Well there's yer problem, glad you figured it out! E10 or less from now on.
Still would like to know what code was set for this.
Now you know why it was "cheap"...lol!
On GM tricks equipped with E85, if you don't run the tank low enough before changing from E10 to E85 and you end up with an E50ish blend then the flex fuel sensor won't see enough ethanol to switch the fuel maps and it will throw codes for running lean. Need more quantity of E85 sprayed into the cylinders than E10 to produce the same energy.
What is interesting is that info for P0171, System Too Lean, does not mention E30 or worse fuel as a possible cause...
Service is one of the most profitable industries a manufacturer has. It's in their best interest to make it just hard enough to fix that the average person can't, or worse, so expensive to fix it's disposable. The only reason we even have an OBDII system that forces manufacturers to standardize the diagnosis is because of a government regulation. But I don't want to get political here. Sticking with the engineering of it, it makes sense since E85 capable systems require much larger fuel injectors and fuel pumps. They also tend to get worse fuel economy. On the flip side, E85 is way more resistant to pre-detonation, and it burns much cooler. This makes it favorable to run in high performance applications.
This surprises me, since it's only rated at 201 brake horsepower. I'm not questioning it, since I assume it's the result of your extensive dyno testing, I'm just surprised.
I could maybe see it, minimal drivetrain losses since neither transmissions use a torque converter. Both versions of the GT have a direct path to transfer power to the wheels when the clutches are engaged. No long driveshaft to the rear since it's FWD and everything is pretty light weight.
This is very true, it's not a slow car, especially for its price point, and I absolutely love that about it! I was curious how it fared performance-wise compared to other cars and found that numbers-wise, it's comparable to the most recent Civic SI. It's not priced like a Civic SI, though, and it has a DCT option to make it more accessible (that's actually the only option in Canada, there's no manual GT here).
The part I hate is that when you fuel up the message on the gas pump says: "May contain up to 10% ethanol". I take that to mean it may be 5%...6%...10%...12%...13%...15%! All depends on how much ethanol the delivery truck filler felt like putting in it...
The ACTUAL ethanol content may be the reason why sometimes it appears that you get really good gas mileage after a fill up and then the next time you fill up it seems to be worse mileage...
The OP already admitted that they bought cheap 93 octane fuel that was actually a 30% ethanol blend. The big clue was when he said the 93 was cheaper than 87. There is nothing wrong with the car or the fuel, they're just incompatible.
Octane requires higher compression to burn.
The 1.6 has a 10. 5 to 1 compression ratio and doesn't require 93 octane. Ocane is fuels resistance to burning. Only higher compression engines need the higher octane to prevent pre detonation. I run 87 all the time and no issues. Any mid grade between 87 and 93 is ok to run but your wallet is the only one who cares. Anyway run regular and keep it to the floor.
The octane rating is a measure of a fuel's resistance to knock under pressure. The "compression ratio" of an engine is a static figure that represents the difference in cylinder volume between bottom dead center and top dead center. It doesn't necessarily represent anything about the actual pressure in the cylinder. The 1.6L engine might have a compression ratio of "only" 10.5:1 (I believe it's actually 10:1), but it's also turbocharged, and it's really disingenuous to ignore that. Yes, a Forte GT with the 1.6T engine will run just fine on 87 octane fuel, but it will make even more power on 89, 91, or 93 octane fuel. Modern engines use advanced variable valve timing, fuel injection, and electronic ignitions to allow this, but what is typically happening with 87 octane fuel in a turbocharged engine is that you are taking a more powerful engine and de-tuning it so that it will still run properly without detonating. Many automakers advertise the power generated with 91 octane fuel (Ford with EcoBoost engines, for example, where they actually note the reduced hp/torque figures with lower octane fuel in the owner's manual), but Kia has apparently taken the route of advertising the 87 octane power rating, which is pretty impressive at 201hp (just over 125hp per liter). Since 87 octane or higher fuel is what they specify, they have seemingly made the choice of deliberately under-rating the performance of their 1.6T engine for whatever reason. In any case, it makes the Kia Forte GT an exceptionally good value for its price point, and a very fun car indeed.
