Ok... I have generally been running regular 87 octane gasoline with no adverse effect. Then I recently changed the plugs to the NGK Iridiums and I have now experienced excessive pinging under WOT. I have put a fresh tank of Premium in to test and that has solved the problem.

Now... why did the new spark plugs change the tolerance to 87 octane? They were factory gapped to 0.052" which is what my research had said they were supposed to be set at. Why isn't the knock sensor doing it's job?

Anyone have any ideas?

 

Just a guess - the irridium plugs have tiny electrodes which may get hotter and retain a higher temperature - causing themal pre-ignition in the 87 octane fuel, which the knock sensors can't control by retarding spark, but higher octane fuel can... again, just educated supposition.

 

That's what would worry me. There should have been a noticeable performance penalty when using 87 octane and none when switching to high octane. Was this present?

 

Could it be that you got a bad batch of fuel and the plugs are OK?

 

fuel trims affected by such a 'drastic' change with the new plugs? (not speculating exactly how). Just stick with premium or go back to 87 and do a hard reset. You'll start from scratch on the trims and perhaps avoid the knocking.

 

If the low octane fuel is occasionally igniting, under compressive load, due to the overheated, fine wire, irridium electrodes (and not from the spark), retarding timing from knock sensor information won't help... ergo my supposition in post #2.

But yes, one would expect to see a performance improvement when the knocking/pinging stops, as the timing, no longer being retarded by the sensed knocks, should advance back to normal.

 

Concise Quad!

 

Great replies and all have been considered except the nicely detailed description from Quad!

I have ruled out fuel quality, as I shrugged it off the first time it happened, about 4 weeks ago. I fuel up approximately every four days with anywhere from 15 to 18 gallons each time. That means roughly 5 tanks of fuel including the premium that is in it now!

As to the performance of the previously with 87 octane, I had noticed very little performance degradation for casual driving with the occasional WOT run. If I were to take it to a track I would probably see the real effects.

One supposition that I have is that the fuel has been reformulated for winter? I know in the days of MTBE, there were winter formulations and subsequent spring /summer formulations. I'm not sure if that is the case now that all we get is the crappy ethanol mix. Does anyone know if that is the case? I may have just done my plug switch at roughly the same time and am now battling a different externally induced issue.

I will do another WOT test this evening to just be sure that the 92 octane has truly solved the issue. I'm not sure I care if I continue to run premium, but it is a bit annoying that I cannot run 87 any longer. I may try H20boys idea of the hard reset just to see what happens. If I remember correctly, that is initiated by removing the negative lead and shorting it to the positive battery terminal?

 

First you should never ever run an r supercharged anything on 87. Only premium grade. Unless you never go into boost, and since you said wot youre there. And if you can hear it youre hammering the bearings and pistons. While ive long said for normally aspirated its ok to not run premium as long as
1) youre not towing or have 5 big people in the car
2) you dont live in a hilly area that loads the engine more.
3)YOU DON'T HAVE AN R!!!!
Then again there are those that feel only the BEST should go in their Jaguaaaaar, gas, oil, distilled or Avion water. etc....

 

Brutal... now, tell us what you really think! :-)

 

Oh.. i didn't even notice that you have an R... This just makes my scenario that much more likely - low octane while adding boost along with hot electrodes is just asking for pre-ignition - along with the concomitant damage it can generate. I'd really bite the bullet and spend the extra two bucks a tank - compare that to the cost of new pistons or bearings... it's extremely CHEAP! Knock sensors can't control pre-ignition.