Forgive my ignorance, but I've got a question as to what all is included in the 'tune up'. It is my understanding that the engine constantly tunes itself to the conditions as that's pretty much the glory of the i-VTEC system and the ability to advance/retard the cam timing. Besides replacing spark plugs, is there any mechanical/computer timing adjustment that is done?

I ask this because about a week ago I went to fill up my 04 6MT but the station was out of the 92 octane. So, I got the 89 octane instead. I had about an 1/8th of a tank left that was 92...and since I've never put anything under 92 in my car I thought I'd give it a go. Well, after adding the 89 and driving a bit I noticed that the car accelerated much smoother and felt like it had a bit more power...and I've noticed an increase in MPG . I know that goes against the whole idea of a lower octane fuel, but was wondering that if the lower octane changed the timing of the engine to run a bit more efficient? I'm pretty much at 100k miles which is around the time for a tune up and wondering if something was causing my car to run with a bit of an advanced timing - and the slightly lower octane retarded it a bit?

Anybody have any experience with this? Thanks!

 

Don't know about 92, the highest I can find in CA is 91. A few weeks ago, I put in 89 once, about 3 gallons. At that time there was only about 2 gallons 91 left in my tank. (The fuel meter was pointing at the lowest.) I drove 60 miles and fill up the tank with 91. I didn't feel any different during that 60 miles of freeway driving.

Oh, my TSX is 2004 AT with 94200 miles on it.

 

Really??? Premium fuel over here is 93 octane....

 

yeah the tree hugger states use ethanol about 10%. This drops the octance rating. Highest in CO is 91 also.

 

Gas stations have two tanks...one for 87 and one for 91 (or whatever octane your state lets you have). They mix the two in varying amounts to get the middle octane. If they were out of premium, how did they mix it to give you the middle one?

Cars have a computer chip that controls the engine...it's called the ECU. It takes readings from several sensors and makes adjustments. It can advance/retard the timing if necessary.

VTEC engines have two cams...one for lower RPM's and the other for higher RPM's. Engines can be tuned to be good at low speeds but horrible at high speeds, and vice versa. By having a cam for each, the engine can switch over when needed.

Higher octane means that the fuel is harder to burn. Thus, higher octane fuels won't pre-ignite. If I had to guess, your ECU was still tuned to 92 octane (it usually takes 1 or 2 fill-up's for it to adjust fully I think). Now that it has lower octane in it, the fuel burns a little earlier than expected, allowing it to burn more fully (ie: the result is similar to advancing the timing). Since they were out of 92, they probably gave you 87.

Also, if it was a gas company that you don't usually frequent, you might have experienced better performance. But that's another story.

human668, you either moved into town recently, or you just started driving. Cali used to have 92 octane, but they reduced it to 91 octane about 7 years ago. They were phasing out a fuel additive (MTBE?) for environmental reasons, and they were charging royalty fees on the formula for 92 octane that didn't have problems linked to MTBE. Thus, they just decided to phase it out.

There's a reason why alot of other states have 93 octane or above, and it's mostly due to demand. There's good oil and bad oil...they're mixed together to make gasoline. You need the good stuff to make higher octane fuel. If you allocate the good stuff to make more premium fuel, you'll have too much of the bad stuff that you can only make octane that's less than 87. If the demand for premium fuel in an area is low, they can provide higher octane because not many people will buy it. In California, home to the automotive world, everyone wants the higher octane fuels. Instead of using a higher percentage of the good stuff to make 93+ octane, they can use a lower percentage and make 91 octane. Thus, they can make more quantity of 91 octane than if they were to make 93 octane.

 

Ethanol is added to increase octane. It resists pre-detonation, thus the octane rating of the fuel is increased. Racing fuels have lots of ethanol.

 

You are right. I was still in Hong Kong 7 years ago and I was too young to drive. At that time I never thought about I would drive a TSX. My mum is still driving her 97 Civic in Hong Kong. I was surprised by the low gasoline price in US. I knew it's cheaper than Hong Kong but 1.69/gal really got me attention.

Since TSX runs fine with 91, I have a silly idea. For thous who can get 93. Why not mixing 93 and 89 on your own to save some money

 

Some people do do that. Some also do 89 and 91 so that they can save a few cents while not suffering too much in performance.

 

Fu(k it just fill her up with turbo blue lol


"In the fast disclaimers voice" (i take no responsibility for any damage to your car)

 

thats interesting because ethanol has less energy thus less mileage. About 1/4 if I remember right. Thats why buying pure ethanol is a scam, at least at current prices.

2.5 ethanol-less energy less mileage
3.00 for gas-better mileage, better price