Premium in the minivan.. don't think it likes it.
 

Hi folks,

So due to some weird chance, I ended up with a full tank of premium, 91 octane. I pulled up at the pump on empty and there was a sign on the pump "Out of regular, use premium at same price" and there was a maintenance crew there, looked like they were having some problem with the tanks or something... so I thought, "what the hell, I guess it's getting premium..." and filled up...

Driven a few trips, and the minivan doesn't seem to be liking it much, seem to have lost low end, and need to give it more pedal to get moving. It does sound a little smoother though. Kinda like with acetone, but without the get up and go. It seemed to improve a little the first couple of times I started it, but guess that was all the ECU trim could do and it's still not great. It likes midgrade 89 octane, to the tune of 5% more mileage, but since it's usually more than a 5% cost difference I use 87.

So I'm looking around for something to stick in it to drop the octane, might go with a litre of varsol and a couple of oz of 2 stroke oil. Figure it will probably clean it out while it's at it. Then I guess if it still feels sluggish I'll top it up with 87 when I've run a bit out. I guess I could advance the timing, but that's a PITA, and I'll have to set it back again next tank....

Road Warrior

Strange, our premium is 93...

But I will say this much:
With MOST fuel injected vehicles, the best grade of fuel for it is what the computer was tuned to use... So if for example your van was tuned for 87 octane then that would be the fuel that would likely result in the best performance (and FE).

The only way I know of to get around this is to have the computer re-programmed (to something like a stage-1 chip), neither a cheap nor an easy to do option.

Good luck

It varies by brand here, this one is 91, others are 93 or 94...

Yah okay I see... At least my experience has been with my Dodge which is apparently tuned for 87, any grade but 87 doesn't really do much for the truck... And in some ways much like yourself it almost seems like it hurts (thou I couldn't say for sure but the extra I have to pay at the pump sure don't help LOL).

The one other thing I did notice too thou, you might want to run 3-4 tanks full through it... The benefits of premium aren't always apparent on the first tank, but don't come yelling at me if after 15 tanks it still hasn't improved hehe

I did, I ran more than a few tanks through on my truck...
But in the end I went back to 87, it just wasn't showing me any benefit, none at all.

One way to find out is read your Owner's manual, some tell you what fuel to put in it, that is a fair indicator as to this tuning issue.

maybe its not just the octane. perhaps the station had a problem like water getting into fuel, and thought it was only affecting the regular grade, but maybe it was affecting all their fuels. maybe u got a lil extra water, or random contaminant.

ya cuz octane DOES NOTHING on a low compression engine if you go low enough you could run the car of pretty much anything that burns (hence during the 1930's depression theres story's of people running thier old cars off of moonshine)

The octane ratings are there so if you have a high compression engine (gets more power out of it) sometimes just the heat from the combustion chamber and the amount of compression is enough to actually ignite the mix without a spark plug firing, higher octanes don't ignite when compressed the same amount.

so whats that mean: it means if your car calls for regular then you can use regular- race fuel with no harm or performance drop or gain.

if your car calls for midgrade you can only use midgrade-racefuel cannout use regular because its octane is probably too low.

and obviously if your car calls for premium then you must use premium or race fuel...


so im betting you got water in it or rust particles, etc. BTW next time you see a station that is having repairs to the tanks or pumps DO NOT GO THERE...

Don't think it's got water in because it's not stumbling. I was thinking that 91 had a few thousand less BTU than 87 though.

I agree with 2000mc. If you really are experiencing reduced performance, the gas is defective or contaminated. Under no circumstance should increased octane cause decreased performance/economy.

Your high octane observation may hold true for the acetone yall seem to be testing. Maybe you will need a few tanks before the computer can fully adjust to the acetone?

im not positive, but i also thought that 91 octane had fewer BTU than 87 octane. however, i was thinking that the difference is only a percent or 2, nothing you should be able to feel.