'08 Escape V6: Better performance with higer octane gas?

[Lagerpe]

Hi,
I'm new to these forums, so this is my first question.
I have a new '08 Escape V6 and I wonder if the Duratec 30 engine in the car has a knock sensor and, thus, if it would benefit from filling it up with 93 octane gas rather than just regular. If so, will I notice any performance gain in real life?
Thanks in advance for any comments on this!
Cheers,
Lagerpe

[GaryG]

I would run the lowest octane the owners manual recommends. Using a higher octane may decrease your MPG by changing the long term fuel maps stored in the KAM (keep alive memory). Fuel maps are stored in your PCM so at different engine loads and RPM's they don't have to be constantly adjusting the air/fuel ratio. A change in the octane or adding ethanol to the gas will cause the fuel maps to be relearned in KAM. During this time (about 3 tanks of gas), mileage will suffer. In the end, a higher octane may not hurt your mileage, but it will most likely not improve MPG.

Some manufactures design engines for high octane fuels but state you can run lower octane fuels also. The Toyota Highlander Hybrid V6 manual for example states this. People have reported better MPG with the higher octane in that vehicle.

I added 93 octane to my Ford Escape Hybrid by mistake and saw a quick drop in mileage right away. It wasn't as bad as ethanol, but I noticed the drop in MPG on my Scangauge throughout the tank. If you want to improve your mileage, you can monitor your driving habits with a scangauge, see scangauge.com about this device if you like. If you really want to learn how to improve your mileage, visit CleanMPG.com and post to that group. CNN has been doing stories about that site and Hypermiling. There is an article on that site I wrote called "Hypermiling The Ford Escape Hybrid" but the site is for non hybrids also.

[Lagerpe]

GaryG,
Many thanks for these comments. They were very interesting to read. I take it that this adaptive function is indeed made possible by the presence of a knock sensor, right?
I am almost ashamed to admit it, but I was not referring to MPG performance, but rather to bhp performance (horse power).
So, the question remains: will 93 octane gas give higher bhp and will the difference be noticeable?
Lagerpe

[GaryG]

Originally Posted by Lagerpe

GaryG,
Many thanks for these comments. They were very interesting to read. I take it that this adaptive function is indeed made possible by the presence of a knock sensor, right?
I am almost ashamed to admit it, but I was not referring to MPG performance, but rather to bhp performance (horse power).
So, the question remains: will 93 octane gas give higher bhp and will the difference be noticeable?
Lagerpe

In the '05 workshop manual, only the I-4 2.3L has a knock sensor. There is no knock sensor listed for the V6 3.0L engine. The adaptive system comes from feedback from the heated oxygen sensors located before and after the CAT converter. The PCM adjust the fuel mixture from the O2 sensors feedback.

In my younger days when I built race engines, high compression required high octane to prevent premature ignition (knock). The higher octane had a slower burn rate and allowed the fuel to be completely compressed so the spark plug would fire the explosion in the cylinder at the right time. This made for more power because the explosion wasn't premature before the piston reached the top of the compression stroke. The lower octane produces more energy and a faster burn rate (explosion) in the cylinders if premature ignition is reduced because of less compression and better timing control.

If higher octane would increase HP, it would also increase fuel efficiency in lower compression engines. In lower compression engines like your V6, high octane is a waste of money. I presently hold the record of 61.8mpg in the Ford Escape Hybrid at the '07 MPG Challenge. If 93 octane would have increased my efficiency with more HP, I would have ran with it.

If you haven't heard, the '09 3.0 V6 Ford Escape comes with 40 more HP and gets better mileage than the '08 V6 Escape. The new Escape also comes with a new 6 speed transmission. It runs on 87 octane also.

[Abusch]

The Bottom Line Most cars don't need premium, but a few do -- and not necessarily the ones you'd expect. And premium's not likely to "clean" your engine, either.

While many people claim that their car runs better on premium, this costly fuel is really only needed in a few circumstances. However, when it is needed, it must be used to spare your engine from costly damage. On the other hand, if you burn premium when your car doesn’t need it, the damage won’t be to your engine but only to your pocketbook.

It’s All In The Numbers

The AKI (anti-knock index -- also known as "octane rating") of the fuel is an average of two different methods of computing the fuel's ability to resist engine knock. Regular unleaded gas in the U.S. has an anti-knock index of 87, while mid-grade is usually 89, and premium typically is 91 - 93. The higher the number, the more anti-knock protection the fuel offers.

Engine knock occurs when the fuel in the cylinder ignites by itself before the spark plug ignites it. The technical name for this condition is "pre-ignition." It sounds like marbles rattling around in a can, and it generally gets worse the harder you press on the accelerator pedal.

Knocking can indeed damage an engine because what is in effect happening is the "explosion" of the fuel/air mixture is trying to push the piston downward in the cylinder before it's gotten to the top of its stroke and is free to move downward. The engine is actually working against itself to a degree, and there is a lot of mechanical stress placed on certain engine parts, such as the pistons. In extreme cases, knocking can burn holes in the pistons and create other forms of engine damage.

Oil companies sell higher AKI fuels (also known as premium) to address this problem. A fuel with a higher AKI actually burns more SLOWLY than fuel with a lower AKI. This is because the fuel is less volatile and requires more heat input before it begins to ignite.

Who Needs Premium?

1. If your vehicle makes the above-described knocking sound when you accelerate, try the next higher grade when you refuel, and then see if the knocking goes away. If it does, stick with that grade. If not, bump it up another grade the next time you get gas. Generally speaking, high mileage vehicles with a lot of carbon deposits in the engine are likely candidates for needing premium or mid-grade gas, since these deposits reduce the volume of the engine's combustion chamber and make knocking more likely. In addition, the carbon deposits themselves get hot and may act to ignite the fuel if lower AKI fuel is used. High mileage engines do not always have carbon deposits; those that have been driven mainly in town and done a lot of idling are most likely to be “carboned up.”

2. If your owner's manual calls for higher AKI fuel, use what the Good Book says. Usually this will be specified by manufacturers of high compression, high performance engines. If lower AKI fuel were used in these engines, performance would suffer because the engine's computer system would have to retard the ignition timing (reducing horsepower and fuel economy) to keep the engine from knocking.

If, in such an engine, the computer could not retard timing enough to keep it from knocking, the engine itself could be damaged. This would not be likely to happen on one tank of fuel, however. So if you lend your BMW to your son or daughter who has a hot date, don’t run for the siphon hose if he or she returns it with a full tank of regular unleaded. Just drive more easily than normal so the engine's maximum performance isn't needed, and there should be no problem.

[Lagerpe]

Thanks for this information! However, I still have not received final confirmation about whether or not a 2008 V6 Escape engine (Duratec 30) has a knock sensor...

Would anyone here, with access to the 2008 service manual, be able to confirm the presence or absence of such a sensor?

Many thanks in advance!

Lagerpe

[mkaresh]

I thought all engines these days had knock sensors, but maybe not.

Either way, premium won't have any significant benefits in this engine. If it doesn't say "premium required" or "premium recommended" on the filler cap / fuel gauge, premium is a waste of money.

[Lagerpe]

Anyone who knows for sure whether or not this 2008 engine has a knock sensor?

[Abusch]

I just spent an hour GOOGLING this question and it appears that this engine does have a knock Sensor. In fact, several sites say that ALL modern electronic controlled engines have Knock Sensors, as it not only controls engine knock, but is a big part of the emission control system.

[GaryG]

Originally Posted by Abusch

I just spent an hour GOOGLING this question and it appears that this engine does have a knock Sensor. In fact, several sites say that ALL modern electronic controlled engines have Knock Sensors, as it not only controls engine knock, but is a big part of the emission control system.

I think you answered the question, there is no Knock Sensor. However, that doesn't mean Knock is not inferred by other sensors by the PCM. This is like coolant temperature is inferred by the PCM by the head temperature sensor in my FEH. Ford wants to eliminate as much wiring and sensors due to cost. The PCM (computer) can be programmed to determine knock with other sensors and adjust timing accordingly in the 3.0 V6.

Does the FEH have a coolant temperature sensor? No, it's inferred by the head temperature sensor by the PCM.

Just like the O2 sensors don't give the CAT temp, but the PCM can determine that the Light-Off of ~550 degrees is okay for closed-loop. It's all inferred by the PCM based on readings of the O2 sensors.