READ YOUR MANUAL: AKI makes a big difference...
Feb 02 '00 (Updated Aug 18 '00)
I used to be under the assumption that the higher the AKI (octane), the better the fuel. I used to automatically fill up on the most expensive juice I could find thinking that it would really make a difference in my old beat up 1991 Ford Escort LX Wagon grocerygetter. My placebo buttmeter told me that I had more power and the pickup was better. In reality, I was just wasting money.
About a year and a half ago I bought a new Subaru Impreza with a 2.2L boxer flat four banger. Again, I was under the assumption that I should buy the best fuel with the highest AKI possible. Again, I would have been wasting my money. After reading the manual (you have read the manual to your car, right?) I found out that 87 AKI (regular) fuel is required in my particular engine, otherwise it will knock and ping.
Over the past year and a half, I've plotted every single fuel stop and service to keep an accurate record of my mileage and performance. That chart has revealed some surprising things. The most notable is that the three or four times I experimented with 94 AKI fuel, my gas mileage went down by 2 MPG. I also noted that although my engine had a lot more power, it had also developed a case of the knock and ping syndrome.
The ECU (computer) in the car was tuned specifically for 87 AKI and, when it encountered the higher octane, got confused and didn't manage fuel properly. After talking to my dealer, they said said that using a higher octane than the ECU is tuned for can actually damage the engine in the long term. Not a happy thought...
So, remember to check your manual for the proper AKI to use. They way I look at it is that if a car company with hundreds of thousands of man hours in research tells me to use regular fuel, who am I to decide that I need premium? So, unless you're driving a performance turbo or supercharged engine, stick with what the manual says.
On a side note... If you insist on running premium fuel, stick with it. Switching between premium and regular will confuse the ECU as it tries to compensate between the two octane blends. Also, doing an ECU reset might help the fuel management system "accept" the higher octane. Since dealers don't want consumers to know they can reset the ECU, you'll need to find a group of enthusiasts to help you with the procedure (each car is a little different, but usually involves disconnecting the battery for 8 hours, reconnect, start the car, idle for 30 minutes and then drive at highway speeds for 30 minutes).
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Epinions.com ID:
hamors
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Member: Sean Sosik-Hamor
Location: Pelham, NH USA
Reviews written: 21
Trusted by: 37 members
About Me:
Sean is a technology and motorsports enthusiast as well as a driver for Trunkmonkey Racing.
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