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S class 2.8 misfire

Discussion in 'Electrics, Vacuum, Ignition and ECU' started by 380560, Jan 6, 2013.

  1. 380560

    380560 Senior Member

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    Joined:
    Jul 22, 2008
    Location:
    Isle of Skye Highlands
    Your Mercedes:
    S Class, W140 4.2 Limo, Nissan 300ZX twin turbo, Porsche 911.
    Hi everyone hope you all had a great Christmas and new year. I know I have started a new thread on basically the same problem, the misfire on my 2.8 S class, but I still have the same problem with it. I have had a quick look at the ignition coils which sit on top of the engine and closer inspections show that there appears to be bear wires on the THINNER cable opposite the thicker (HT?) cable fitted to the centre coil, could this be the cause of the misfire? I obviously want to replace it but not sure what it is or what it is called to enable me to order one correctly! Just a reminder, the car has covered only 69,000 miles and is an L reg. Oh, also the cover which covers the coils is missing and has been since I bought the car about 4 months ago. Possibly this misfire has happened before, is it recommended to replace and fit a new cover or does the cover keep moisture/ damp in if fitted? Thanks
     
  2. OP
    380560

    380560 Senior Member

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    Joined:
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    Location:
    Isle of Skye Highlands
    Your Mercedes:
    S Class, W140 4.2 Limo, Nissan 300ZX twin turbo, Porsche 911.
    hello, any help ref my issue please
     
  3. Uncle Benz

    Uncle Benz Senior Member

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    Your Mercedes:
    Mainly Mercedes
    I mentioned in the other thread you started on the same topic to look for broken down insulation on the coil wiring. It sounds like that is what you have found. If left, shorting out here can severely damage the ecu. I would say get that fixed first and see how you go.
     
  4. Bolide

    Bolide Senior Member

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    Your Mercedes:
    BMW 525 Diesel Touring
    MB supply a loom repair section for £7 per coil which consists of a coil plug plus about 3 metres of cable. Cut into the loom and trace the three coil feeds back towards the ECU. Lay in the three new sections, cut them to length and solder them to the feeds from the ECU at an appropriate point in the loom - I suggest the straight section close to the second bulkhead. From memory the inner of the new coil plug is blue and the outer brown but check the polarity of the existing cabling and follow it

    Before you start cutting into the loom be aware that it can all go horribly wrong with insulation dropping off every wire. I haven't had that but it wouldn't be the first time

    Nick Froome
     
  5. OP
    380560

    380560 Senior Member

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    Joined:
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    Location:
    Isle of Skye Highlands
    Your Mercedes:
    S Class, W140 4.2 Limo, Nissan 300ZX twin turbo, Porsche 911.
    Thanks for the replies. Today I fitted a new coil (centre), all appeared to be well until she warmed up and the misfire started again. Tonight, once dark, I started her up again and she started to misfire once warm again (no surprize there) I noted that there was a lot of blue spark activity going on at cylinder three plug cap and all a long the HT lead and also arking against the top of the engine I also noted that there was an occasional ark from the new coil I fitted. I assume its time for new HT leads?? but the leads do look in very good condition and possibly not long fitted.

    I don't know if this is effected by the ignition problem, buy yesterday the rear windscreen demist switch would not switck off and the little light in the switch was flickering bright then dim for about 10 mins??? Any ideas???
     
  6. kth286

    kth286 Senior Member

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    Your Mercedes:
    E320 Coupe 95
    my same engine (version 3.2 litre 104) has the same leads for 193,000 miles.

    just give them a wipe, unless the insulation has been punctured, then replace that one.

    I would think that the plugs on ends not been fitted properly when new leads put on your car.

    if purchased from Merc dealer they make them up in parts dept to individual requirements, while you wait.
     
  7. OP
    380560

    380560 Senior Member

    Messages:
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    Joined:
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    Location:
    Isle of Skye Highlands
    Your Mercedes:
    S Class, W140 4.2 Limo, Nissan 300ZX twin turbo, Porsche 911.
    The car was running fine up until last week, the leads although look quite new have been on the car before I bought it 5 months ago and approx 800 miles, not sure how long before I bought it. I will try what you say and see how it goes. Any idea why the rear demister should act the way I described above, is it contected?
    In an earlier thread I said that the ASD warning light has come on and only goes out when I press the brake pedal, any connection?
     

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