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Discussion Starter · #1 ·
So I had an interesting problem with a brand new 2018 WRX that I troubleshot and solved, so I thought I'd share my discoveries here. Bottom line; the 2.0 FA DIT is picky on fuel. About 2 weeks ago I noticed hesitation and misfiring during TWO (throttle wide open) in 2nd and 3rd gear when at full boost. Mechanically the car was running perfect. Now for a little background I have 15 years experience working on F/A-18s for the Navy, and just because an engine is mechanically sound doesn't mean there's a serious problem. I always use premium 91 octane or higher fuel, and with less than 2000 miles on the care the likely hood of a spark plug or fuel inject problem seemed awfully low, but hesitation and misfire can pretty much always be narrowed down to fuel/air matrix, or ignition system. Being under warranty I made an appointment with my Subaru dealership, but I knew there was a few things I can do on my own. With today computer controlled engines everything from injector timing, pulse width, spark timing, and valve timing can all be adjusted by the computer in fractions of a second, so problems with spark or injectors should be signaled by a warning light, but sub standard fuel that causes occational fuel/air matrix problems can be ignored by the computer.

When I had my Jeep I always fueled up at the station near my house, and never had a problem, but that engine was a low compression single cam NA engine so it wasn't picky. What I found was that, that station had a minimum of 10% Ethanol blend, even on premium fuel. Once Ethanol is introduced into the mix, all other variables of the fuel go out the window. Ethanol is a water based energy source, as opposed to a petrol, or plant based energy source with completely different chemistry. The 2.0 FA DIT engine HATES ethanol.

On my next tank of gas I filled up with Shell premium Plus fuel. My WRX ran like a completely different vehicle. Better throttle response, no hesitation, no misfire.

If you want max performance from your WRX, don't skimp on gas, and don't believe anyone that says stupid things like "all gas is the same." It's not all the same. All gasoline has to meet a MINIMUM standard, but that's far from all fuel being the same. If your having any hesitation or misfire problems, before you spend a small fortune on diagnostics, change your fuel, run a full tank through it, and see what happens.
 

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NavyOrdie, yes, the fuel very likely could have been the problem, but please don't get hung-up thinking it was because the fuel contained ethanol (By the way, I do believe fuel with ethanol can cause problems, especially when it gets old and stale). The Shell fuel also contains ethanol; it is a TopTier fuel and as such, it MUST contain ethanol. See Deposit Control | Top Tier Gas Another fact that's good to know: some states require their gas stations to label the pumps when the fuel contains any ethanol; other states do not require the pump to be labeled unless it contains more than 10% or more than 15% ethanol.
 

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By chance, this drive of yours didn't happen to be after an underway or deployment did it?

I ask because buzzw is right. Cars run fine with the ethanol mixes for a looooong time now.
But if your car was sitting and water formed in the tank, that's a possibility that would cause your issue and would be resolved by fresh gas.

And of course "bad gas" does exist as well. If.you fill up at a station that's in the bottom of it's tank awaiting a refill, you can be subject to more water and crap inside the gas you're buying.
 

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Discussion Starter · #4 ·
No, it wasn't after a deployment. My WRX is only 30 days old. I bought it July 1st. Fuel here is required to be labeled if it contains ethanol. I'm very sure it's the fuel they sell at the station around the block. This thing will not run right on it, ever.
 

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Fair enough. Either way sounds like you got it sorted.
 

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She'll uses ethanol in most of their premium fuels. The ethanol content is not related to your issue at all.

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Discussion Starter · #7 ·
It could be from water in the underground tanks, I can't discount that being the problem at all. I just know from working on aircraft that you can't run ethanol in a F414-GE-400 jet engine. They run biofuel just fine, but ethanol is no bueno. It's thinner, has a higher flash point, and no lubricity. I know jet engines a extremely different than car engines, they ignite fuel at extremely high pressures generated by the compressor fans. I just assumed that the high compression ratio of the engine and forced induction of the 2.0 DIT could cause a misfire when running a alcohol fuel blend. I'm going to research this some more and find the full answer. I'm not above getting fuel samples analyzed lol!
 

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It could be from water in the underground tanks, I can't discount that being the problem at all. I just know from working on aircraft that you can't run ethanol in a F414-GE-400 jet engine. They run biofuel just fine, but ethanol is no bueno. It's thinner, has a higher flash point, and no lubricity. I know jet engines a extremely different than car engines, they ignite fuel at extremely high pressures generated by the compressor fans. I just assumed that the high compression ratio of the engine and forced induction of the 2.0 DIT could cause a misfire when running a alcohol fuel blend. I'm going to research this some more and find the full answer. I'm not above getting fuel samples analyzed lol!
Water or contamination in the tank is the likely culprit. Ethanol of 10-15% or less has little to nothing to do with the issue.

Temperature, humidity, elevation, and other environmental factors can also cause this exact intermittent issue.

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In the US I shop for fuel based on the actual significant factors: price, how clean the lavatories are, etc.

If you suspect contamination in fuel bought legally anywhere in the US, report it. Fuel is regulated and its quality is a matter of public concern.

I find it unlikely to be the case but unlikely things happen every day -- that's why people win the lottery or why I'm still alive, for example.
 

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Yeah don't forget....jets are governed by Freedom. Nobody is doing emissions checks on military jets to make sure they aren't polluting too much.
 

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The ethanol actually increases the effective octane and helps with cooling. If it were added on top of a non-ethanol octane additive package you could actually tune the car for more power. But they don't, they reduce other octane increasing additives. E85 on the far end of the spectrum can make much more power after tuning than e10 93 octane for example. The issue with e10 is usually that it collects water and causes fuel to spoil more easily. I've gotten "bad gas" and seen it in logs, and seen it clear. It was actually when I went to a particular Shell, which I thought was better, but they had low traffic and several large "cheap" competitors next door. Now I just go to the busiest and newest looking station. They sell non-ethanol gas for a slight premium on the street here and in TN - it is advertised as such. E10 and boats is a no-no and so E0 can usually be sourced in marinas etc.. E0 is much better for yard tools and motorcycles when it sits for a while, and is less of a problem with gumming up carbs and fuel systems.
 

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mycologist said:
The ethanol actually increases the effective octane and helps with cooling. If it were added on top of a non-ethanol octane additive package you could actually tune the car for more power.
I'm happy I have 93E10 here. Before I moved back from the tundra, a lot of the stations were converting over to 91E0 as their "premium", which made my fuel supply options limited.

mycologist said:
The issue with e10 is usually that it collects water and causes fuel to spoil more easily. I've gotten "bad gas" and seen it in logs, and seen it clear. It was actually when I went to a particular Shell, which I thought was better, but they had low traffic and several large "cheap" competitors next door. Now I just go to the busiest and newest looking station.
I typically get gas at a service station at the intersection of two Interstates about 5 miles from my house. It's constantly busy.

Another thing I won't do is fill up from a station that has a refuel tanker at it. Even if I don't see the tanker at the station, if I see one nearby, I assume it refueled that station, and will not patronize.

mycologist said:
They sell non-ethanol gas for a slight premium on the street here and in TN - it is advertised as such. E10 and boats is a no-no and so E0 can usually be sourced in marinas etc.. E0 is much better for yard tools and motorcycles when it sits for a while, and is less of a problem with gumming up carbs and fuel systems.
There used to be zero-ethanol stations here that I could get 87E0 at, but that's no longer the case (they shut down); only 91E0 now at a few shops. I used to always buy E0 gas for the small carburetor engines like mowers/snowblowers, but now I alternate my 5G container between regular 87E10 gas and 91E0.
 

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I'm happy I have 93E10 here. Before I moved back from the tundra, a lot of the stations were converting over to 91E0 as their "premium", which made my fuel supply options limited.





I typically get gas at a service station at the intersection of two Interstates about 5 miles from my house. It's constantly busy.

Another thing I won't do is fill up from a station that has a refuel tanker at it. Even if I don't see the tanker at the station, if I see one nearby, I assume it refueled that station, and will not patronize.

There used to be zero-ethanol stations here that I could get 87E0 at, but that's no longer the case (they shut down); only 91E0 now at a few shops. I used to always buy E0 gas for the small carburetor engines like mowers/snowblowers, but now I alternate my 5G container between regular 87E10 gas and 91E0.
I actually got excited to find 93E0 on the way to my parent's in TN. It didn't do anything for me though. Now I just enjoy their much improved selection of non-ABC EtOH on that side of the border lol.
 

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Discussion Starter · #15 ·
I've read a lot of posts on different forums trying to solve problems with hesitation and misfire. Subis from 2004 to 2017. All these owners have spent a decent amount in doing diagnostics and changing parts. Some cars are stock, some heavily modified. The common thread is they all have the same symptoms, hesitation and or misfire at full throttle in 2nd and 3rd gear at full boost. The other common thread is that in many cases using different fuel seems to solve the problem. In other cases there was a leak somewhere in the turbo system. My working theory at this point is that ECM may have problems adjusting the fuel matrix with less stable gas. That might be why the Shell premium Plus gas fixes the problem. Shell puts detergent and stabilizer additives in their gas. From everything everybody is saying in this threat the ethanol probably had nothing to do with it at all.
 

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I can't name a fuel supplier that does not use a detergent package.
 

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Yeah you shouldn't have to be chasing after unicorn fuel. If you can find 93 vs 91 that is worth it though.

An air leak after the MAF and before the turbo would certainly be worth checking. I have had problems with that.

If it were my car I'd acquire a means to log it and look at A/F corrections, boost, IAM and any timing corrections.
 

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OP, if you found a way to cure this car's hesitation and sluggish get-up-and-go then I'm all ears. However, I doubt there's anything wrong with your car, unfortunately. Unless you flog it, this car has a slower 0-60 than my old '94 Cavalier. I'm not exaggerating. And the turbo just adds to the hesitation, tremendously.

(Flame away.)
 

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Discussion Starter · #19 ·
Christopher, my problem was completely fixed by switching gas stations. Here in Missouri we have some local stations such as Casey's, Kum-n-go, and Break Time. They all get their gasoline from the same supplier and I have problems with it. National chains like Conoco, Shell, and Phillips 66 all seem to have superior fuel (with Shell seeming to be the best) because I have no problems with them at all. My wife has a Ford Flex 3.5L Turbo V6 and while the hesitation is less noticible with her car, it doesn't like the local gas either, and today I tested by theory by filling her car up with Shell Premium, and it also made a noticeable difference.
 

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mycologist said:
I actually got excited to find 93E0 on the way to my parent's in TN.
Years ago, the local club did some testing on 93E10 vs 93E0. We found that as an overall average, we got ~2MPG better with the E0 mixture.

When it came time to refuel, I would evaluate my upcoming week. If I knew I was going to be doing a lot of light cruising around, I would go for the ethanol-free gasoline. When I was going to be up in the hills having fun, I would opt for E10.
 
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