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Thread: Knock Retard

  1. Default

    Hope you get the issue sorted soon Jmac.

    On a side note I replaced the OEM plugs with one step colder and I haven't had any KR issues with the car since.

  2. #22

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    Give it time

  3. #23

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    sorry to go abit off topic but what is the difference in going 1 step colder or 2 steps colder?

  4. #24

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    You essentially need to match the temperature rating of the plugs to the operating characteristics of the engine. If the plugs run too cold they will foul and accumulate deposits that may cause pre-ignition. If they run too hot they will be physically damaged, wear out quickly and have hot spots that may cause pre-ignition. You get the idea.

    High performance engines run higher cylinder pressures and higher temperatures. So they need colder plugs than a stock engine.

    Hot plugs are called hot because they stay at a higher temperature, because they have less of a heat dissipation pathway to conduct heat away into the cylinder head. In some cases they also poke further into the combustion chamber. Cold plugs are of course the opposite.

    At this point it gets complicated because by now you've probably gathered that a cold plug because of its shape may have less reach and is less exposed to the air/fuel mixture in the combustion chamber. Which can adversely affect combustion, so colder plugs aren't automatically better.

    However, if you're still with me at this point, and this is just a wacky theory, I suspect that the direct injection environment inside the combustion chamber of the turbo Mazda engine is too wet and too dense for the stock plug and is causing some spark blow-out. So the colder plugs, being less exposed, are less likely to have their spark blown out. Which is why our engines seem to run better with them, particularly under high load when lots of air and fuel is going into the cylinder.

    For the same reason, our engines tend to respond better to smaller plug gaps, but don't don't go too small or the engine wont run well at high rpm. I did an experiment where I gapped a spare set of plugs from 1.2mm down to 0.6mm and the engine ran beautifully smooth, better than it had ever run, just not at high rpm. I took that result as tending to confirm my theory.

    To finally answer your question; 1 step colder plugs tend to work well on a stock DISI engine, but 2 steps colder would probably result in plug fouling unless the engine was highly modified.
    Last edited by kmh001; 21-08-2009 at 09:30 PM.

    Gone to Volvo


  5. #25

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    stupid question atm.. but under which category and sub category is knock retard for our vehicles on the dashhawk??

  6. #26

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    I have also experienced knock retard values greater than 2 degrees.

    What I have found is:
    After maintaining a constant speed for a time (ie. 1 minute) at about 1900 rpm, apply a tiny bit more accelerator and watch the knock retard. Mine regularly jumps for about 5 seconds to 2 - 4 or so degrees.

    My car did it today after travelling through a school 40km/h zone in 4th, when I gently accelerated back up to 60.
    In this instance I don't believe it is real knock but the ECU retarding timing, but it is output as knock retard on the ODB2 port. I also hope to hook up an oscilliscope to the actual knock sensor to determine this some day soon.

    What is a worry is when you see knock under high load on WOT at higher revs - which happily I don't.

    Regards, Syd.

  7. #27
    Join Date
    Jan 2009
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    Default

    I have noticed my IGN value going into negatives with my Scangauge and have only noticed only when I back off the throttle after acceleration.

    Have only noticed it like -1 or -2 though, nothing out of control.

    I have noticed it not as much since I have gone to BP Ultimate as well.

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