just how did the STP kill the engine?? i've used it a couple of times now...

 

i used prestone FIC and for that gas tank it was good i made the best milage on a gas tank ever 360mi
I then used prestone FIC w/ octance boost like a lil later it says to do it every 3k and it killed my gas milage for that tank to 290
I average 310-330

Im guessing the octane boost didnt help much