Hello,
I have a tricky question. On my Ford Escape 2014 2.0L AWD turbo, I always fill the tank with octane 91 gasoline and I am always getting a 535 km distance to empty (could be 525, I’ll document next time).
With gas prices going through the roof in the beginning of summer, I decided to fill the tank with octane 87 just to try and the distance to empty went down to 469 km (I still had a little bit of octane 91 gas in the tank). This new value puzzled me, considering that I never thought that my car “knew” the octane level in my tank. In fact, I became so curious that I decided to fill with octane 94 once the octane 87 tank was empty and the distance to empty jumped to 610 km!
I decided to reset the trip counter to 0 and see how accurate this 610 km number would be. Since I live in the country and riding all the time on highways, I drove 300 km and strangely enough, the distance to empty seemed pretty accurate.
How is this possible?
The engine control system is adapting to the higher octane gas and running more efficiently.
Wow. This is great! Funny enough, I did the same test on my old Ford Focus 2003 and i noticed a small difference from 87 to 91 (I usually fill with 91). I also tried octane 94 but I didn’t see a difference. Obviously the old car cannot detect different levels of octane.
It's more a matter of your older Ford not being designed to do things like advancing the ignition timing sufficiently to make a difference. Octane detection is typically based on knock sensor data.
This is what I was suspecting (advanced timing). A friend of mine explained it to me and I told him that from this value it was certainly possible to determine the octane value. on the Focus 2003, I determined that octane 87 was degrading a bit performance because I drive through a mountain top every day. I was however a bit surprised to have noticed nothing more with octane 94.
It shouldn't come as a surprise. The reason your engine is fitted with a turbocharger is so that it can extract more power from the gasoline. Turbos are how manufactures are able to squeeze out such high economy numbers these days.
The higher octane fuel allows the engine to add more turbo boost and advance the ignition timing.
I never thought that my car “knew” the octane level in my tank.
It doesn't. The computer is simply always pushing the engine as hard as it will go until it starts to detect incomplete combustion using highly sensitive knock and crankshaft position sensors. The higher octane fuel simply behaves better in those conditions.
Obviously the old car cannot detect different levels of octane.
A 2003 Ford Focus is likely new enough to detect octane ranges. The technology in computer controlled cars started coming out in the late 90s with Flex-Fuel vehicle introduction (my 1999 Ranger is a flex fuel vehicle and it detects the Octane change). My 1994 BMW also detected octane changes. Owner's manual said to use premium gas for best performance.
You would need to go back to the late 70s and up through probably the early 90s to genuinely find a car that can't detect octane changes. For example, my '79 Catalina is carbureted, it doesn't "know" the octane, it just mechanically meters whatever liquid is in it to go in the engine. Putting high octane gas in when the engine is designed for regular is just wasting money (my compression ratio is 8.5:1, a modern car like that Focus is more like 9:0-9.5:1 or higher)
As I wrote in a previous comment, I saw improvement from 87 to 91 but none from 91 to 94 with the Ford Focus, although I haven’t checked the mileage yet (which is harder to evaluate unless using a good old fashion gas canister and measure).
Basically it depends on whether there's provision for knock sensing. My old 1985 AMC Eagle's six cylinder engine had a carb and a distributor but also had a knock sensor, O2 sensor, and ECU. It could vary the ignition timing for individual cylinders based on what the knock sensor was reporting. However it would not advance timing enough to take noticeable advantage of high octane fuel.
My daily driver 1997 Saab uses the spark plugs as knock sensors for each cylinder via electronics in the coil pack and definitely takes advantage of high octane fuel. I drive pretty conservatively though and find that mid-grade works fine. You can only feel it cutting back if you really put a heavy right foot in it. If I put in regular the car will run on it but you can really feel the engine control system holding back the turbocharger and ignition timing. (That system first debuted for 1992.)
It makes a lot of sense because when I’m crossing the mountain ridge, I have to downshift the Focus because it has a manual transmission with a Zetec engine. When I filled with octane 87, the car was not able to maintain speed in fourth speed compared to octane 91. I still have plenty of octane 94 to test furthermore. Thanks! And by the way, I was a AMC fan too. My dad had bought a Hornet 70, a 77 Pacer and a 80 Concord DL 3 litres. I drove the three of them and they were great!
@chucktobias that's interesting about your '85 AMC Eagle, a carb with knock sensors, O2 sensors and ECU. AMC was always the oddball brand that had interesting technology and ideas. I started our '61 Rambler the other day and did not need to prime the carb before starting it. Starts like a modern car, at the turn of the key. Too bad the brand got bought out by Chrysler.
I think the 3.0 Vulcan was a little more similar to a modern design, it never had a carbureted model, only EFI with an ECU and fuel rail. It came out in '86. The pushrod and single cam design were old school.
I'm curious how a spark plug doubles as a knock sensor in your Saab. That's very interesting.
AMC always seemed to have a strange combination of advanced and obsolete technologies. The Eagle was ahead of its time in a lot of ways yet was built on the bones of the 1970 Hornet, which in turn was heavily based on the 1963 Rambler Classic's unit structure.
The Saab "Trionic" engine management system uses the spark plugs to measure ionization in the cylinders which corresponds to pre-ignition, adjusting timing and turbo boost as required to adapt to whatever gasoline is being used. (It was quite an advanced system for 30 years ago.) The "magic" is electronics in the coil assembly which is referred to as the Direct Ignition Cassette (DIC). The downside is you cannot replace individual coils, the DIC must be replaced as a unit if anything goes wrong with it. Also the factory-specified NGK plugs need to be used for the system to work properly, changed relatively frequently (every 24K miles). Fortunately the plugs are inexpensive and, at least on 4-cylinder models, very easy to change.
why octane 94 did not improved on octane 91.
Like it was explained before. Your vehicle is not able to take advantage of it. You have run into your engine's designed limitations.
Even 91 octane shouldn't have made a significant difference since Ford recommends using 87. You may have some deposits in your cylinders and a fuel system cleaning could restore some engine power so 87 will feel more like 91.
Very unlikely carbon deposits because engine only has 68,000 miles on the counter. Thanks anyway. I think indeed that using octane above 91 is useless. This car has always been filled with premium 91 since new.
In fact, it's very likely since the 2.0L is direct injected.
But I guess you don't need us since you already know everything. Good luck.
Very unlikely carbon deposits because engine only has 68,000 miles on the counter
It quite is likely - That's when it really begins to build up on most GDi engines, depends on your driving style.
I’d be a bit surprised because that car don’t do city driving, I live by the country side. Also, I always fill with premium gas that contains detergent (and no ethanol). It runs as good as it was running when I bought it 20 years ago. I also have a very good mechanic but It is always a possibility.
I just did an empirical test this summer given that I am driving that particular stretch of road twice a day, nothing strictly scientific but it surprised me that I was getting a bit more kick with octane 91 over octane 94. The car being manual, it makes it easier to test in steep hills. I’m not going to use an injector cleaner yet because it is a beautiful car and it runs just fine. BTW, Is there a way to upload photos in a post on this site? Didn’t find it..
Instructions for photos are in the "Read this first" post that is prominently displayed near the top of the page:
https://carkiller.com/scottykilmer/qa/read-this-first/
Yes, I was just reading! I’ll post something.
Ah. That’s what I had figured. No direct uploads.
Carbon build up (on the intake valves) has nothing to do with injectors.
Here's an example or carboned up valves vs normal valves with no build up.
I do not know if your car has buildup or if it's super prone to it, but most GDi engines have that issue at some point.
I guess I would need a snake camera to check that? Or open the valve cover? I check the plugs and they are A1. I wouldn’t certainly not venture in that if there a no problems with it. Will try to post a few pictures tonight.
Your valves/runners are NOT under the valve cover.
With a turbocharger, knowing how much it can compress fuel before it detonates (aka. the fuel octane) is a must.
Otherwise the detonation makes the pistons fall apart, but it really wasn't implemented all that well on the Ford 2.0T.
The car uses the knock sensor (pretty much a microphone strapped to the engine block) to look for detonation.
The car will alter with the ignition parameters until it finds a value where it gets the most power but no knock.
Using the parameters it figures out and built in data tables, the car can guess the fuel's octane level.
There's a guy online who reverse engineered the ECU firmware on a '90-'99 Toyota MR2 turbo,
So here's a lot of information on how octane level detection was implemented on a 37 year old engine,
https://www.mr2oc.com/threads/facts-regarding-the-stock-ecus-high-and-low-octane-modes.215475/
Obviously, modern engines are way more complex, and most don't limit themselves to two octane levels and 3 measurements throughout the power band - I'd assume that it's all on a linear scale with measurements throughout the entire power band.
Well, this is strange.
Yesterday, I filled my Focus 2003 with octane 91 (from octane 94 last week). Driving through my usual mountain ridge today, I felt that the Focus had more power with Octane 91 than 94. I was already not impressed with octane 94 last week.
There is a particular hill on my route that I use for testing. Simple enough: I downshift in fourth speed and set the cruise control to 100 km/h. With octane 87, it could not hold its speed by 7-8 kilometres. With the 91, it would lose only 1-2 kilometres and with octane 94, I noticed 4-5 kilometres.
If I interpret this correctly, the advanced timing could not cope with octane 94? How can this be explained?
did you measure the wind on that particular day? Ambient temperature and barometric pressure? humidity level? Battery voltage?
Did you weigh the vehicle? Measure the octane of the particular mixture in your tank?
I think your test is meaningless.
I’ll forget your last comment.
I’ve been driving my very same Focus 2003 since 19 years. Bought it new. I know it inside out. I’ve been testing for three months with different levels of octane under all kinds of circumstances (Focus and Escape). I considered weather, humidity, rain, level of gasoline in the tank, etc. It is always possible that I purchased octane 94 gas that was not as advertised (although I only buy from the best outlets). Battery is new BTW from May. I am also checking it from time to time with a trickle charger to see if it’s fully charged or not. For the mixture, especially for the 94 octane, I made very sure that my Focus tank was empty: I even brought with me a gallon of gas in a can in case I would run out of gas because the tank was at a critical level. This is not a 100% scientific rigorous test but it has some intelligence behind it. And why would I weight my vehicle? Because I drank a soda can before leaving?
I was expecting octane 94 to give a bit more kick on the Focus, but no. Actually, I noticed that on the same stretches of the road that I’ve been driving daily since April, octane 94 did not seem to improve on octane 91 and even being incapable of sustaining the speed of the car with octane 91, but not by much.
My conclusion is that filling the Focus with octane 94 did not provided a few extra horsepowers. However, the difference between octane 87 and 91 was very clear throughout summer. Also, I have not checked on the Focus if the mileage increased from higher octane 94 but on the Escape, it definitely did.
Because of that testing, I’ll continue to fill up with octane 91 on both cars because the closest outlet with 94 is at one hour drive from my house. However, I’m curious as to why octane 94 did not improved on octane 91.
Enough already.
Agreed. Topic closed.