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  1. #1
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    Default Missing spark

    Hey all,
    Running into an intermittent problem with the R12. Cold starts take a long, long time but hot restarts are proving tricky. Starter motor cranks fine, but it's as though there's no spark at the plug. Would it be the leads/plugs? Thought it was symptomatic of a failing battery, but replacing it doesn't seem to have solved anything.
    Any clues?
    Cheers, Barry

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  2. #2
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    Hi One.four
    Quite possible the plug leads. They die with time and heat. My suggestion is to start the car, if possible , in the dark or a dark place, and look at the leads while you give the motor bursts at full throttle. You will see the spark flashing probably, in many places as it leaks away. The method is to load the motor as much as possible to full compression not to rev it high.

    So look at the leads, plug caps, the dissy cap, the coil top etc. Might be a surprise to you. Of course a good clean of all the above might help for a start as well as plugs and points for a standard tune-up, of course.

    Re reading your post I think that I assumed you had given it a tune-up. A standard ignition tune-up check would be the first step really when there is hard starting. Check and adjust or replace the points/capacitor, set timing, check and gap or replace plugs, Clean plug leads, dissy cap, check cap terminals, rotor button etc.
    Good luck Jaahn
    Last edited by jaahn; 16th July 2017 at 10:57 AM.

  3. #3
    COL
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    Apart from what Jaahn has said, from experience the rubbing block on the points wear down closing up the points, changing the dwell and also the timing.

    I would first check the points to make sure that they are clean with no pits or lumps on them, then check to make sure the gap is correct.
    Regards Col

    1973 Renault R12 Station Wagon
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  4. #4
    1000+ Posts REN TIN TIN's Avatar
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    Ditto all the above and especially the points.
    Apart from the rubbing block wearing, it's not unknown for the screw holding the points to come loose and close up the gap.

    Also, check for an air leaks, mainly perished hoses or leaking manifold gasket. Even the carby base and spindle and if you have a TS, check the brake booster for leaks.



    Cheers
    Ren
    "I cannot help but notice that there is no problem between us that cannot be solved by your departure. Mark Twain"

  5. #5
    1000+ Posts alan moore's Avatar
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    First check you actually have no spark when it is hot. It can be that the fine wire inside the coil opens when it gets hot, to then touch back together when the coil cools.

  6. #6
    Too many posts! JohnW's Avatar
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    And??

    Any joy?

    Cheers
    JohnW

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    I'd also check the carbon rod inside the distributor, if the dizzy gets worn, the distributor rotor tracks off centre and the carbon rod will break off or wear down till all that is there, is the little spring flopping about that helps compensate for wear. Had that several times in the Fuego and a new cap or replacement of the carbon rod makes a world of difference. Some distributor caps can crack or surface track and the carbon dust lodges in the crack and a bit of moisture sends the spark to ground at the base of the cap.

    Hope that helps.

  8. #8
    1000+ Posts renault8&10's Avatar
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    And if all that fails either replace the rotor button or gently sandpaper the contact edge. I've had an R12 engined car that failed to start. The solution at hand was to take the rotor button out and drag the edge along the footpath to clean the surface up.
    KB


  9. #9
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    Also check distributor bushes.
    If they are worn, the shaft will run eccentrically causing all kinds of ignition mis-timing

  10. #10
    bob
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    Default Froggy dizzys

    G'day,

    Quote Originally Posted by driven View Post
    Also check distributor bushes.
    If they are worn, the shaft will run eccentrically causing all kinds of ignition mis-timing
    This was a problem in a 12 that I had years ago, as I recall, it wasn't particularly old at the time either !! New bushes made a BIG difference to how it ran.

    The elusive dizzy problem I've found in r20, 504, 404 is earthing. Some clever fella in the design department decided that they could save heaps by removing the tiny bit of braided cable between the dizzy body and the action plate and rely on all the grotty bits sliding around to provide a decent electrical connection.

    Makes for real head-scratcher until you realise the problem. Usual symptom for mine was it would run fine from cold until the thermostat opened, this allowed the vacuum to reach the dizzy, moving the action plate a little and buggering the connection - but only if the sequence of events called for moving away from stationary, the buggers would stutter or stall. Warm up whilst moving was OK, like I said, bloody head-scratcher.

    Best way to avoid a lot of these problems is probably to fit electronic switching.

    cheers,
    Bob

  11. #11
    Too many posts! JohnW's Avatar
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    Yes, Hot Spark kits are great, as I say whenever I'm given the slightest opportunity. That's the cheapest "in" but does need the distributor to be in OK condition regarding advance-retard systems.
    JohnW

    Renault 4CV 1950 (R1062)
    Renault R8 1965 (R1130)
    Renault Scenic Series II 2005 (wife's)
    Renault Scenic Series II 2006 (daughter's)
    Renault Scenic Series II 2007 (mine)

    CitroŽn CX Pallas 1980 (moved on to new custodian)

    National Co-ordinator, Renault 4CV Register of Australia

  12. #12
    1000+ Posts Wildebeest's Avatar
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    Onefour,
    Does your ignition system have a ballast [Blast!] resistor attached to the coil ? By pass this or change the system, replace coil with 12 volt/no resistor.
    I'm with JW here with the Hot Spark system.

    Valiants had resistors, to get them going we would just by-pass them until warmed up.

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