ok when i picked up my truck i asked the guy if i needed to run premium, and he said no. I told him that was BS and that in all LQ9's they strongly reccomed 91 octane or higher. he said that when they fill up all new vehicles regardless of motor they use 87. so i drove the truck about 250 miles and then filled up with 92. my question is when i put the tank of premium in i can't get a reading of over 10.8 MPG, but when the tank had 87 in it i was pulling around 13.9. is the pcm reprogramming itself for the higher octane or am i really loosing milage my runnin 92?

 

What do you expect? why should they spend anymore money than they have to?

Who did you buy your 92 octane from? Citgo? I hope not, but it would make sense (from my experiences)

 

There are a couple reasons why your display is showing less MPG. First of all, the MPG calculator is not very accurate. If you want to accurately measure your MPG, you have to record your truck's mileage and how many gallons you put in your tank at EVERY fill-up. Find the difference between your previous fill-up mileage and current fill-up mileage. Take the gallons you just put in your truck and divide it into the mileage difference. I do this everytime I fill-up. Are you driving the same way now compared to when you had 87 in the tank? Are you driving in the city more instead of the highway? If you don't care about the extra cost, I would run premium all the time. I'm positive the owner's manual recommends 91+ octane for the LQ9.

 

Start putting 93 or whatever is the best stuff you can get in it. Get used to the price. You're gonna need it when you get a custom tune anyway I got 12mpg with the 5.3. After I get the 6L tuned right I will see what a diff. that makes. I run 93 all the time. 26 gallons=300 or so miles.

 

i do calculate all of my milage by hand, i was just using the guage as a reference. actual math by gallons gives me an even 10MPG. 92 is the best i can get around here and i intend to use that. i purchase it from the BP around the corner.

Would the difference in octane cause a variance in MPG? And does the PCM need time to recalibrate for a higher octane?

 

Yes, there are dual tunes in the LQ9 PCM's for the lower octanes. So you put in the 87 and it adjusts running parameters to basically prevent knock.

 

Premium is usually 30 cents higher than reg.... so lets say you fill up 10 gals. .30 x 10 so... its like 3 bucks more your paying.. not that big of a deal...

and if your empty or close to it... 25 gals... 25 x .30 $7.50 more than reg. Idk, i spend so much in gas i guess i dont care anymore.

 

Im used to $50 a week.

 

thank you for the reponse to one of my questions. how long does it take for the pcm to "reconize" the higher octane and adjust it self?

 

I think it's really based on knock. So it it starts to sense it, it adjusts, if it's not getting knock it'll try the higher octane settings. That's just how I think it works though, not 100% positive.