Question about Mercedes-Benz C-Class

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I have MB C240. There is some igniton failure in the 6 th cylinder. The spark plugs in the 6th cylinder are black and the engine is running like a dog with 3 legs. I tried a new ignition coil, but didn't get better result. What's the problem?

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  • pjpasanen Jan 01, 2011

    Hi there!

    Now I noticed that in the 6th cylinder the other spark plug (a) doesn't work with new ignition coil. I tested with an other one and a new plug wire, too, but didn't get better result.

    I think that the ignition coil doesn't get any current? What could be the solution now?

    - Pekka



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The chemical reaction inside the combustion camber will leave deposits on the spark plug that can tell you the condition inside the engine's combustion chambers. For example: if the engine is running rich all of the spark plugs will have a black or grey soot covering the spark plug electrode. If the engine is running lean all of the spark plugs will be clean and white (check your spark plug condition). If one of the spark plugs looks considerably different from the remaining spark plugs that cylinder might be having a problem. Before you remove the spark plugs, mark the plug wires to identify their positions in the firing order, this will help to make sure they do not get mixed up. The spark plug socket is lined with rubber to help cushion the spark plug insulator, which is made of porcelain and gets easily cracked or broken. If a spark plug insulator is cracked or broken the engine will misfire because the ignition spark will travel to the engine block (ground) instead of the spark plug gap (between the electrodes).In this case the spark plugs needs to be replaced. Also Sounds like a bad injector in cyl. # 6.Black sooty plug = too much fuel in that cylinder, causing the plug to foul. But if these parts are new are already replaced. Then other problem can be fuel pressure regulator. Get your cars fuel pressure checked. In most cases if all other parts are checked ok then fuel pressure will show low. In that case get the fuel pressure regulator replaced. This is letting more fuel then required to cylinder number 6 so it's getting black. But check all the possibilities before going to check fuel pressure. The possibilities like, worn out spark plug, bad injector, coil not fitted properly.----------------This will help.Thanks.Helpmech.

Posted on Dec 29, 2010

  • raj somaiya Jan 01, 2011

    A failed ignition coil can be the result of failures elsewhere in the ignition system. The ignition wires and spark plugs should be inspected and replaced if necessary.


    Oil or coolant leaks can damage ignition coils-the leaks need to be repaired along with the ignition coil.Failing ignition coils can cause the engine to run roughly or a lack of power upon acceleration.The Check Engine Light will often flash when the engine is misfiring-continuing to drive under these conditions can damage the catalytic converter.


    There are many other possibilities to be checked like,O2 sensor.crankshaft sensor,Maf sensor, Catalytic converter.the procedure of ignition coil working is as follows:---

    EN-US;mso-bidi-language:AR-SA">Mercedes Benz c-240
    AR-SA">uses one coil and two spark plugs per cylinder.
    EN-US;mso-bidi-language:AR-SA;text-decoration:none;text-underline:none"> On mso-fareast-language:EN-US;mso-bidi-language:AR-SA">C240 there is one coil
    located on the top of spark plugs and has a companion wire to the second spark
    mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language:AR-SA"> mso-fareast-language:EN-US;mso-bidi-language:AR-SA">The computer uses the
    crankshaft sensor for rpm determination and for position of the crankshaft
    relative to top dead center on the number 1 cylinder. It uses the mass air flow
    sensor and intake air temperature sensors for calculation of altitude above sea
    level in terms of air density. One oxygen sensor is in front of the catalytic
    converter, and the other is behind the catalytic converter. These sensors
    measure the amount of free oxygen in the exhaust system. All of these signals
    are used by the computer to determine the fuel-air ratio and the ignition
    timing necessary to burn as much of the fuel as possible. The computer uses
    these signals to tell the ignition module which coil to fire and when to fire.--------
    mso-bidi-font-family:Arial;color:black;border:none windowtext 1.0pt;mso-border-alt:
    none windowtext 0in;padding:0in;mso-ansi-language:EN-US;mso-fareast-language:
    EN-US;mso-bidi-language:AR-SA">But if ignition coil is new then it can be the problem with spark plugs. But if
    spark plugs checked out ok then the car Ignition Control Module is to be checked--------The module is faulty,so the new ignition coil is not getting power .----------------- This should help.Thanks.Helpmech.

    mso-bidi-font-family:Arial;color:black;border:none windowtext 1.0pt;mso-border-alt:
    none windowtext 0in;padding:0in;mso-ansi-language:EN-US;mso-fareast-language:



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