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Discussion Starter #1
Since the last time i filled up with higher octane fuel my lie-o-meter registered 28.6 mpg.
Thats with about 10% city, 30% hiway and 60% 45mph country road driving at around 150 miles since the fill up.
And coasting safely as long as and where ever possible before stops.

Before been using cheaper 87 octane gas and my avg. mpg/lie-o-meter was around 25mpg with the same driving habits.
But at that last fill up been experimenting with higher octane fuels.

Don't really know at this point whats going on but i need to do some manual mpg calculations to see whats really going on.
Stay tuned!
 

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Using better quality fuel and driving conservatively can work. It's not the octane that's helping you...it's the better quality and better additives compared to "cheap" fuel. You may get similar results with "top tier regular" fuel. SUmmer temps and summer fuel also help .I only ever used 87 octane fuel (mostly Costco) with my JGC and mine was a V8. I generally got good fuel economy with it.
 
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Seasonal winter and summer additives can slightly affect results as well. Using ethanol free gas will definitely show an improvement, but at least around here the 89 octane ethanol free is the same price as premium so there aren’t many cost benefits with it.

Good old fashioned manual hand calculations are definitely better than the old “lie-o-meter!” In the EVIC! :)
 

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Using better quality fuel and driving conservatively can work. It's not the octane that's helping you...it's the better quality and better additives compared to "cheap" fuel. You may get similar results with "top tier regular" fuel. SUmmer temps and summer fuel also help .I only ever used 87 octane fuel (mostly Costco) with my JGC and mine was a V8. I generally got good fuel economy with it.
Thanks Jim, I also use most 87 from Costco with my Hemi and driveability and mileage are very good. When the difference between regular and premium was 10 cents per gallon it was an easy choice. With it now hovering around 40 cents in Florida not so much.
 

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Discussion Starter #5 (Edited)
Filled up today with a half empty tank with 89 octane gas then reset my lie-o-meter before leaving the gas station.
Documented the mileage and amount of fuel to fill up.
The next fill up will tell the truth one way or another.

After that fill up and around 80 some miles of driving my lie-o-meter read 28.7 mpg before parking for the day.
I only fill up at no-name non top tier gas at a couple stations around here.
I don't know but this seems too good to be true, the manual calc will tell the truth.

In hot weather with a hot engine and the accompanying hot air intake, some engines especially under load will have a tendency to ping maybe unperceivable to the ear.

So now the $64 question?
Do these modern computerized controlled engines monitor the knock or other sensors and adjust the ignition timing accordingly?
With higher octane fuel in hot weather conditions it sure seems my engine has more pep though i'll admit without a dyno workup it could be a placebo effect.

I do know for a fact though that in hot weather my F150's coyote V8 engine does have noticeable improved performance with 93 octane fuel. This is also verified too by others on F150 forums.
And like my GC's owner's manual my F150's manual also suggests using 87 octane?

Been doing a search on if or how the Pentastar engine can/does adjusts ignition timing on the fly dependent on fuel octane.
Nothing so far although have found that others say that some engines do adjust ignition timing on the fly depending on the octane of fuel used.
Without a FCA engineer chiming in, this will be an endless mystery.
 

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89.7 mpg is phenomenal, I'd hang on to that Jeep! 🤣
 
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Discussion Starter #7
89.7 mpg is phenomenal, I'd hang on to that Jeep! 🤣
Haha you caught a typo in my previous post. Thanks for that!
My bad, should be 28.7 mpg instead. Maybe that was subliminal wishful thinking!:)

Still i'm looking forward for the next fillup.
Can't wait til i determine the accuracy of the lie-o-meter.
 

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So now the $64 question?
Do these modern computerized controlled engines monitor the knock or other sensors and adjust the ignition timing accordingly?
With higher octane fuel in hot weather conditions it sure seems my engine has more pep though i'll admit without a dyno workup it could be a placebo effect.

I do know for a fact though that in hot weather my F150's coyote V8 engine does have noticeable improved performance with 93 octane fuel. This is also verified too by others on F150 forums.
And like my GC's owner's manual my F150's manual also suggests using 87 octane?

Been doing a search on if or how the Pentastar engine can/does adjusts ignition timing on the fly dependent on fuel octane.
Nothing so far although have found that others say that some engines do adjust ignition timing on the fly depending on the octane of fuel used.
Without a FCA engineer chiming in, this will be an endless mystery.
These FCA engines can definitely detect knock and retard timing accordingly. The reason the owner’s manual says premium is not needed and not recommended is that the engine is programmed for 87 octane (V6) or 89 octane (V8) and can’t take advantage of the higher octane unless modified by a tuner. The knock sensors are there to guard against detonation, not take advantage of higher than recommended octane.
 

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Discussion Starter #9
These FCA engines can definitely detect knock and retard timing accordingly. The reason the owner’s manual says premium is not needed and not recommended is that the engine is programmed for 87 octane (V6) or 89 octane (V8) and can’t take advantage of the higher octane unless modified by a tuner. The knock sensors are there to guard against detonation, not take advantage of higher than recommended octane.
Do you have a link for these Pentastar engines retarding ignition timing via knock sensor data?

Thats what i'm thinking that the PCM can retard ignition and maybe even vary valve timing dependent on knock senor data.

But here's the thing as i mentioned earlier.
These latest Pentastars have a 11.3 compression ratio.
Couple that with hot weather, hot air intake and under heavy loads where even a slight ping is detected by the PCM.
The PCM then could very well retard ignition and maybe even valve timing sacrificing performance and accompanying gas mileage.

I do know that my F150's V8 engine performs better in hot weather when using 93 octane gas.
 

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he reason the owner’s manual says premium is not needed and not recommended is that the engine is programmed for 87 octane (V6) or 89 octane (V8) and can’t take advantage of the higher octane unless modified by a tuner.
The Hemi V8 is programmed to run very well on 87 and run optimally on 89. I never put a tank of anything other than 87 in mine. Neither engine will benefit from higher octane than that other than perhaps the increased additives in some "premium" fuels.
 
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Discussion Starter #11
The Hemi V8 is programmed to run very well on 87 and run optimally on 89. I never put a tank of anything other than 87 in mine. Neither engine will benefit from higher octane than that other than perhaps the increased additives in some "premium" fuels.
Jim, I would tend to agree with that in cool to cold weather.

Its on those extremely hot days where engines have a slight noticeable reduction in power especially under load such as driving up a hill or pulling away from a stop where pinging could happen.
Keeping in mind that less denser hot air intake does have a major impact on engine performance in hot weather but If there's going to be any pinging going on thats when it would happen.

Yeah in those cases, the transmission would kick down a gear (if not in 1st gear) but it could be a race between any PCM pinging detection and the downshift.

11.3 compression ratio + extremely hot weather + modern lean fuel/air ratios + heavy load = pre-ignition.

If the PCM can and does decide to retard the ignition timing due to pinging detection, how long would that be?
Temporary fixed time? Until no pinging is detected? Until the next engine start cycle?

Back in the olden days before PCM ignition control and unleaded gas, engine pinging was a relatively common occurrence.
The easiest solution was to either down shift, switch to a higher octane gas and if that didn't work time to check the ignition timing.
Maybe i've been lucky but I have never experienced pinging in any modern PCM controlled vehicles and i've owned a lot of them and old school non-PCM vehicles both past and present.
 

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In the seven + years I drove my MY12 with the Hemi, never once did I experience pinging on 87 octane fuel, including when visiting the 'rents in Florida. Same when towing north of 5500 lbs with a live load. (horses)
 

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The Hemi V8 is programmed to run very well on 87 and run optimally on 89. I never put a tank of anything other than 87 in mine. Neither engine will benefit from higher octane than that other than perhaps the increased additives in some "premium" fuels.
Yes, not long after purchasing mine, just for fun I tried a few tanks of premium and could not tell any difference in performance or gas mileage which convinced me that FCA (and you) are correct. I then switched to 87 using “Top Tier” approved brands for detergent additives and have been fine since.
 
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Since the last time i filled up with higher octane fuel my lie-o-meter registered 28.6 mpg.
Thats with about 10% city, 30% hiway and 60% 45mph country road driving at around 150 miles since the fill up.
And coasting safely as long as and where ever possible before stops.

Before been using cheaper 87 octane gas and my avg. mpg/lie-o-meter was around 25mpg with the same driving habits.
But at that last fill up been experimenting with higher octane fuels.

Don't really know at this point whats going on but i need to do some manual mpg calculations to see whats really going on.
Stay tuned!
I had a 2015 JGC Laredo w/3.6 engine and never used anything other than non-ethanol gas, which gave 25 mpg in city driving. I’m now in a 2020 JGC with same engine (-350 miles) and as soon as I get near empty I’ll only be using non-ethanol gas, which is readily available in North Alabama. It’s 0.60/gallon more expensive but well worth the difference in terms of mpg and smooth operation. This ethanol mandate is purely a political sop to the corn belt.
 

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Discussion Starter #15
In the seven + years I drove my MY12 with the Hemi, never once did I experience pinging on 87 octane fuel, including when visiting the 'rents in Florida. Same when towing north of 5500 lbs with a live load. (horses)
Jim, thats because the PCM could be retarding ignition timing on the fly when it detects a pinging event.
As i've said earlier, i also have never experienced pinging with modern PCM controlled vehicles in hot or any other kind of weather.
Thats basically my point.
 

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Discussion Starter #16
I had a 2015 JGC Laredo w/3.6 engine and never used anything other than non-ethanol gas, which gave 25 mpg in city driving. I’m now in a 2020 JGC with same engine (-350 miles) and as soon as I get near empty I’ll only be using non-ethanol gas, which is readily available in North Alabama. It’s 0.60/gallon more expensive but well worth the difference in terms of mpg and smooth operation. This ethanol mandate is purely a political sop to the corn belt.
I think i agree with that idlewind.
E85 in my flex fuel F150 when i tried it once gave noticeably better performance but lousy gas mileage.
It all boils down to one's priorities, money saved or personal lead footing driving habits where money is not an object.

My interest in all this is just basic curiosity on what the PCM can do when it detects a pinging situation.
 

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I’ll only be using non-ethanol gas, which is readily available in North Alabama
Unfortunately, Ethanol free gasoline is pretty much not readily available to many of us, so "top tier" is about the best we can do.
 

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Gas mileage goes up with higher octane fuel if the engine is built to take advantage of it. Higher octane = more power in the engines designed to use it. More power = more efficient use of the gas.

Investing a lot of mental sweat on calculating details of gas mileage is, IMO, a waste of time in a mid-size SUV.

It's a Jeep and I didn't buy it for gas mileage. I'll be happy with reasonably consistent mileage performance based on the current weather and traffic conditions.You can change the mileage on any tank with minor variations in driving, so worrying about tenths of an MPG is primarily an intellectual but impractical exercise.
 

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I've experimented with several tanks of gas alternating 87 and 91 in my 5.7. It runs ok on 87 but better on 91. On 87 you can feel it flat spot when the computer kicks the "timing" back a notch on incipient ping or whatever it is it's sensing and adjusting. If there's a mpg difference I haven't noticed it.
 

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Discussion Starter #20
I've experimented with several tanks of gas alternating 87 and 91 in my 5.7. It runs ok on 87 but better on 91. On 87 you can feel it flat spot when the computer kicks the "timing" back a notch on incipient ping or whatever it is it's sensing and adjusting. If there's a mpg difference I haven't noticed it.
Wish we had 91 octane available at the gas stations around here.
Its only 87, 89 and then jumps way up to 93 octane.
There is a considerable price/gallon differential between 87 and 93 octane.
91 octane could be a good compromise money wise especially for Summer driving.

My next experiment might be to see if there's any kind of a difference between 89 and 93 octane.
I did fill up with 93 octane once way back when when i did the 0 to 60 time test.
Still working on my current lie-o-meter accuracy test.
Since that last fill up a few days ago and some 150 miles later its reading 28.6 avg. mpg again.
 
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