My car was custom tuned last year for 93 at the same time I had a cam installed. A few weeks ago I took the car on a longish trip and ended up in an area I've never been to before and needing gas.

I typically try to run the same fuel in the car, just for consistency's sake, and that is usually Sunoco. Well after driving around with the Low Fuel light on for a while, I hadn't see one, and I figured I only had a few miles left, so I just pulled into the first station I could find.

This station only sold 87. So, I put a couple gallons in there just to get me to somewhere that I can get some real gas in there. I never got any predet or anything, and I can't really say the car was down on power, since I babied it around just for this reason. Instead of going to the first place I saw and filling up on 93, I decided to run the 87 basically till empty to get it all out of the system before I put 93 back in.

Now though, the car definitely seems down on power, and either someone accidentially hit the trip reset (which would have to be me, since nobody else drives it) or I'm getting about 9 miles to the gallon now. I'm not on my 2nd tank of the usual 93 since the tank of 87.

Do I need a retune?

 

You might be using the low octane table now since you were using 87 octane. Over time it will go back to the high octane table if it doesn't get anymore knock retard.

Do a few WOT runs over a few days and that will help it get back to the high octane table faster, as long as you have real 91-93 in the tank and no real knock retard going on.

 

You should be OK.

Bill