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Old 11-19-2020, 06:12 PM   #1
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Engine Knocking from Ethanol in Gas Diagnosis

So took my 2018 Forester into the local Ford dealer (E450 chassis/V10 engine) with engine knocking issues. Dealer said they could see computer trying to compensate for knocking and ran a gas analysis from my tank. 12% ethanol content found that they say is causing the issue. (Yes I know 10% is generally the max legally so not sure how that happened!)

The dealer says use Ethanol Free gas but that is extremely hard to find these days. I asked about using Seafoam or Sta-bil with ethanol gas and he really discouraged me. I asked about using Premium gas as my norm (many times it does not have ethanol) and he discouraged that too since my engine is made to run using 87 octane regular.

So I'm kind of stuck in how to approach this moving forward...particularly to minimize/eliminate my knocking issues. I'm sure some of the gas burners have figured out the best "cocktail" for these engines and performance and look forward to your input.
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Old 11-19-2020, 06:29 PM   #2
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If I had an issue with an engine knocking sometimes, the first thing I'd do it top off with premium. And use that tank, before filling fresh with premium. If the problem goes away, it was bad gas or just not high enough octane.
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Old 11-19-2020, 06:34 PM   #3
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If I had an issue with an engine knocking sometimes, the first thing I'd do it top off with premium. And use that tank, before filling fresh with premium. If the problem goes away, it was bad gas or just not high enough octane.
^^^^ What he said. That's what I do and it usually fixed the 'knock'.
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Old 11-19-2020, 06:39 PM   #4
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I'd buy gas at a different location and I would take your mechanics suggestion.

Around here all I have ever seen is premium that is ethanol free but while traveling I often see 87 ethanol free. -Your issue is the ethanol and if all you have is premium that is ethanol free I would use it because your motor can compensate for the octane but doesn't like ethanol above 10%.

Try this site...it isn't perfect but I've found it pretty reliable.
https://www.pure-gas.org/
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Old 11-19-2020, 06:43 PM   #5
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Strange. Ethanol has been used for decades to prevent knock/detonation.

Supercharged aircraft engines had "Alcohol Injection" to keep from blowing holes in the pistons at high boost pressures.

Like I said---------strange.

If it were my rig I'd find another place to fill up.
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Old 11-19-2020, 07:06 PM   #6
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If I had an issue with an engine knocking sometimes, the first thing I'd do it top off with premium. And use that tank, before filling fresh with premium. If the problem goes away, it was bad gas or just not high enough octane.
It's not bad gas or too low of octane (spec's call for 87...I've been putting in mid-grade 89 octane.) So are you saying you always use Premium in your gas burner or you think a tank of Premium (or two) might solve the knocking issue?
(Using Premium that doesn't include 10% ethanol could be the answer but an expensive one.)
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Old 11-19-2020, 07:23 PM   #7
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I'd buy gas at a different location and I would take your mechanics suggestion.

Around here all I have ever seen is premium that is ethanol free but while traveling I often see 87 ethanol free. -Your issue is the ethanol and if all you have is premium that is ethanol free I would use it because your motor can compensate for the octane but doesn't like ethanol above 10%.

Try this site...it isn't perfect but I've found it pretty reliable.
https://www.pure-gas.org/
I'd buy gas at a different location and look for a different mechanic. If the computer is pulling timing to compensate for preignition (which is exactly what it is supposed to do), but is still getting knock, then the simplest/easiest next troubleshooting step is different/better gas.

"Discouraging" using premium is a strange position to take. It could (in theory) reduce gas mileage very slightly, but it can't do harm - other than to your wallet.

On modern engines with knock detection, the computer will advance ignition timing until it detects knocking, and then back it off until the knock stops. It does this hundreds of times per second. The idea is to always run right on the verge of knocking.

The earlier the timing, the earlier the spark plug fires, and the more complete the fuel burn for each engine cycle. More power, better efficiency. If the spark is *too* early, then peak cylinder pressure occurs before the piston finishes the compression stroke. This causes the piston to be fighting against the "flame front" of the burning fuel, which best case reduces power - and worst case burns holes in the tops of your pistons.

The main difference between "regular" and "premium" gas (apart from marketing BS and 20+ cents per gallon) is that premium has additives to make it less volatile so that it is less inclined to self-combust under high compression conditions like you see in performance cars and forced-induction engines. For normally aspirated engines, and under normal conditions, there would be no benefit - in those cases, the computer is not programmed to advance the ignition far enough to take advantage of the increased octane.
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Old 11-19-2020, 07:38 PM   #8
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Strange. Ethanol has been used for decades to prevent knock/detonation.

Supercharged aircraft engines had "Alcohol Injection" to keep from blowing holes in the pistons at high boost pressures.

Like I said---------strange.

If it were my rig I'd find another place to fill up.
As I understand it from my Ford dealer, no problem with ethanol if you are pretty consistently turning the tank over (using gas/refilling) but my RV can sit for 3-6 weeks at a time and that's when I'm getting issues. (And I normally try to store my RV with a full tank to minimize condensation/water.)

I do agree that ethanol has been used a long time now...a shame the manufacturers (like Ford) that are selling these chassis' to the RV industry aren't tweaking the engine computer a bit to handle this better. Not everyone is a full-timer driving weekly. Wishful thinking.
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Old 11-19-2020, 07:47 PM   #9
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As I understand it from my Ford dealer, no problem with ethanol if you are pretty consistently turning the tank over (using gas/refilling) but my RV can sit for 3-6 weeks at a time and that's when I'm getting issues. (And I normally try to store my RV with a full tank to minimize condensation/water.)

I do agree that ethanol has been used a long time now...a shame the manufacturers (like Ford) that are selling these chassis' to the RV industry aren't tweaking the engine computer a bit to handle this better. Not everyone is a full-timer driving weekly. Wishful thinking.
If you have water in your tank you'd be having other problems than pinging.

Another cause of pinging is carbon buildup in the cylinders. This can occur with gasoline that doesn't contain enough additives to prevent this (translated to cheap gas). or even burning some pil. Doesn't take a lot, just enough to put carbon in various corners of the combustion chamber.

When you fill up next time try to do it at a "Top Tier" station if you aren't already. Look at the "Top Tier website to see which stations around you are part of that program. Refiners and Car manufacturers have joined hands so to speak to see to it that gasolines under this "Label" have the max amount of additives needed to keep insides of engines clean.

Where I live it's SHell, 76, and several others, Check it out and see if a change might be in order. Face it, there's a reason that "Cheap Gss" is Cheap.
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Old 11-19-2020, 07:48 PM   #10
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It takes some very sophisticated equipment to determine how much ethanol is in a sample of gas. I doubt any mechanic has it. I think he is pulling your leg because he doesn’t know what the problem is and is just kicking the can down the road.
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Old 11-19-2020, 07:49 PM   #11
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Ethanol

The issue with ethanol is the shelf life of the fuel is very short, compared to ethanol free. Try a different gas station. I add fuel stabilizer to The fuel I have that is not going to be used right away.
Around here itís hard to find 87 octane without ethanol.

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Old 11-19-2020, 07:59 PM   #12
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Originally Posted by ArkRVHog View Post
It's not bad gas or too low of octane (spec's call for 87...I've been putting in mid-grade 89 octane.) So are you saying you always use Premium in your gas burner or you think a tank of Premium (or two) might solve the knocking issue?
(Using Premium that doesn't include 10% ethanol could be the answer but an expensive one.)
As was explained by qwkynuf, your engine wants to advance the timing as much as possible. If it detects knock, it retards the timing until it goes away. But it has a range. If it's knocking, either the knock detection or timing adjustment aren't working, or it doesn't have enough range to compensate for extra low octane gas.

I assume your mechanic would have spotted a problem if there is one, but maybe not. A second opinion may be worth the extra hassle and cost. But first, you could experiment with potentially weak or contaminated fuel. Best would be to drain the tank and refill with premium. But it would be far easier to dilute what you have with premium and use it up before trying a fresh tank of pure sweet premium...

If it still knocks by the time you are halfway into that fresh tank, then you definitely have some sort of issue that a mechanic will have to dig into.

As was mentioned earlier, and to answer your question, using a higher octane than required is generally a waste of money, but no harm. You should be able to use 87 if that's what the manual calls for, unless something isn't working right, or you got a tank full of contaminated gas somehow. The tank of clean premium will show if it's a fuel or a vehicle problem.

I hope some fresh gas is all you need!
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Old 11-19-2020, 08:05 PM   #13
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It takes some very sophisticated equipment to determine how much ethanol is in a sample of gas. I doubt any mechanic has it. I think he is pulling your leg because he doesnít know what the problem is and is just kicking the can down the road.
Sadly there way too many of them. If the computer can't give them the answer they're lost. Good mechanics rely on there skills and knowledge along with the computer.
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Old 11-19-2020, 08:47 PM   #14
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It takes some very sophisticated equipment to determine how much ethanol is in a sample of gas. I doubt any mechanic has it. I think he is pulling your leg because he doesnít know what the problem is and is just kicking the can down the road.
I had this same thought, but a quick Google search suggests that it is fairly easy. We know that water and gasoline don't mix, but that alcohol is hygroscopic (attracts water).

In the test that I saw, they use a graduated cylinder (fancy measuring cup), and put 10ml of gas in. Then they add 2ml of water. Cover the mixture and shake hard to mix.

Now let it sit for 15 minutes. the gas and water will separate. If it separates right at the 2ml line (water on bottom, gas on top) then there is no alcohol in the gas.

If the separation line is above 2 ml, then that means that alcohol that was in the gas bound itself to the water, increasing the perceived amount of water.

Then it's simple math - if the separation line is at 3ml, that would mean that there was 1ml of alcohol in 10ml of gas, or 10% (3ml separation line minus the 2ml of water added leaves 1ml of alcohol)

Not *super* accurate, but pretty slick nonetheless.
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Old 11-19-2020, 10:03 PM   #15
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I agree with using top tier gas. It's all I ever use and I've never had any engine knocking issues. And I'm using the recommended grade for each vehicle. We can't get gas with ethanol in it where I live, but even when I've driven in areas where it's available, I've never had an issue with knocking.
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Old 11-19-2020, 11:12 PM   #16
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I smell BS.
I spent over 25 years as an auto mechanic, specializing in driveability and computer systems. Automotive gasoline will meet certain octane ratings (in theory; more on that in a bit). Ethanol is not going to drop the pump octane rating excessively below the number.
Modern auto computer systems compensate for knock using a combination of a knock sensor and cross-checks with other engine parameters.
If you are getting knock (which is pre-ignition caused by fuel detonating in the cylinders before the spark occurs), you have one of only a few causes. One, the octane rating of the fuel has dropped significantly below the pump rating (i.e., 80 instead of 87, for example); this could happen if something happened to the fuel load such as contamination, two, the engine control system is not sensing the knock so is unable to compensate for it, three, the knock is so pervasive the system doesn't have enough range to compensate for it. The last is usually a problem with engine mechanical or carbon buildup.
I have never seen an auto mechanic that had the tools and equipment to test fuel octane. It's possible that you got a load of bad gas but a refill with a different brand should prove that out. Alcohol content can be roughly checked but being able to tell the difference between 10 and 12%? Without lab equipment? Maybe... LOL
More likely that you have a sensor issue in the engine. Get a second opinion from a really good driveability shop OTHER than a dealer.
One last thing to look at... if it only happens when moving and under load, especially at higher road speeds, inspect the tires and compare the sizes to the recommended specs. If your tires are a bit too large, you can get knock that is beyond the ability of the computer to compensate.
Good luck!
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Old 11-20-2020, 12:48 PM   #17
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I smell BS.
Ethanol is not going to drop the pump octane rating excessively below the number.
Ethanol (as well as Methanol) is added to gasoline to enhance it's Octane numbers. Ethanol is preferred as it has 75% of the heat content as gasoline where Methanol is about 10% less.

There is so much BS floating around on the Internet about Ethanol it's being blamed for just about everything that goes wrong with engines.

Funny story
I have a friend who is so anti-ethanol he has a sticker in his rear window promoting an "ethanol free" website. He's a fellow "shooter' and when we don't see him at the range someone will ask "Where's Ted?"

Answer: "Ted's truck is down again with fuel problems".

He has to drive 25 miles to a station that sells Ethanol Free fuel that charges ONE DOLLAR more per gallon.

We all think he enjoys the pain
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Old 11-20-2020, 01:05 PM   #18
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[QUOTE=ArkRVHog;2453460]So took my 2018 Forester into the local Ford dealer (E450 chassis/V10 engine) with engine knocking issues. Dealer said they could see computer trying to compensate for knocking and ran a gas analysis from my tank. 12% ethanol content found that they say is causing the issue. (Yes I know 10% is generally the max legally so not sure how that happened!)

The dealer says use Ethanol Free gas but that is extremely hard to find these days. I asked about using Seafoam or Sta-bil with ethanol gas and he really discouraged me. I asked about using Premium gas as my norm (many times it does not have ethanol) and he discouraged that too since my engine is made to run using 87 octane regular.

So I'm kind of stuck in how to approach this moving forward...particularly to minimize/eliminate my knocking issues. I'm sure some of the gas burners have figured out the best "cocktail" for these engines and performance and look forward to your input.[/QUOTE

Typical quote from a car/truck salesman. Run some premium in it. Also a bottle of Sta-Bil 360 wont hurt.
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Old 11-20-2020, 01:08 PM   #19
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The root cause is that the engine knocks when it shouldn't, and the fix to the root cause is that the manufacturer needs to build an engine that runs on the specified fuel without knocking. Period.
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Old 11-20-2020, 01:17 PM   #20
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The root cause is that the engine knocks when it shouldn't, and the fix to the root cause is that the manufacturer needs to build an engine that runs on the specified fuel without knocking. Period.
Or do like Falconer said, find the part the manufacturer included in the system that prevents knock and repair/replace it.

Everyone wants to blame the manufacturer when something goes wrong but perhaps it's just the mechanic who couldn't find the defective part or other cause.

I remember when the first "knock sensors" were introduced. People would complain about poor fuel mileage/low power and in a lot of cases it had nothing to do with the engine or faulty knock sensor. There were enough loose parts that nobody tightened/repaired that the knock sensor thought the engine was knocking and it told the computer to retard the spark.
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