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Unread 05-07-2013, 08:35 PM   #1
4x4andmetal
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Octane Rating

This sounds kind of stupid to me, but I thought I would fond out for sure. Will running higher octane fuel provide more power/mileage? A friend told me it did in his Toyota Tundra, but that's not a Jeep.

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Unread 05-07-2013, 08:41 PM   #2
jt_armstrong
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To the best of my understanding the octane level has to do with how much you can compress the fuel/ air mixture before it self detonates (pre-ignition). I don't think it provides any more power in its own right but it may allow the engine to alter its power curve to better release some more power.
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Unread 05-07-2013, 08:59 PM   #3
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My grandfather has a 2013 Kia optima and he said he filled it once with regular and another time with premium and he said he got better mpg with the premium. Not a jeep though
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Unread 05-07-2013, 09:04 PM   #4
KyleSekora
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Originally Posted by jt_armstrong View Post
To the best of my understanding the octane level has to do with how much you can compress the fuel/ air mixture before it self detonates (pre-ignition). I don't think it provides any more power in its own right but it may allow the engine to alter its power curve to better release some more power.
This is right. The higher the octane rating the more it compresses before it self detonates. Run the octane that the manual says to (which is just regular cheap-o gas, with no ethanol if you.can find it), because IIRC running an octane rating that is to high can cause engine knock.
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Unread 05-07-2013, 09:13 PM   #5
ratmonkey
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these vehicles can't self optimize for the extra timing running higher octane allows. there are no knock sensors.
if your jeep does get better mileage from high octane gas that means you have a problem with your motor. usually indicates heavy carbon build up in the combustion chamber.
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Unread 05-07-2013, 09:38 PM   #6
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these vehicles can't self optimize for the extra timing running higher octane allows. there are no knock sensors.
if your jeep does get better mileage from high octane gas that means you have a problem with your motor. usually indicates heavy carbon build up in the combustion chamber.
Will advancing the distributor a few degrees and running a higher octane do anything? Or am I thinking too old school here and the computer will retard it anyways? Did not know these Jeeps didn't have knock sensors. How's the timing controlled?
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Unread 05-07-2013, 10:06 PM   #7
dnuccio
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timings controlled by the pcm. turning the distributer wont do anything. at least thats what ive read on here
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Unread 05-08-2013, 04:54 AM   #8
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Originally Posted by wsigo View Post
Will advancing the distributor a few degrees and running a higher octane do anything? Or am I thinking too old school here and the computer will
retard it anyways? Did not know these Jeeps didn't have knock sensors. How's the timing controlled?
Turning the distributor takes the fuel injectors out of synch but doesn't alter timing. Spark events are triggered by grounding the coil secondary through the pcm.
Timing is set by a table based upon operating conditions including temperature, engine speed, load, and oxygen sensor data.
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Unread 05-08-2013, 06:10 AM   #9
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Using higher octane than factory recommended is just throwing money away. It does nothing but make your wallet lighter.

http://auto.howstuffworks.com/fuel-e...question90.htm
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Unread 05-08-2013, 06:13 AM   #10
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Thanks everyone. Guess I'll stick to 87.
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Unread 05-08-2013, 07:08 AM   #11
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Quote:
Originally Posted by ratmonkey View Post
Turning the distributor takes the fuel injectors out of synch but doesn't alter timing. Spark events are triggered by grounding the coil secondary through the pcm.
Timing is set by a table based upon operating conditions including temperature, engine speed, load, and oxygen sensor data.
Some real good info rat, thanks!

Curious if you can turn the distributor some on the V-8's but not the 4.0? When I installed a new distributor in my 96 4.0 there were 2 notches on the top of the distributor at the block the bracket fit into and there was no way to turn it even if you wanted too.

BTW, I ran plus grade 89 octane fuel in my ZJ for a while when gas was cheaper and saw no marked difference so went back to reg 87.
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Unread 05-08-2013, 08:42 AM   #12
ratmonkey
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V8 has notches too.
There's a very small window to allow for setting fuel injector synch. Which must be done with a dealer scan tool any time the distributor is removed.
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Unread 05-08-2013, 03:19 PM   #13
ZJMatt
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Originally Posted by KyleSekora View Post
This is right. The higher the octane rating the more it compresses before it self detonates. Run the octane that the manual says to (which is just regular cheap-o gas, with no ethanol if you.can find it), because IIRC running an octane rating that is to high can cause engine knock.
The first half of what you said is good, then you contradicted yourself. High octane fuel will REDUCE engine knock, also known as predetonation especially in high compression & forced induction engines. As you said it will reduce the likelihood of the fuel detonating before it's supposed to, which is the cause of "knock" or "ping."

I've owned two supercharged GTPs, one modded a little. And I had to run 93-octane from 7-11, ironically the cheapest place to get gas around. Saw lots of knock retard if I ran anything else.
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Unread 05-08-2013, 03:42 PM   #14
KyleSekora
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Originally Posted by ZJMatt View Post

The first half of what you said is good, then you contradicted yourself. High octane fuel will REDUCE engine knock, also known as predetonation especially in high compression & forced induction engines. As you said it will reduce the likelihood of the fuel detonating before it's supposed to, which is the cause of "knock" or "ping."

I've owned two supercharged GTPs, one modded a little. And I had to run 93-octane from 7-11, ironically the cheapest place to get gas around. Saw lots of knock retard if I ran anything else.
Ah. Thank you for correcting me.
I always have some to learn. I apologize for the confusion I may have caused.
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