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Sorry if this has been covered... searched.
Took a ~320 mi. trip. Before I left, I filled up with 89. There was about 1/8 tank of 91 in the tank when I filled up. At the end of the trip, the low fuel light was not yet lit, and there appeared to be about 1/10 tank left. Every other time I've made the trip (using 91-93 octane as I always do), the light has come on just as I'm arriving at my destination.
Nothing about this trip was out of the ordinary... same average speed, used the A/C most of the trip, etc.
So I'm wondering if the lower octane had anything to do with this, or whether it was just a fluke. The PCM is supposed to retard timing if lower octane is used, which would lower MPG instead of raise it. Of course, I'm not convinced the stock timing is really "optimized" for 91+ octane anyway, but that's a different story.
Anyone else encounter this?
E0 #36
'95 Ranger
'82 Honda CX500
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Lower octane is just silly, period.. though I am sure you don't want anyone to preach to you. You will get less mileage, and less power with lower than premium. Also, most people say that they don't worry about using less than premium as the computer will "simply" retard timing, etc, effectively relying on the knock sensor to not allow detonation from using an octane that is too low.
One thing about that is: you have to rely on the knock sensor. the sensor doesn't do anything until it has ALREADY detected knock/ping. Not good.
You are likely seeing headwind/tailwind.. elevation climb/elevation fall variances. unless you have performed this trip multiple times, and used premium from A to B once, then from B to A the next time, etc. (this eliminates the elevation change, temperature, humidity, pressure, and wind variances because you are using both grades in both directions...)
Simply put: you either had help (weather, elevation, etc) on one way, or you were driving slightly different in high expectations. Of note: you were likely causing damage the entire time.. joy joy!
Ray
'99 CSVT - Silver #222/276
In a constant state of blow-off euphoria.
Originally posted by Kremitthefrog:
I like to wear dresses and use binoculars to watch grandmas across the street.
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Originally posted by Ray:
Of note: you were likely causing damage the entire time.. joy joy!
Ray
All though im not recomending low octane in an svt. I seriously doubt he did any damage to his motor driving 300 miles on low octane.
98 csvt t-red.. sho-shop intake, b&m, fidanza, spec1 clutch, Torsen, DMD,optimized Y& TB, Brullen, rear strut bar,h&r's,17" konig traffik's.
"I say what I mean and I do what i say"
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You mean: "I seriously doubt he did devestating or noticeable damage"... any wear, tear, or damage, regardless of extent, is still damage, and he was likely to have caused MORE excessive damage to his engine than during a 300 mile trip with premium.
Ray
'99 CSVT - Silver #222/276
In a constant state of blow-off euphoria.
Originally posted by Kremitthefrog:
I like to wear dresses and use binoculars to watch grandmas across the street.
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so the SVT is set for premium... I didnt know that.
I can say that when I use premium, my mpg drops a tad [but it feels like the car has a bit more giddyup].
Not that I am an expert on this, but maybe your cars running really rich on premium and the lower octane is running a bit more efficient.
yes... I am a cougar owner trolling on your board.
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Originally posted by bensenvill:
so the SVT is set for premium... I didnt know that.
I can say that when I use premium, my mpg drops a tad [but it feels like the car has a bit more giddyup].
Not that I am an expert on this, but maybe your cars running really rich on premium and the lower octane is running a bit more efficient.
You're right. You're not an expert.  
Also your Cougar is programmed to run on regular so of course efficiency would drop with premium.
Also any one just randomly changing octane is going to have erratic results. The PCM is adaptive but it's not an "instant" change. It is a learned altering to the new setting/variable/change and it takes time. If you keep changing fuel and yes this can even mean different gas stations (i.e. brands of fuel blend) it will never run at optimum efficiency.
Trying something just once is NOT trying it. It's just being foolish really. If you really wanted to "test" a change you would reset the PCM after you filled up and drive several tanks on the same fuel to get any results worth mentioning.
My highly opinionated 2 cents on this commonly misunderstood topic. 
2000 SVT #674
13.47 @ 102 - All Motor!
It was not broke; Yet I fixed it anyway.
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excellent, I coaxed an answer from the expert.
and I hope you werent referring to me with "trying", I never used that word. I've gone through extensive periods of using high octane [for no other reason than that work was paying for it and I wanted to spend as much of their money as possible]. So I can say I've properly "tested" the change and because work was paying for it, I also had to anally log my miles. The result was about 1mpg drop and the totally unscientific, gee the car seems a tiny bit quicker.
I'm all about efficiency and only post this in an effort to more accurately understand the details.
yes... I am a cougar owner trolling on your board.
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I did a test with this on another car of mine (accord). They are made to run with reg, but I filled up with prem every other for a month or so. I seemed to get better milage with the prem, and slightly better drivability. Perhaps this is more apparent with older cars as they start to develop carbon deposits etc in the intake and combustion chamber. In any case, the slightly better milage didn't justify the higher cost of the premium.
I always use premium in the SVT. It would be different if you could manually advance/retard timing in cases where lower grade is only available, but that is not possible with the duratec. I wouldn't put anything else besides premium in it. If anything you will have a cleaner and more efficient engine even after years of driving.
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Originally posted by DemonSVT:
My highly opinionated 2 cents on this commonly misunderstood topic.
Well said.
Octane is a measure of knock resistance, nothing else.
Higher octane fuel is not any more powerful. It may permit an engine to generate more power if it is engineered for it.
Higher octane fuel burns slower (to reduce the likelyhood of knocking).
If you don't need it, there is no reason to pay extra for it.
There is more that can be said about the difference in fuel that is labeled regular and that is labeled premium, but you still really end up with DemonSVT's comments.
Jim Johnson
98 SVT
03 Escape Limited
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My friend was complaining about the price of premium the other day and I was like, ummm, don't you own a honda civic, why are you putting premium in it? He said something about hearing it was better for your car etc. I told him that his car didn't need it and wouldn't run better on it, but I don't know if he payed much attention to me 
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