Yeah... so.. I just buy the cheapest gas I can find.. But in the 4.0 does the grade of gas make a difference with how it runs? My answer would be maybe a little, but not really... what are your thoughts on this?

 

I have experimented with the different grades on mine. Any differences were not worth the extra cost of the higher grades. It ran the same on all grades, did see .5-1 mpg improvements with mid and premium, but at plus .10to.30 $PG price difference, low grades are more economical. I do not use cheap gas, always purchase from major suppliers.

 

With my 94 4.0 if I buy the lowest grade I get a decent amount of pre-detonation. The middle grade makes it go away nearly completely.

 

I use the 87 octane in mine and it runs perfectly fine. If it was stroked maybe I would use a better grade in it

 

Really the only time you need to go to a higher grade gas is when you experience "knocking" . This is when the compression of the air-fuel mixture in the cylinder ignites (due to compression and the heat of the engine) before the spark plug ignites it. Generally in newer engines you have a higher compression and hence a need for a higher octane fuel. If your curious about it, google "octane" and/or "engine knocking" , there are tons of articles written on these topics.

Edit: But as A1 said, 87 aught to be fine.