31447fa0   
   On Thu, 24 Sep 2009 19:53:31 -0700 (PDT), studio    
   wrote:   
      
   >On Sep 23, 8:02 pm, cl...@snyder.on.ca wrote:   
   >> I put Iridiums in my Chrysler PT Cruiser - and a couple months later I   
   >> developed a #1 misfire at idle.. I ruled out plug wires and coils by   
   >> switching them, and figured I'd switch plugs between #1 and #4 to see   
   >> if the misfire followed the plug.   
   >>   
   >> Misfire went away.   
   >>   
   >> It appears ONE of the plugs wasn't happy firing "backwards".   
   >   
   >Strange that it would develop an unhappiness months later. Or that one   
   >plug would be unhappy and the other not.   
   >Sounds more like a faulty wire connection problem to me.   
   >   
   >> That's the only experience I've had with Iridium or "fine wire" plugs   
   >> in the last 20 odd years.   
   >   
   >Did you check your gas mileage at all, or notice any other   
   >improvements?   
   Definitely not a wire or connection problem - and I've been a licenced   
   mechanic since 1971 - wrenching since I was 15 in 1968.   
   The misfire was getting progressively worse. When I first noticed it,   
   there were not even any "incipient" codes registered on the ECU.   
   When I decided to really dig into it was after it misfired regularly   
   enough to actually set the code and turn on the CEL.   
   The misfire only occured under 1500 RMP and basically under 1200 - at   
   or just off idle in gear only. If I reset the ECU and drove down the   
   highway there was no misfire detected - so I doubt there was MUCH   
   effect on mileage.   
   Spark plugs can be strange - years ago in the days of leaded high   
   sulphur fuel we had lots of trouble with plugs "glazing" - a light   
   yellow-green glaze would build up oin the insulator cone that was a   
   semi-conductor and under certain conditions would short out.   
   The coating was Lead Sulphide - otherwise known as Galena   
      
   I suspect there was something similar going on with these plugs,   
   although there is no lead in Canadian motor fuel any more. Sulphur   
   levels are getting much lower now too - but PERHAPS I may have put   
   some aged 2 stroke fuel  into the tank in low quantities that was   
   mixed from 100LL AvGAs.  It would have only been a couple of liters at   
   most of 50:1 in 50 liters of unleaded regular so I doubt that was the   
   mechanism involved - and the insulators looked PERFECTLY clean.   
      
   At any rate, one plug either shorted or would not fire when reverse   
   polarized.   
      
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    * Origin: you cannot sedate... all the things you hate (1:229/2)