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Discussion Starter · #1 ·
Most of the time I use 93 Octane fuel in my Accent 2000 1.5 SOHC engine and gave a better performance , but recently used 87 Octane fuel and i felt a drop in my pulling power, but later after i finished the tank of 87 fuel i filled up with 93 and still see a slugish performance. I heard that when you use lower octane fuel and if the car knoks to reduce the damage the ECU automaticaly retard the engine to a low performance setting, do you think my car is still in the low performance level?? how offten these ECU learn about new settings Pls help any ideas??
 

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It's not necessarily a low-performance setting, it just retards the timing to reduce detonation (a.k.a. "knock"). Knock sensors in the engine block literally "hear" the specific sound frequency created by knock, and produce a corresponding voltage via piezoelectric crystal, sending that voltage to the PCM. The PCM immediately reduces the timing with KR (Knock Retard) timing signals that are read in actual degrees of timing, and does this until it no longer receives knock-induced voltage from the knock sensors.

It may take a little bit, maybe 50 miles or so at various speeds and driving conditions, or a certain number of full driving cycles (warmed up to operating temp., then fully cooled) with no Knock Sensor signals for the Accent's ECU to respond and increase timing again. I know that the PCM (basically an ECU) in my Buick makes timing changes immediately, and can change the timing very slightly at different RPM's, and change it back immediately. I don't know the Accent's ECU enough, though...maybe someone will chime in that knows the internals a bit better. Hope I explained it well though!
 

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Most of the time I use 93 Octane fuel in my Accent 2000 1.5 SOHC engine and gave a better performance , but recently used 87 Octane fuel and i felt a drop in my pulling power, but later after i finished the tank of 87 fuel i filled up with 93 and still see a slugish performance. I heard that when you use lower octane fuel and if the car knoks to reduce the damage the ECU automaticaly retard the engine to a low performance setting, do you think my car is still in the low performance level?? how offten these ECU learn about new settings Pls help any ideas??
Unless you are boosted (turbo, supercharger, nitrous), you are wasing money using higher than 87 octane in your Hyundai. ALL Hyundai cars are designed to run on 87 octane.



You get ZERO gain in performance and mileage when using higher that 87 octane [(R+M)/2] fuel unless your computer was designed to do so. The factory Hyundai computer doesn't have the ability to advance the timing by itself, this is why higher octane doesn't help. If you did have it reprogramed to take advantage of the higher octane then it would get better performance and mileage.

Read here:
Regular or Premium? - Feature / Features/Classic Cars / High Performance / Hot Lists / Reviews / Car and Driver - Car And Driver
ABC News: '20/20' Takes on Summertime Myths
Minnesota Commerce : Gasoline Octane Facts
FuelFrugal.com - Money Saving Gas Tips - Gas Saving Myths
Save Money On Gas - The Octane Factor

The only way to get a performance/mileage improvement with higher octane (without internal engine) is to reprogram the factory fuel and ignition maps in the stock computer with a fuel/ignition tuner.

If you are getting better performance on higher octane fuel then there is a problem with your engine that needs to be fixed. The higher octane fuel is only masking the problem and just giving you back the performance you would normally get on 87 octane of the engine was operating properly. So if that's the case, get the engine checked out and repaired.

Either way, you are throwing away money using higher than 87 octane.
 

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^^^I was gonna say that, but I got so wrapped up in answering his actual question that I completely forgot...lol. Duh!

But yeah, don't waste your money on Premium.
 

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explain why then when i filled up with ultimate 98 in australia (as opposed to normal 91) and same driving, i got an extra 70 kays out of the tank....
(sohc x3)
 

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Better detergents, better base stocks, and pure old fashioned placebo effect. 70km's is well within the realm of traffic and signal noise to tell how your fuel consumption is.

The best octane to use for your engine, or any engine, is the lowest that will not cause detonation. Period. And for good reason, its in the construction of the fuel itself. Octane is a measure of how fast a given fuel burns, the higher the number the slower the burn. The slower the burn, the less likely the fuel is to ignite itself under high cylinder pressures or due to hot spots in the combustion chamber (i.e. detonation). This is good if you can take advantage of this with higher compression, advance ignition timing, lots of boost, etc, not so good with a stock motor with no tuning available. If you can't, you just have a slower burning fuel thats going to make less power.
 

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Discussion Starter · #7 ·
Basically you guys are tellin our Accent's doesnt have the intelligence to adapt to new fuel conditions?? and sometimes using higher octane may decrease power :confused:
 

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Basically you guys are tellin our Accent's doesnt have the intelligence to adapt to new fuel conditions?? and sometimes using higher octane may decrease power :confused:
No. The spark and fuel tune that are loaded into your stock ecm was built around 87ish octane. Putting in higher octane won't advance it's timing.

The only people that will "see extra power" are cars with ecm's that where programed around 93ish. They really are not seeing "extra power" they are finally making what they where intended to make. Just like our accents they run normal until they hear knock. That knock is caused by running a lower grade fuel than what the fuel/spark maps where made for... they go back and put 93 in and timing comes back to normal.

The accent has no way to know what octane is in the tank until it starts to knock. Then it pulls back timing until the knock goes away. Taking hp and fuel mileage with it. It is not that the accent isn't smart enough, it is hyundai being bright enough to know its customer base doesn't want to pay the extra money for higher octane. If you could find gas lower than 85/87 the accent would pull timing just like everything else.

hell - id rather run a poofteenth less power in the pursuit of more kays a tank...
Maybe you get more mpg out of a tank of premium because of the dint it put in your pocket book is tugging on your right foot? Not letting it go down as far or as fast?!.
 

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The power thing is an interesting little side track... The accent's ECU certainly does not have the intelligence to adapt to different octane fuels, however that is not the entire story when it comes to making power.

There has been a lot of stink raised recently in SCCA racing classes about requiring spec fuels or mandating that all fuel for race cars be bought at the track. Why? Because some of the high-zoot specially formulated race fuels can and will make more power at a given octane rating than other fuels. Maybe 3-5 hp more, at a cost of $30-60/gal (or less depending on who you know and who your race team is), but thats due to a different formulation of th additives in the fuel and to tuning of the car's fuel injection or carburetor and ignition settings. The real bitch comes in the fact that the only way to know for sure is to buy the damn race gas and dyno the car. Every car is going to respond differently to different octane levels and additive packages. Higher octane fuels also burn dirtier, which lead to deposits and caused problems on those cars. Thats why higher octane fuels have so many detergents and other cleaning agents, to clean up the crap left burning the "better" stuff.


A real ironic twist on this are the old IMSA RX-7's from the early 80's. The 12a rotary ran great on the shittiest gas you could give it, naturally aspirated that particular motor was particularly resistant to detonation. The race teams actually had to bring their own 85 and 87 octane to the track to get the cars to run their best!

Usherly - Doing the math here, the difference between using regular and premium, even with the extra 43miles per tank (70km's), works out to about $0.001 per mile in favor of premium gas. A 10.5 gallon fillup on regular was about $33.08, on premium $35.60. Range would have been about 300 miles in my LC, 343 miles hypothetically with your +70km/tank gain in mileage. The difference between 28mpg and 32mpg, approximately, is almost nil with the cost difference between the two fuels ($3.15 for regular, $3.39 for premium on my way home today). For me in America, it probably doesn't matter. For you in Australia, where the price spread is the same (I think?) but you're paying by the litre, its definitely more noticeable but skewed in favor of buying regular gas over premium (~4L per gallon means my $.24 spread per gallon is more like $1per gallon down there, making premium the more expensive choice in terms of $/gal).
 

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Heh heh, yeah pretty much.

Basically you guys are tellin our Accent's doesnt have the intelligence to adapt to new fuel conditions?? and sometimes using higher octane may decrease power :confused:
 
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