Second Spark Plug change at 85123 miles

Its all good.

 

No worries

 

Wait... What? You do know that going up an octane doesn't do anything unless you tune your ecu/engine for it right? If you are using shell (which I do as well), all their octanes have basically the same detergent for keeping the deposits in check. It'll be cheaper and better to just use a fuel system cleaner once in a while than keep buying premium gas.

As for the oil, I guess you can do that. Or you can push it to 10k and buy test kits instead. You send a sample of your old oil out to check for contaminants and metal if you are paranoid.

 

Top tier fuels are good but you don’t need 93. I run Exxon 87 and use Amsoil PI every 5K. My 4.0L sees no difference with higher octane.

 

Is there ECU ignition multiplier data to support that higher than 87 octane does nothing in these engines? Many fuel injection systems that I have seen ECU info about constantly try to advance ignition timing, especially in low load closed loop conditions, to extract maximum efficiency and MPG. To do this, they advance timing until either the ignition multiplier is maxed out or there is fine knock detected and then it backs off slightly with timing to alleviate the knock and this repeats endlessly. Checking the ignition advance multiplier (as Denso calls it in my experience) or the rough and fine learning knock correction tables will indicate if a higher octane fuel could be of use for more efficiency/tq (or it could indicate other issues).

 

I knew I was going to get feed back on this topic of 93 octane, I get better mileage and no valve noise when I have the air condition on at take off and the owners manual says 87 and up octane how can it hurt to have a better burning fuel.

 

Higher octane fuel burns slower & is harder to ignite than lower octane fuel. Seems odd that faster burning & easier to ignite is worse than harder to ignite & slower burning.

 

it resists ignition more but I have never heard that it is "slower burning". What does that mean? the flame front propagates slower? Sounds like some BS someone interpreted.

more resistance to ignition is not a bad thing at all, within reason. A fuel that ignites too easily may ignite before the spark plug fires if there are high cylinder temps and pressures. That is why higher octane rating fuel is necessary for boosted and high compression engine. If the overall cylinder delta pressure is such that the air/fuel mixture can ignite from the compression caused temperature increase, pre-ignition and knock can/will result.