500SL R129 - Still Immobilised...

Discussion in 'Electronics' started by GregE240, Apr 17, 2017.

  1. GregE240

    GregE240 Active Member

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    Location:
    Northamptonshire, UK
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    1990 500SL
    Hi there,

    I posted last year about my poorly SL - it's a 1990 with the MBSS and UK immobiliser. I've still got the non-starting issue with it. About time I got it sorted for summer!

    Basically- I think the immobiliser has its knickers in a twist as the engine will turn over but won't start. The reason I think it's immobiliser related is because at position 2 you don't hear the fuel pumps priming. In addition, the central locking has stopped working, and each door and the boot will only unlock with the key.

    The battery is less than a year old and is trickle charged. I've disconnected it for 3 weeks and reconnected it, still the same.

    Ive heard about K38 relays but I think my car may be too early for one of those?

    Any advice appreciated!
     
  2. Dec

    Dec MB Enthusiast

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  3. Sp!ke

    Sp!ke Administrator

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    start on the simple things.

    Are you getting a spark?
    Check your fuses very carefully.
    If you bridge the fuel pump relay does the pump prime?
    Have you checked/cleaned your distributor caps?
    Have you done the ovp relay test?
     
    Last edited: Apr 17, 2017
  4. OP
    OP
    GregE240

    GregE240 Active Member

    Messages:
    952
    Joined:
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    Location:
    Northamptonshire, UK
    Car:
    1990 500SL
    Hi Spike good to hear from you.

    To answer your questions:
    Spark - yes
    Fuses are all fine
    Where is the fuel pump relay? What do I need to bridge?
    Caps & rotors fine
    Got a link to the Ovp Test?

    I had Green Flag here a while back. They checked the basics, and if you squirt fuel into the inlet, the engine runs, but dies when that fuel supply is stopped.

    I'm sure the immobiliser has kicked in and needs some sort of reset as the doors won't lock or unlock via the single button on the key?

    In normal circumstances from unlock you have about one minute to start the engine, otherwise the immobiliser kicks in and gives you the symptoms in that the engine turns but doesn't fire as it kills the fuel pumps. A lock and unlock of the car via the key button usually sorts this, or has until now?
     
  5. OP
    OP
    GregE240

    GregE240 Active Member

    Messages:
    952
    Joined:
    Dec 30, 2002
    Location:
    Northamptonshire, UK
    Car:
    1990 500SL
  6. Dec

    Dec MB Enthusiast

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    Take pictures when you are in there.

    Dec
     
  7. brucemillar

    brucemillar MB Enthusiast

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    C55 AMG Wagon - W124 300te 4matic Wagon - BMW 4.8is X5 E53 - SWB Pajero 3.5 V6 24v
    Apologies if I state the obvious.

    If it runs when you squirt fuel in by hand? That says, everything is working on the spark and timing side and suggests that the pump(s) are not running. Can you hear the pump prime and running? WARNING: Some alarms allow the pump to prime, then cut off after a few seconds. To test this? Crack a fuel line at the engine and crank the engine. You should get a constant flow of fuel while cranking.

    If it helps (probably not) on my 124: I gave up and we ripped out the alarm/immobiliser. We just could not figure out what it was doing and when (it was not allowing the engine to fire) I have not had a problem since!!
     

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