R129 1991 500SL Turns Over But Will not Fire

Discussion in 'Electronics' started by GregE240, Aug 31, 2016.

  1. GregE240

    GregE240 Active Member

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    Hi there

    Been a while! I hope everyone is well?

    I've got a problem with my SL - I suspect it is immobiliser related but hope someone can offer me some advice. I went to start my car earlier and as it has been a while, I let the immobiliser kick in so the engine would turn and not fire. I then usually lock and unlock the door by sticking a key out the window, but this time - nothing.

    I have bought new batteries for the key - its not that. I've disconnected and reconnected the battery - same (battery / car has been on CTEK conditioner and turns over engine easily). I've checked the OVR fuses - look fine.

    I'm at a loss - any assistance appreciated. I'd call the AA as I'm a member but I suspect they won't have a clue, hence asking for advice!

    Many thanks
    Greg
     
  2. RichardF

    RichardF Active Member

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    Is it an aftermarket immobiliser? They usually isolate the fuel pump.

    You might be surprised @ the AA, many of the guys are "time served" and used to dealing with stuff like this. A while ago I worked for a main dealer, they liked recruiting roadside assistant guys into the workshop, more experienced @ problem solving.
     
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    GregE240

    GregE240 Active Member

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    Hi Richard - no, its OEM with the green and red lights in the doors and bootlid button.

    What is does do is kill the fuel pumps, as I don't hear them pressurizing when I turn the key, nothing.
     
  4. d w124

    d w124 Hardcore MB Enthusiast

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    Do these have have ovp relay
     
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    GregE240

    GregE240 Active Member

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    Hi - yes, checked both fuses, both fine
     
  6. d w124

    d w124 Hardcore MB Enthusiast

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    It might be the relay itself.Fuses on these hardly ever go
     
  7. Dec

    Dec MB Enthusiast

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    Try, a few times, to synchronising the remote key fob.

    Can you see a Blue/White light through a digital camera when button is pressed?

    Dec

    [​IMG]

    [​IMG]
     
    1 person likes this.
  8. RichardF

    RichardF Active Member

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    Try reseating the connectors for the locking system and alarm with some contact cleaner.
     
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    GregE240

    GregE240 Active Member

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    Where is all of that, Richard?
     
  10. RichardF

    RichardF Active Member

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    It's the units in the boot on the drivers side above the battery, doing this rejuvenated my alarm/immobiliser.
     
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    GregE240

    GregE240 Active Member

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    I'll give that a go. Many thanks!
     
  12. rorf

    rorf Active Member

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    GregE240

    GregE240 Active Member

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    You're a star sir! I shall investigate!

    Many thanks!
     
  14. IBN

    IBN Active Member

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    Hi I had a similar problem with my 300SL last year and it turned out to be a faulty MAS Unit.... dealer wanted €800 for a new one, bought a second-hand one off someone on this site and it fixed the problem.
     
  15. RichardF

    RichardF Active Member

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    A good point, have you tried reading the codes?
     
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    GregE240

    GregE240 Active Member

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    Haven't got anything to read them with.

    OK, so tonight, I have:

    - bought contact cleaner;
    - removed and cleaned the connectors off both the black and white boxes adjacent to the vacuum pump in the boot.

    Sadly, no good. Richard also mentioned in another thread pulling fuse 5 and trying to start the car. Sadly, no good either.

    Symptoms remain:

    - at ignition position 2, the fuel pumps are not priming as they usually do;
    - both the remote keys have stopped working.

    Any other ideas? I am calling Green Flag tomorrow to get them to look at it, though I suspect a low-load to a specialist may be the order of the day....
     
  17. RichardF

    RichardF Active Member

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    Have you tried locking/unlocking manually?
    Worth googling code reader, it'll cost you pennies to build. And although the info is a bit limited it'll still prove invaluable in future trouble shooting.
     
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    GregE240

    GregE240 Active Member

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    Locking / unlocking manually works, but only the door the key is in. The vacuum system does not unlock everything / central locking.

    Is there a stick for this code reader? And where is the connector? Is it near the fuses or over near the ECUs?

    Thanks for your help with this Richard - much appreciated.
     
  19. alabbasi

    alabbasi MB Enthusiast

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    I'd start with the basics. Are you getting fuel to the engine? Is there a spark?
    Might be a good old fashioned non immobilizer problem.
     

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