Have we got any old benz expetrts on here?

Discussion in 'Engine' started by popuptoaster, Oct 22, 2008.

  1. popuptoaster

    popuptoaster Hardcore MB Enthusiast

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    I'm having trouble finding out which ignition parts my 1975 280ce should have on it, according to the Mercedes parts computers and my VIN number my car shouldnt have a ballast resistor on it, although plainly it does have one, its a proper Bosche one but the part number on it doesn't match up to any of the resistors fitted to the w114s of which there are about 5 different ones, and as they average £25 i dont really want to order one at random and then melt it, i gotta sort the problem out as my car is killing ignition coils at the rate of one every 50 miles or so, which is not good as i want to fit genuine mercedes parts back on it rather than aftermarket ones and Merc coils are 50 quid each. :S

    it would be handy if i could find a complete list of the correct ignition parts that mine should be fitted with.
     
  2. vijilants

    vijilants Hardcore MB Enthusiast

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    Try the mercedes benz owners club....they should be able to help you out on this one as they generally tend to specialise in the older models:

    http://www.mercedes-benz-club.co.uk/


    Regarding your problem, maybe your car doesn't have the original ballast resistor fitted ? Can't understand as to why your coil is burning out soo quickly though. You don't need to go to Mercedes for the coil though as you can easily fit a Bosch one. (Unless MB are selling them cheaper)
     
    Last edited: Oct 22, 2008
  3. OP
    OP
    popuptoaster

    popuptoaster Hardcore MB Enthusiast

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  4. andy_k

    andy_k MB Club Veteran

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    we've got an "unmolested" '78 280E sat outside - if you want any specific pictures of the engine bay to identify parts - let me know and I'll nip out with the camera for you

    HTH

    Andy
     
  5. OP
    OP
    popuptoaster

    popuptoaster Hardcore MB Enthusiast

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    cheers, took some pics of mine, take no notice of the coil, its the wrong one but i was using it to test the old one was dead.

    This is the corner where the sparky stuff is
    [​IMG]

    this is the ballast resistor i have, tucked down under the coil
    [​IMG]

    you can see where the resistor is in relation to to coil here.
    [​IMG]


    irritatingly it seems that whatever coil you put on there from your old stash in the shed lasts about the same amount of time, i suspect that unless mercedes where making some odd coils back in the 70's that the balast resistor isnt dropping the voltage to the coil like it should and they are simply burning out, of course my testing has been limited to just fitting another coil when the car packs up and wont restart and seeing if it does then restart, which it has done everytime.
     
  6. vijilants

    vijilants Hardcore MB Enthusiast

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    You need a voltmeter to test this. Check the voltage on one end of the ballast resistor and then test it on the other end that faces the coil.

    Or else, you are right....things are going to get expensive.
     
  7. andy_k

    andy_k MB Club Veteran

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    I'll add some pics of ours in the morning when the light is a bit better (and when my other half has come home with the keys for it :))
     
  8. OP
    OP
    popuptoaster

    popuptoaster Hardcore MB Enthusiast

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    cant complain to much about prices really, mercedes want 30 quid for a dizzy cap while my local parts place want £60 although their coils are half the price of mercedes ones, odd but there ya go. :)
     
  9. grober

    grober MB Club Veteran

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    There are several things to check. Back to first principles.
    If your distributor has a condenser across the points it may be faulty leading to continuous current through the primary winding of the coil. I would change it anyway.The ballast resistor must be matched to the coil such that the voltage drop across the coil is correct e.g. 4.5volts across the ballast 7.5 across the coil. this voltage split ratio can vary so they must be matched. The starting supply to the coil is normally taken from a connection on the starter solenoid such that while the starter is operating direct battery voltage is supplied to the coil. Because of the large current draw of the starter motor the battery voltage is pulled down to say 8 volts thus the coil still sees the correct operating voltage while the starter turns This helps the car to start. As soon as the starter is disengaged the coil supply reverts to its normal supply via the ballast resistor from the ignition switch.
    The other thing to watch for is coil polarity older coils have terminals marked sw (switch/ignition) cb contact breaker different versions of these were produced for positive and negative earth cars. (does your car have positive or negative earth?) you may have to switch connections. Modern coils are marked +/- the +ve terminal is connected to the contact breaker lead for +ve earth and the -ve coil terminal to the contact breaker for neg earth systems.
    The only other thing I can think of is that some cars (french mainly)had a special semi-conductor ballast resistor which on ignition switch on had low resistance when cold but increased in resistance as current thro the coil warmed it up thus dropping voltage across the coil. this type does not require a second direct battery 12v via the starter solenoid obviously.

    As has been suggested best get a voltmeter out and get a feel for whats going on in the circuitry during 1. STARTING 2. RUNNING. Because the common factor is the ballast resistor I would try changing it also but matching it to the coil obviously.

    might also be worth contacting these guys? http://www.123ignition.nl/products.php
     
    Last edited: Oct 22, 2008
  10. supercharger

    supercharger Active Member

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    just been reading this link and it may be of no relevance, but about 4 years ago i had a problem with my supercharged w126 380sel. the symptoms where poor running especially at idle and after 50 to 80 miles death of the coil. the first time was entering the showground at tatton park car show in june (highly embarassing).i went through about 4 before an independent garage found the cause. a few months prior to the problem i had fitted a new set of perfromance ignition leads. and it seemed one of them was faulty it was arching and tracking back up the lead and killing the coil..
    as i said further up may be of no relevance but worth checking the leads. the best way is to run the car in the garage at night in total darkness have a good look round under the bonnet and see if you can see any arcing.

    supercharger
     
  11. OP
    OP
    popuptoaster

    popuptoaster Hardcore MB Enthusiast

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    cheers guys, i'll have to go get a meter (ran over mine, dont ask!) car runs perfect until the it develops a missfire, which gradually gets worse and worse until the car wont run at all.

    sounds like as long as the coil is matched to the ballast resistor it shouldnt matter which one of the 5 available ones i pick as long as i get all the ignition parts from the same "set"
     
  12. Rasputin

    Rasputin Member

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    Since 1985 Mercedes superseded the prior 0.4 and 0.9 Ohms by a 0.6 Ohms used in many models with ballast resistor. Earlier resistors were not completely encased (the back was open) and the resistor spring could be seen and very close to the body of the car. They often broke and shorted the coil frying it. The resistor on the pic is the one you would require. I had a 280CE with similar problems.


    [​IMG]
     
    Last edited: Oct 26, 2008
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