Gas situation.. need your thought.

[Conga1991]

So just moved down to Arizona. My Dad decided to fill up my tank, thinking that he knew I use Premium, but puts Unleaded in. I have a 7mgte by the way, pretty much stock besides fmic and exhaust. Would running that kind of gas until its used up be bad for my engine?? I haven't noticed a difference while driving it other then I'm getting much better gas mileage, hopefully its not running lean ): I dont have an A/F sensor/gauge so I wont be able to find out. Just want your thoughts if running this gas is bad or not?

[cre]

Different gas grades aren't going to affect your A/R at all. Lower octane fuel has more kinetic energy and is less stable... You'll most likely see better mileage (as with most older cars) and slightly less power. As for options: 1) baby it until it's empty 2) add two to three gallons of Toluene (available at Home Depot, Lowe's, Ace) to significantly raise the octane.... You'll still need to baby it until it has time to thoroughly mix in.

[Conga1991]

Cre! You've done it again, like always!! The Guru for answering almost every question presented on here! When putting the additive to the tank should I put some premium gas in it to help dilute it? or should it be fine by just adding it in without adding gas?

Thank you in advance!!

[cre]

You're not going to be able to get enough premium in there with a tank already full of regular and a couple gallons of toluene. Don't worry about topping it off if it's already quite full. Actually, it'll mix better if there's a little room for it to splash around. Worst case scenario is that you end up running 105 octane for a a couple hundred miles.

How much fuel is in the tank? I had assumed 3/4 or more. If it's less you'll want to adjust how much toluene you add accordingly.

[Conga1991]

Bringing this post back up from the dead. You said that with lower octane gas raises mpg. if I use Unleaded gas and mix with toluene will that still improve my mpg or will it be the same as if using premium gas??

I am currently using premium and im not even getting around 20mpg. I mainly drive in town and only use the freeway for less then 10 mins a day to get to school.

What are some ways to improve my mpg?? I am using used stock injectors that have about 180k on them, upgraded fuel pump to walbro 255, upgraded turbo to 57 trim, driftmotion intercooler set-up, and 3.5 inch exhaust with ddp. Not sure if this can be the cause but whenever I hit WOT in 3rd or higher I hit fuel cut, doesnt happen in 1st or 2nd though. cel comes on and its the knock sensor or the wiring, pretty sure. Hope this helps and whoever can give their .2 it is greatly appreciated!

[cre]

I'll post more later. But for now, general rule of thumb: Higher octane = less energy... It has less kinetic energy, not to be confused with the engine's being able to make power. Ideally, as I've said before, you want to run the lowest octane possible for your setup with the least amount of ping. Running 105 octane fuel on a stock 7M-GE will result in terrible mileage and even worse performance.

It's a balancing act and there's no simple cheat beyond keeping combustion chamber temps down (Ceramic coated air ducts, good IC, air filter not in the engine bay, EGR system intact, coasting with the clutch out, water/meth injection) and then run only the octane you need. I live a mile higher than sea level... I've run 87 octane on a few higher rated vehicles and found more response with no discernible difference in the data logs as far as the ECU adding or pulling timing.... Now going from a recommended 93 to 89 or 87 is something that's safe here due to the altitude and you can find publications by various manufacturers and oil companies stating what octane to use for a given altitude. Factory recommendations assume sea level. Many newer vehicles are better able to ride that performance threshold though and are able to make good power while maintaining equal mileage in which case I'd suggest sticking with premium if you can afford it.... but the MKIII isn't that smart. Normally I still run 91 octane (or 89 when I can find it. 91, 87 and 85 are the common ones here) as it's cheap insurance and I'm not trying to squeeze every bit of performance or mileage out of my car.

A code 52 will SLAUGHTER your mileage! Fix it ASAP.

Seriously though, your mileage doesn't sound off to me at all. I don't know how your driving style is but city is always the worst.

Do you have any means of fuel management installed? If not, add that and tuning to the list.