po0dingles

So I had only assume it was regular, 87 octane but I was flipping through the manual and saw it stated something about 93 octane for my 5.2L. Now I'd assume the 5.9 would run premium but even mine?!

I've got a couple tanks of 87 through it and didn't notice anything wrong. Should I really be using 93???

Bustedback

87 is fine unless you hear pinging.

2WDUnderachiever

Knock sensor will probably keep there from being anything "wrong."

You aren't getting your full performance with 87, though... But the difference is marginal.

Run what you want.

dnuccio

my grandpa claims he gets 2-3 mpg better on premium. i just run 87 cuz its the cheapest lol

2WDUnderachiever

To add, I usually run 87 octane because I'm young and broke... But if my uncle's buying the gas, I put 91 octane in it, since that's what he puts in his Mustang.

I guess if someone whose wallet could take the beating was paying for my gas, I'd put 91 octane in it, but me...? Nahhh, 87.

jnicewan

Higher octane burns slower, thats how it resists knock. Timing control on these engines are done by the PCM. The PCM has no way to monitor "knock" or that you dumped higher octane fuel in the tank, therefore it cannot adjust timing for any benefit. If your engine benefits from higher octane, then you have other problems like excessive carbon deposits or base engine/timing concerns. The biggest and probably only effect you will notice is having a lighter wallet.

dave1123

Most engines today are based on an 8:1 or 8.5:1 compression ratio. 87 octane is within the PCM's control parameters, so any higher octane is wasted making the exhaust manifolds and pipes hot, not producing power. 10:1 ratio requires 91 octane and 12:1 would require 94 or better. There are discount gas stations out there who sell 84, but that stuff doesn't run well unless you've got a model T Ford.

po0dingles

I found out what happened. I searched another forum and got this:

http://www.jeepsunlimited.com/forums...d.php?t=398379

xtetra

Locally I have been able to get ethanol free 93 octane which keeps the 02 sensor and CEL happy, or seems to anyway. Some days, regardless of weather and doing the same drive I always do the engine just smells hotter when I stop. (Temp gauge reads the same as usual) Could it be because I am running 93 octane?

Will have to pay attention to the difference.

dave1123

I always looked at it this way; If higher octane makes the fuel burn slower, it's not burning completely in the chamber and finishes burning in the exhaust manifold and pipes (and converter). This is especially true with a rich mixture. Mixtures today are computer controlled to maximize power and control unburnt fuel from blowing out the exhaust. It just seems to me wasteful to use an octane rating higher than necessary to control detonation (ping).

But, everyone has their own opinion, so do whatever blows up your skirt.

I have used 84 in a carbeurated Chevy V8 with 8.5:1 compression and it pinged. After I knocked the spark advance back enough to control the detonation, it had no power. I had to use 87 at the minimum.