billcarr

I was running 87 octane gas for the first few weeks, I thought the engine was slightly rough at 2000 rpm and up hills. With gumout carb cleaner it improved. Now I'm running 91 octane and it seems better. Does any one else prefer 91 over 87 in the 4.2 ? Has any one had a bad experience with 87 in the 4.2 ? Is there a preferred brand of gasoline ? Thanks for taking the time to answer.

2007, F150, 4.2, 5 spd man, 3.30 rear grears, AC PS.

dplummer87

Personally, I never had problems with the 87, i actually got better MPG with the 87 than i did with 91 ( i was using a tuner on 87 setting always)

As far as gas goes, I think chevron or shell is "supposed" to have better gas, i think thats because of the additives they put in them. But im no gas tech guy, i dont think there is that big of diff from 87 from this guy or that guy, as long as it reads 87...Like i said, im no gas guy though. my 4.2 was an 05 STX. Flowmaster exhaust and Superchip.

Mod (Ret.)

My 2005 4.2 runs fine with 87 octane. The only time I run 91 is if I'm towing (placing a heavier load on the engine).

What "brand" are you using? I stick with Shell, Exxon, or Mobil.

Perhaps you just got a bad tank? Try another station.

billcarr

I agree wholeheartedly to the bad tank of gas idea. I have learned during this sojurn if a place sells cut rate this, they probably sell cut rate that and maintain nothing. I did change stations btw and thanks again.