Well after taking pride in the fact that I only use super unleaded in the Ram, I read the manual and it specifically states that the 5.9 should use 87 onlyand higher grades could actually hurt mileage and performance. I'll be damned.

 

I have the 5.9 and I use Premium, but that's because I have the chip {Mopar PCM}. Don't change your gas, justbuy a new PCM... hehehe! LOL! <IMG src=smileys/smiley36.gif border="0">

My manual from 94 doesn't say that though... LOL! Phew!

~Amanda <edited><editID>Dodgegirl19</editID><editDate>38018.5211342593</editDate></edited>

 

Actually, I don't think they make Mopar PCM for mine. I ordered the SuperChip programmer last week, hope it comes soon.

 

Hmmmm.... I'll look into it for you, see if I can get any info.

~Amanda

 

Thanks, I am basing that on a conversation I had with Joe and 360 Air Intakes.

 

OK.....the newbe will give his long drawn out explanation of this. Please bear with me.</P>


I was told that since my truck (99 SLT 318 w/ 5speed) had no knock sensor that using higher octane than needed would do no good and may hurt for the following reasons. Be remember that in simple terms,octane in fuel is the ability to resist burning....i.e. the higher the octane the higher the temp must be to get it to start toburn.</P>


1) Ina vehicle without a knock sensor there is only an estimation (from the computer)as to how much timing to give. Given the signals from the TPS, temp sensors, and others the computer basicaly says to itself...."I am turning 2500 RPM, with half throttle, the intake air is about 102 deg., I am in second gear, the manifold vacuum is such and such,the oxygen sensor is showing .6 VDCand the YADA...YADA...YADA, I will give the engine about 25 deg.BTDC of timing.In contrast, a knock sensored vehicle the computer takes all of these things into account as well as a reading from the knock sensor (a modified microphone).It will put more timing in until it starts to 'hear' a knock. Then it starts to retard the timing.....then it will add timing....then it will retard..... This is done several times a second. Basically the more timming you add the more power you will get. However you will just have to trust me on the reasons for this. I will go into this at a later date. Long a short of it....in a non-sensored vehicle (such as most of our Rams) if you are not trying to solve a knocking issue then the higher octane rating will do nothing but cost more at the pumps. Even with the HI-PO computers if you are not geting a ping or knock on 89 octane then going with 91 octane is doing nothing.</P>


2) Given that octane rating is the resistance to burning and the engine is cold,the computer has a few things in its program to calculate again. The ogygen sensor is not in function (needs to be at temp.) yet, the engine is at a disadvantage because of the cold fuel already has a problem burning at the calclulated rate of 87 octane fuel. Now put in 91 octane fuel and this is the cause of some early morning stumbles. It will also sent way too much fuel into the cat . converter (not good). It is already fuel loadedunder normal cold start condidtions as it is and the backfire is not good no matter how you look at it. This is a lot more obvious in my 5 speed than it is in an automatic. </P>


And, I can tell whensomeone has put fuel in my truck after borrowing it. My friends thinkthat sinceI drive it like a sports car that it will need premiumfuel. It only takes a few stumbled stop signs to figure it out I have 26 gallons of premium fuel in the tank. I have always used 89 octane fuel since new. I alway get a knock or ping with 87 octane fuel (except Chevron or 76 gas). Even after the dealer installed the updated computer that was to help the pinging issue, it isstill there. The solution as per D-C is to use 89 octane fuel in my truck. </P>


I hope this is informative and not boring. These explanations are based on what has been told to me as well at experiance.</P>


Eric</P>