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  • Black smoke

    Hello guys. I sometimes have a problem with starting the engine. It starts for 4-5 seconds and then runs at very low revs for a few seconds. I add gas and black smoke comes out of the exhaust. Tried another lambda, same. The MAF sensor is about 50 tkm old. I measured the voltages on it and they are within the specified values. Engine temperature sensor in tolerance. A warm engine does not smoke. The engine does not consume oil or water. It works nicely. It's going really well. Do you have any ideas? Thanks

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  • #2
    How does it start when it's hot?
    Have you go any fault codes?
    Nothelle S2 Avant
    Black Ur project
    Ocianic Ur project gone
    S2 Coupe project gone
    Urs6 plus project gone

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    • #3
      No fault codes. The car starts the worst 2-3 hours after driving. Warm starts well. Cold mostly good but not always.

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      • #4
        I'm sure you know black smoke indicates rich mixture. Could be a number of things. You might have a leaky injector. All all the spark plugs the same or is just one black?
        Nothelle S2 Avant
        Black Ur project
        Ocianic Ur project gone
        S2 Coupe project gone
        Urs6 plus project gone

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        • #5
          Good idea. I checked the fuel pressure yesterday. 4 bars constantly. After 3 hours of standing, the pressure dropped to 1 bar. I have had the car for 10 years. I removed the hose from the rail several times. Otherwise, 1 dl of gasoline leaks out and that's it. However, when I took it off yesterday I was shocked. Half a liter of gasoline under pressure leaked out of the hose. the gasoline was warm, I guess from the engine compartment.
          This happened before the pressure gauge was installed so I don't know the pressure.

          Is it normal for that much pressure to be in the fuel hoses?
          Who controls the pressure in the fuel tank while the engine is off?

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          • #6
            You normally get quite a squirt of fuel when disconnecting any of the supply unions, there is a non return valve fitted to the top of some pump's on S2 Coupe, I binned mine when fitting an 044 as I needed the extra head room.

            It made no difference to the amount of fuel that went everywhere when undoing a union so I guess the pump itself hold a certain amount of pressure.

            Black smoke is always un-burnt fuel.

            That Lambda does look a touch black.
            1989 B3 2.0 3A 80 quattro... Budget 1.8T Project.
            1992 C4 100 2.8 Avant quattro... Mobile Sitting Room.
            1995 RS2... MTM K26/7 380 BHP Conversion.
            1990 Corrado G60... Breaking For Parts.

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