) and needs repair from Kharadia, quoted me Rs 3000 for butterfly repair.
    These charges seem too much? Any idea what would be justified charges for butterfly repair. And whether I really need it or not ???

    Also can I avoid opening up the carb by using carb cleaners (trying already and it improves idling for sometime) or driving on petrol for sometime??

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