My manual says that it's ok to use 87 octane, tho the speedo says "premium unleaded only". From what I've been reading, the PCM adjusts the timing (either advancing or retarding) depending on gasoline octane. I guess it looks for light spark knock which "doesn't harm the engine", and retards the timing. I'd imagine the engine is very conservatively tuned, so even bad gas would be ok to use. You'd probably suffer in gas mileage tho.

 

So, Quick Trip advertises that all their grades of gasoline are TOP TIER gauranteed gasoline(another TOP TIER gasoline is Chevron... if you don't know what it is just Google it). I have been using their premium 91 octane just like the owners manual says to but I've noticed that many of thier stations around Des Moines, IA have their Mid-Grade gas specd at 90 octane with a 10% ethanol mixture. Has anybody ran this gas or a similar gas with an 90 octane rating? Just curious if this might be ok. It would save alot of money in gas but if there is a chance it could cause knock/timing to be retarded/damage engine I won't even try it. Anybody?

If the mixture is Octane 90 + ethanol, then the octane rating would be around 94 which is good. Ethanol increases the rating, with 87 octane and 10 % ethanol, you're at 93.

If the overall octane is 90 (including the ethanol), then the only problem you'll have is reduced performance. We can run fine with 87, the computer adjusts to it.