I do 23,400/year JUST for work. :( And another 3,000 or so for trips/meets.

Annually, I probably spend $300 more than I would for 87. And a lot less if I used 89.

The person I purchased my 90 from is a mechanic and currently owns a 97 ssei.
I asked him about the fuel question,
he runs regular and every 3rd tank puts the "good" stuff...

He reports no issues.. so he kind of mixes it up.
If my next car ran on 91 ,, it will stay with 91..

ehh... The extra $2-4 a fill up does not bug me one bit.. so 93 it is.

The Extra $2.94 per Gal i paid yesterday wasn't that bad either for what i got


100 octane racing fuel FTW.... Only $5.99gal. $38 for 6.3gal lol

The computers in our cars have two octane tables. A high octane and a low octane. As your car'* knock sensors pick up detonation the car reduces timing based on these tables until it no longer has detonation (knock). Over time if you use 87 or 89 or 91 your PCM'* learned timing tables migrate towards the low octane table and the car runs fine but with lower timing and thus less power and performance.

If you consistantly run higher grade gas (93-94) your timing tables migrate towards the max timing high octane tables and your performance (and horsepower) picks up. Every degree of timing in our cars is like 2-3 horsepower in a normal to moderately modded 3800 or as much as 8-10 horsepower in a highly modded 3800. When your horsepower to weight ratio goes up your mileage gets better (as long as you stay out of the throttle).

As a side note the car can only pull so much timing and if you consistantly run bad gas in the car you could theoretically find yourself in a position where you continue to knock (high load, hot weather conditions) and the computer can't save the motor from excessive knock and piston failure (among other things) can happen.

How long, typically, could it take for the PCM to migrate towards the higher tables if a car that needs premium has been using regular for a very long time (say...years)?

And would draining the PCM and letting it relearn help the issue?

It is a constant process so I would say within a few hundred miles for sure. A lot depends on how you drive the car. You can reset fuel trims by disconnecting the battery for an hour or so but i'm not sure it resets timing tables.

Ok, just wondering. I figured 100 miles would be long enough. I use 93 all the time but I have no idea if the previous owner used premium for the 4 years she had it. You just never know. I do know the owner was female, so hopefully it was one who read the manual.