Does computer know what octane you're running?

OK, it's my Buick Enclave, but I have a question. I stopped for gas a couple days ago and the station only had premium (selling at regular price). I filled up and had problems starting the car.... it wouldn't pop right off as usual, after it started everything was OK. This would happen about 75% of the time. I have since used that tank and back to regular gas and it starts right up. Does the computer "know" what octane you're using and try to retune the engine? That tank of gas was the only time it acted up in 80,000 plus miles.

In your case, I doubt the fresh gas would have instantly been in the injectors at the start. I'm guessing that you didn't coast in there totally empty, right?

Higher octane fuel lights off at a higher temperature. This could explain the difference...

The computer has short and long term fuel trim (tweaks to the original fuel mapping that are unique to your car).
It also should have knock sensors that often are used to optimize timing curves that would be more likely to be affected by octane. It doesn't "know" it's different gas, just that it is more resistant to detonation.
I'd guess that it's as said, just slightly harder to light off.
May also be a warning to do a fuel filter if it's got a bunch of miles on it.

Today's gas goes stale quicker than it did. Might have been a tankful of stale gas they were getting rid of with a story.

You could try another tankful of premium from another source to see.

My '97 Mustang GT runs on anything, but its computer adjusts timing for detonation. Seems a bit perkier on 92 than 87, but never had a problem starting it.

I'm not aware of sensors that read octane, but there must be SOMETHING that the computer reads to know the difference in E10 and E85 to automatically adjust the tune. Supposedly "perfect stoich" of ethanol is not 14.7:1 like regular gas so the computer can't read JUST the O2 sensors, can it?

And not all cars have knock sensors...

I'd guess it was just a tank of bad gas. Want to test your theory? Get premium gas from another station... Chances of getting 2 tanks of bad gas from 2 different stores "back to back" is very slim.

Yeah, I should have said detonation, and I've edited that.

Quote:

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I'm not aware of sensors that read octane, but there must be SOMETHING that the computer reads to know the difference in E10 and E85 to automatically adjust the tune. Supposedly "perfect stoich" of ethanol is not 14.7:1 like regular gas so the computer can't read JUST the O2 sensors, can it?

And not all cars have knock sensors...

I'd guess it was just a tank of bad gas. Want to test your theory? Get premium gas from another station... Chances of getting 2 tanks of bad gas from 2 different stores "back to back" is very slim.

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Tom,

Fuel sensors are on every flex fuel vehicle.
There are even DTCs for them.
P0169, P0176, P0177, P0178, P0179.
Also, since as you say the A/F ratio is different for gas, alky and any blend, when in feedback (operating temp, not WOT or decel, O2 providing results), it can 'see' that it's too rich or lean and compensate, although that's not 100% and not all the time. O2 feedback is better used to trim or adjust the programmed ratio, not make broad changes. Gasoline is 14.7:1, alky is 5.0-6.0:1.
These are by weight too!

More at http://www.smokemup.com/tech/fuels.php

Not all cars have knock sensors, but GM LOVES 'em and I guessed that any Buick Enclave (2008-present)
http://www.edmunds.com/buick/enclave/
Is going to have 'em.
Ford loves to 'test' theirs by purposely overadvancing the timing on acceleration and using the knock sensors to pull timing out.

and I agree on the bad load...