i have always run mid-grade gas 89 octane and with the purchase of the SCT tuner i decided i would use the 87 octane setting and buy the cheaper gas! I HATE IT> the truck feels sluggish. anyone else have experince or opinion on that? cheap gas with the 93 octane setting caused a pinging in the motor when i get on it. so i changed it to the lower tune. when i got the SCT i tuned it ofr the "preimum" gas as i like the power. i hate the price of the gas!!

i have always used the 89 octane ever since i bought the truck. if i used the 87 octane i would get a CEL and without a reader i could not tell you what the code was but it would go away when i filled back up with the 89 octane.

anyway what octane gas do you run with your SCT tuner?

 

I ran each of them in various ways- 87 w/87, 91 w/91, 93 w/93, 87 w/93,91, ect....

The best run for my rig is the 91 tune with 93 octane.. I'm thinking this is mostly because terrible gas available.. I could run rec gas @ 93 with zero octane and pretty clean, as there is a boat dock within a mile of my home. The gains I saw with that weren't that much better than the 93 as it was..

I found the 93 to be thirsty.. really thirsty.. The 87 didn't feel that much better than the stock tune (w/death flash at that), and it was really hard to stay there when I knew the 91 and 93 were a ten second tune away (and along with it substantial power increase)..

91 tune and 93 gas gives me the best running engine w/ the best mileage.. Just my .02.

 

The user manual says to use 87 octane.
If you get spark knock then you need to increase the octane to 89 or 91/93 until you find one that will eliminate the knock.
The higher the octane, the better its resistance to spark knock.

You might want to check your PCV valve because oil in the cylinders causes spark knock and a bad PCV valve will let a good amount of oil into the intake manifold.
I'm thinking you already fixed the plenum gasket, that's why I say to check the PCV valve. If you replace it then you should get one from the dealership. The aftermarket PCV valves are crap compared to the Mopar ones.

 

He has not fixed the plenum. Until he does so, the OP is wasting his time and money worrying about what gas to use and what setting on the SCT to use. As that will all change after it's fixed along with new o2 and cat checked .

 

good observation Zman.. it flew right past me..

 

yes sir i do HAVE TO FIX my plenum. im waiting on the parts now. i really just wanted to see what others are doing.

 

If your truck didn't require two temperature sensors, I would sell you my old keg for about the same as what the Hughes kit sells for.. it's from an '02 though, so it only has the one tap.. It has the plate already on it.

 

How does ethanol cause spark knock when ethanol has a higher octane rating than pump gas and you say yourself that the octane rating is the resistance to detonation?

 

gas doesn't burn.. gas fumes burn.. gas turns to fumes really easy though, but at a higher temperature than alcohol..

flash point is defined as "the lowest temperature at which the vapor of a combustible liquid can be ignited in air".. the flash point of Alcohol (in gas form) is lower than gas (or gas fumes), and is therefor ignited easier than gas.

You'd have to add octane (or similar chemical that works with alcohol) to alcohol to the point it could no longer be considered just alcohol any longer to achieve near the same flash point as gas.

Octane, absolutely stabilizes gasoline to where it will ignite a much more predictable point.. it is inert.. it doesn't go BOOM by itself, it just keeps the gas from going BOOM before spark is applied..

Hopefully it doesn't go BOOM before the spark has been applied, and before the piston has arrived at TDC.. if it does, it resists the force of the crank, and something has to give.. It results in a PING.. which is most often the piston rod cap slapping against the crank and widening the slight gap that exists there.

These guys who run 85 or flexfuel also run engines that are silly retarded in timing (the piston is heading south already when the spark applies)... this keeps them from pinging, but at a cost of power..

sorry for the rant.. I was bored...

 

Ethanol actually helps to reduce knocking. You are indeed correct, Ethanol is attacked by a TON of people for being bad for engines, environment, and your wallet. These people try and spread this around to give Ethanol a bad name. I personally don't think that in its current form that Ethanol is the cats Rear to our problems, but its a step.

My state has been using a 10% blend in all of it's gas sold for over 15+ years and you don't hear of it being a major problem.

BTW. does anyone know the octane rating of e-85?