Black smoke and fuel smell

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  • #1004119
    ilyes ferchiou
    ilyes ferchiou

    I have a Fiat Punto mk2 from 2004 that has a petroleum engine 1.2L 60HP.

    I have had an intermittent ignition coil problem where the car would start shaking when idle and when the engine is hot (when the fans start) for a brief moment and stops when I accelerate. The problem went unfixed for a month or two.

    Last week I changed the faulty ignition coil and changed the spark plugs at the same time.

    The same night I started smelling petroleum inside the car and from the tailpipe. I suspected loose sparks plugs so I removed them and found them fouled with carbon, I cleaned them, checked the gap again, put them back and made sure they are perfectly tight. But the problem remained.

    The next day, the car started producing black smoke but not very visible. When the engine is idle, it is smalls puffs of black smoke that happen at regular intervals (maybe every half a second or a second) and in between the exhaust is clear. When I accelerate, there is a big puff of smoke and then the smoke stops completely until the car idles again or until I decelerate a lot and accelerate again.

    When the car produces small puffs of black smoke, the engine “sputters” (is that the right word ?) at the same rate and then it seems like it wants to accelerate or stabilize and then it starts “sputtering” again but there are no loud noises or any alarming ones.

    I also noticed that the acceleration is not as smooth, the car is hard to accelerate, and sometimes, when idle, the rpm goes high and stays high until I press the gas pedal and than remove my foot (while being in neutral). Most of the time, the rpm returns to normal but rarely it won’t until I turn off and on the engine or until I drive for some distance.

    The car also threw a bad O2 sensor error code and although I had it changed 9 months ago, I went ahead and changed it again. When I removed the old one, it was fouled with a lot of carbon.

    After changing the O2 sensor, the smoke stopped for 2 days but the fuel smell remained. Now the black smoke is back again and there are no error codes at all.

    There is also a strong gas smell in the oil dip.

    Is it possible that the new spark plugs are faulty ? It also came to my mind that I haven’t changed the oil for 14 000 kilometers. Could this be the issue ? Honestly, I have no clue where to go from here, all I know is I have a rich fuel mixture and it could be anything but without codes it is so hard to diagnose. I’m even thinking the catalytic converter since the car has a mileage of about 200 000 kilometers.

    Any help would be appreciated.

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  • Author
  • #1004126
    EricTheCarGuy 1

    I would start with a compression test to make sure the engine is in good mechanical condition. If there is a compression loss it can cause issues like what you’re experiencing. If the compression is good, then I’d be looking at the fuel system. It seems to be running rich for some reason. It could be a leaking or malfunctioning fuel injector.

    More info on solving problems like this here:

    Good hunting and please keep us posted.

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