Quote:
Originally Posted by dwarfnebula
The 4.0 Jeep 6 certainly can't take advantage of the ethanol because it has no knock sensor. Mine pings badly on the 85 octane they have around here, it needs mid grade. My Hyundai cares not, I've never heard it ping.
I remember hearing premium gas, even ethanol free, has fewer btus than low grade; can anyone corroborate this?
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I was hoping the lack of ethanol would help. Wasn't expecting a power / mileage increase from the higher octane. Wasn't expecting it to go down!
What year is your 4.0? Mine is a 2000 with coil on plug ignition and does have a knock sensor. I don't believe the older ones (or any 4.0 with distributor) has a knock sensor. I have been able to run non ethanol 85 (from a local indian reservation) in the summer and no knocking.
Higher octane gas has less energy and is slightly more resistant to igniting. Less energy means less heat expelled and less resistant to igniting means it won't light off based on heat in the cylinder like a lower grade gas would.
My focus *may* be able to see a slight improvement from higher grade gas. While it isn't higher compression, the ECU will try to advance the timing as far as possible until it knocks.
While I don't believe it can "sense" the octane of the gasoline, it is able to get an idea of the octane by how little/much it can advance/retard the timing.