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W126 Woes

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by acme8850, Oct 28, 2012.

  1. acme8850

    acme8850 Active Member

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    Hi all,
    I have recently been experiencing problems with my W126, it is an 88 300SE. Auto
    starts and runs fine when cold, revs cleanly with no issues.
    However when warm it does not like to pull away. engine running fine, stopped at lights or junction, go to pull away engine splutters and misfires, then dies. Restarting is a challenge spinning over fine but not starting then finally catches, runs rough and misfires on startup, but once restarted and reved up it clears and runs fine again, drop it into drive to pull away and it bogs down and dies again. I have managed to overcome the bogging by holding revs high and dropping it into drive to get it home, it still splutters as it comes under load but it will pick up and run ok if the revs can be kept high enough. If revs are at tickover when drive is engaged then it just dies as throttle is applied.
    Any advice or assistance in diagnosing the fault is gratefully recieved.

    Thanks
     
  2. lwbnick

    lwbnick Senior Member

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    Location:
    wales
    Your Mercedes:
    expedition
    Check the dizzy cap, they crack and cause all sorts of hot running problems.
     
  3. television

    television Always remembered RIP

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    Location:
    Daventry
    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    As above, is the car ok once it is up to full temp after running a while
     
  4. maska

    maska Senior Member

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    Your Mercedes:
    E Class
    Had The same problem; Replaced CIS , [4pin] Type ,No more missing or stalling ! [touch wood] ,:D:D
     
    Last edited: Oct 28, 2012
  5. william28ho

    william28ho Active Member

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    change the OVP relay....
     
  6. OP
    acme8850

    acme8850 Active Member

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    Hi,
    Thanks for the replies, I have checked the distributor cap, it looks almost new and has no noticable faults or cracks.
    Where do I find the OVP Relay and what and where is the CIS?
    apologies for my lack of knowledge.

    Regards
     
  7. television

    television Always remembered RIP

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    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    The OVP relay cannot affect a cold start or running, if faulty the idle would be bad all the time, is the car OK when hot
     
  8. OP
    acme8850

    acme8850 Active Member

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    Hi,
    It seems to run OK when warm but when put under load the problem appears.
    If anything it runs and performs better when cold.
    Regards
     
  9. television

    television Always remembered RIP

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    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
  10. OP
    acme8850

    acme8850 Active Member

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    Is it located in the fusbox, under the bonnet by the bulkhead on the drivers side?
     
  11. television

    television Always remembered RIP

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    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    [​IMG]Its at the rear somewhere,,if not under a cover on the bulkhead, iy has a fuse on top of the relay item 152
     
  12. OP
    acme8850

    acme8850 Active Member

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    Thanks very much Malcolm I'll check it out in the morning.
    Regards
     
  13. Gary Hanson

    Gary Hanson Senior Member

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    Your Mercedes:
    A Jag. Jags are my favourite.
    I had a Rover many years ago which was alright when started, until it was driven down the road. Then it spluttered and eventually stalled. I tried all the usual things, plugs, leads, cap, rotor arm. It turned out to be rain water which had got into the petrol tank via the filler neck which was rusty.
     
  14. OP
    acme8850

    acme8850 Active Member

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    The plot thickens........
    Had the car running on the drive today. all ok when cold but as it gets to temperature it starts to run eratically, when reved it clears, but at tickover when warm it is running quite lumpy.
    Looked at the OVP Relay, it has 2 fuses on the top, when they are removed individually the tickover speed increases, replacing the fuse tickover drops back again, does this suggest the relay is working OK?
    A further fault developed today, I wonder if this may be the root cause.

    The alternator is not working, battery runs down till flat and engine stops.
    This was not the case when the fault originally occured, but now, No ignition light on dash, or oil light. When blue light wire from alternator is earthed, lights come back on. I guess this means dead alternator, is that correct?
    Strange that it occured today, coincidence? or could the faulty alternator be the cause of the poor running when hot?

    what say you guys?
     
  15. television

    television Always remembered RIP

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    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    The site I use for the diagrams is not working tonight,,I will come back to it
     
  16. maska

    maska Senior Member

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    Your Mercedes:
    E Class
    Hi ; The CIS is on top of the head R/H rear, It usually Has 4 pins; Basically all it is, a veriable resistor, Governed By the engine temp; That regulates fuel from start-up, to normal running. I hope this helps. :)
     
    Last edited: Oct 30, 2012
  17. maska

    maska Senior Member

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    Hi, Have you fixed the Problem Yet !:?
     
  18. Steve169

    Steve169 New Member

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    Your Mercedes:
    1988 W126 420SEL
    Had a problem with my 420SEL start up fine but when warm started to run rough
    cough a wheeze then it would with draw and have a big chuck out the exhaust, run fine for 5 min then have another
    coughing fit with a great loss of power flat to the floor board just creeping alone the hwy . at max RPM
    Went in and out of the MB workshop they couldn't find the problem :(
    MMM was just thinking, I had this problem with my old car when I was younger,
    now what did I do to fix the problem,... Then it hit me was the flipping exhaust system.Could be that I have the same problem?
    So I Climbed more like crawled under my MB ouch!! 2 massive cats, 2 resonators and 1 massive muffler
    MMM what I have I got to loose, I`ve tried everything else, so out came the pipe cutter removed the lot right up to the
    engine pipes. I was quoted $1500.00 to replace with new MB system, no flipping way, I then turned the twin system into a single 2.5 inch pipe with one straight through Cat, one sports muffler.. Cost $340.00 fitted. Started up, purred like a kitten, yippee prob fixed, has been running perfect for 2 years now, touch wood .. The old system was so choked with gunk the motor couldn't breath. was still the original system and vehicle had down over 300.000ks . Its just the simple things that could save time and money may not always be the motor at fault. ``Happy Driving :)
     

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