.


... Deleted ...


.

 

thanks G G, we learn something every day.
I run 93 ,,99% of the time ,, some times i'll put in 103 ,, and yes the car runs a little better. the main thing to have is a AFR gauge.
it also takes the ecu a amount of time to adjust to the new octane, some times it may take 3 to 5 miles, any changes you make the ecu has to adjust, so yes running 89 oct. then switching to 91 or 93 the knock sensor would entice the ecu to change to make the engine run properly
Your engine in these cars will tell you everything if you just listen example: about 3 weeks ago i found a few drops of oil on my garage floor. went to find the leak, (found front seal leaking), took everything apart to replace the seal and find out why! replaced the seal and was going to reinstall the pulley when i felt a bump on the sealing area . after inspecting the pulley I found it cracked causing the oil leak and telling me something is wrong,,, the engine said, fix me before i explode the knock sensor did not pick up anything, but it was replaced just incase. jim

 

Bit of a PBI there " engines designed can adjust for all grades of gas, based on its sensors pioneered by the knock sensor". This is true only if the advance maps can accomodate the different fuel (higher octane needs more advance, lower octane less).

The problem is that as a lower octane needs more advance, if it goes into detonation, the knock sensor will pull back the timing when what you really need is a higher manifold vacuum (MAP).

This is where the flex fuel capability of my Jeep is nice because it can handle anything from 85 octane to 115. I doubt that my Crossie's maps are that extenive. The tuners should know.

Personally I usually alternate 89 and 93 filling at a 1/2 tank.

btw the secret to high compression and 87 PON is variable valve timing. This lets the engine avoid detonation by dialing back the maximum cyl pressure without affecting the timing. Engines designed in this century have it.

ps if you monitor the injector pulse width with an OBD scanner you can develop a feel for the AFR. A good scanner can interpolate IPW, MAP, TPS, and a load value to generate the AFR. Or can just look at the O2 transitions.

 

.


... Deleted ...


.