Premium Fuel...

[wwest]

Some time ago the service manager at Lexus of Bellevue told me that using premium fuel grades would help to alleviate the engine hesitation symptom. My thought at the time was..."yeah, RIGHT!".

Last week I was in Memphis and the Lexus service manager there told be the same thing.

"where there's smoke there's fire..."???

So during the subsequence "windshield time" (I'm now in Tucson) I gave the fuel issue some considerable thought. The only thing premium fuel would directly affect would be the knock sensor.

I have posited in the past that these transaxles are being upshifted during closed throttle coastdowns either to extend fuel economy or reduce the potential for loss of control due to engine compression braking or possibly both. Assuming the truth of that if I were to quickly open the throttle while the transaxle remained in an inappropriately high gear the engine would certainly have a high potential to "knock". Obviously less so with Premium fuel "loaded".

But why would the knock sensor "going off" at this particular instance result in a delayed/changed shift pattern?

Software.

Having the engine develop knocking at this particular junction might be an indication to the ECU that a lower gear ratio needs to be selected "next" than would have been selected otherwise. Possibly resulting in two shifts in sequence? The first downshift due to the initial pressure on the gas pedal and now another, yet lower one due to the knocking?

While at the same time a rather low supply of fully pressurized ATF due to the low engine RPM just prior to the current incident?

The Lexus rep said the hesitation was a design charactoristic to provide for "Safety of the transmission....".

Trying to engage a new set of clutches with low ATF pressure would undoubtedly result in premature clutch wear and subsequent failure!

QUICK!

Close the transaxle pressure regulating solenoid to the next few engine revolutions (800RPM = 13 revolutions/second) can build enough ATF pressure.

[AlexD]

The guy at the dealership where I bought my RX330 last week told me that it required premium fuel. I haven't had to fill it up yet, so I haven't bothered to check the manual. Does the RX330 not require premium fuel?

[lexus411]

I noticed much better performance by using premium unleaded. No hesitation and better gas mileage.

[kevinclee]

I don't think the premium unleaded gas will help the hesitation because I have been used premium unleaded since I have mine since 2003/12.

[SKperformance]

So Kevin ,you are saying you never use premium and have a hesitation but those who do use it or started to do not have the hesitation?

[lexus411]

have the ecu flashed and switch to premium ga.. problem finished. Also do the same on the ES to eliminate hesitaion plus the sulphur smell

[Rx330driver]

the maunual says at least 91 octane of higher. Ive always filled up my RX with premium, just cause im used to it. My friend told me that PLUS gas gives the car hesitation, but the premium does the same thing. lol

[chimchim]

Some time ago the service manager at Lexus of Bellevue told me that using premium fuel grades would help to alleviate the engine hesitation symptom. My thought at the time was..."yeah, RIGHT!".

Last week I was in Memphis and the Lexus service manager there told be the same thing.

"where there's smoke there's fire..."???

So during the subsequence "windshield time" (I'm now in Tucson) I gave the fuel issue some considerable thought. The only thing premium fuel would directly affect would be the knock sensor.

I have posited in the past that these transaxles are being upshifted during closed throttle coastdowns either to extend fuel economy or reduce the potential for loss of control due to engine compression braking or possibly both. Assuming the truth of that if I were to quickly open the throttle while the transaxle remained in an inappropriately high gear the engine would certainly have a high potential to "knock". Obviously less so with Premium fuel "loaded".

But why would the knock sensor "going off" at this particular instance result in a delayed/changed shift pattern?

Software.

Having the engine develop knocking at this particular junction might be an indication to the ECU that a lower gear ratio needs to be selected "next" than would have been selected otherwise. Possibly resulting in two shifts in sequence? The first downshift due to the initial pressure on the gas pedal and now another, yet lower one due to the knocking?

While at the same time a rather low supply of fully pressurized ATF due to the low engine RPM just prior to the current incident?

The Lexus rep said the hesitation was a design charactoristic to provide for "Safety of the transmission....".

Trying to engage a new set of clutches with low ATF pressure would undoubtedly result in premature clutch wear and subsequent failure!

QUICK!

Close the transaxle pressure regulating solenoid to the next few engine revolutions (800RPM = 13 revolutions/second) can build enough ATF pressure.

←

Ok, but if it IS the software trying to protect against knocking how would 91 octane fuel help this if the knock sensor isn't going off? (no knocking = no knock sensor signal).

[scoobiedoo]

the maunual says at least 91 octane of higher. Ive always filled up my RX with premium, just cause im used to it. My friend told me that PLUS gas gives the car hesitation, but the premium does the same thing. lol

←

I was always under the impression that the RX330 required only regular 87 octane gas. Where in the manual does it state 91 or higher ? I have a 2005 FWD.

[Rx330driver]

the maunual says at least 91 octane of higher. Ive always filled up my RX with premium, just cause im used to it. My friend told me that PLUS gas gives the car hesitation, but the premium does the same thing. lol

←

I was always under the impression that the RX330 required only regular 87 octane gas. Where in the manual does it state 91 or higher ? I have a 2005 FWD.

←

well, on the last page flap, that gives Gas Station Information, it says select 87 octane...but it says for improved performance, choose 91. i guess its whatever u fell like. :D

[Booyah]

Funny we always used the lowest grade 87 fuel and always noticed a slight hesitation going through 2nd gear and just lived with it for 5000 miles---the wife drives it 90% of the time

anyway she had to fill the tank this last time and put in the mid grade gas 89 and she almost immediatly felt the car was tons smoother--I said right! Well I finally took it out for a spin and I knew what I was looking for, guess what--hesitation gone. I must have a smart wife:) So the 330 is much smoother now going through all the gears as we cruise around.....

All we run now is the Mid grade gas--so YES going up a little in octane makes a differance for sure.

[TunedRX300]

Here is a good link on engine knock, read it and decide yourself.

Gas Octane

Few quotes

"I THOUGHT GASOLINE WITH HIGHER OCTANE REDUCED ENGINE KNOCK?

It did in older engines using carburetors to regulate air/gas mix They cannot as accurately regulate the air/fuel mix going into the engine as a computerized fuel injector. Carburetors need adjustment, as a part of regular maintenance, to keep the air/fuel mix as accurate as possible. So many times, these adjustments were not made regularly causing too much fuel to be mixed with the air. When this happened the gasoline would not burn completely soaking into carbon deposits. This would cause a premature ignition of the gasoline due to the intense heat in the engine cylinder creating "engine knock." When this happened, people would change to the higher octane/slower burning gasoline to resist the premature burn, thus minimizing the knocking problem. And it worked. Good solution.

However, since the middle to late 80’s, engines are designed to use fuel injectors with computers to accurately control the air/fuel mix under all types of temperature and environment concerns. However the accuracy of the fuel injectors and computers is based on using the recommended gasoline for that engine.

Most cars are designed to burn regular unleaded fuels with an octane rating of 87. If the vehicle needs a higher octane rating of 89-93, there is documentation in the owner’s manual, as well as possibly under the fuel gauge and by the fuel fill hole. Usually you will see this rating for high performance engines only.

WHAT IF I PREFER TO USE GASOLINE WITH HIGHER OCTANE RATINGS?

You can, but there are no real benefits, other than the gasoline manufacturers making more money off of you. When you use a fuel with a higher octane rating than your vehicle requires, you can send this unburned fuel into the emissions system. It can also collect in the catalytic converter. When you over stress any system, it can malfunction or not do what it was designed to do properly. In the early 90's, an early warning symptom was a rotten egg smell from the tailpipe. Easy fix, go back to using regular 87 octane gasoline. The rude odor usually disappears after several tanks of gasoline."

Lexus recommends 87 octane, somehow many RX owners are compelled to use Toyota parts and follow Lexus recommendations but gas in a lone exception. Most ES and RX owners do not even know 87 is recommendated and assume by default 91/93 must be the recommendated fuel.

Better performance does not mean $0.20 more per gallon at the pump and therefore there must be more HP gained.

[Booyah]

I understand what that says----all I know is what I felt and experienced with my 330 when I went up to 89.

Lexus states to use 87 but also right in the manual it says 91 can be used for better performance--how much, we dont know.

[monarch]

The Service Advisor website http://theserviceadvisor.com/octane.htm is authored by a guy who admits: "I do not proclaim to be an expert in these matters".

RX & ES Lexus owners manuals do not say 87 octane is the recommended octane. They say 87 is the MINIMUM acceptable octane and for better performance use 91. Also, the Owner FAQ on Lexus's website states that the engine control system will !Removed! the ignition timing if 87 octane is used and that means weaker acceleration and greater fuel consumption. Finally, practically any engine designed to run on a MINIMUM octane of 87 (including your garden lawnmower, rototiller, etc.) will start easier and run with less stumbling and hesitation if the owner uses 89 or 91 octane.

Besides less hesitation upon abrupt acceleration, another benefit of 91 octane is that some brands like Shell put 5 times as much detergent / cleaners in it to keep the fuel injectors and intake valves extra clean which also translates into better power, fuel economy, lower emissions

and elimination of the need to use supplemetal gas additives like fuel injector cleaners.

[OKEH1]

I have used Premium for some months now,it gives me better performance, more mpg and smoother transmission changes.With the more mpg the price works out very close to using 87 so I don't worry too much about the cost difference.I would like to add my RX has had all the softwatre upgrades too and been regularly serviced by Lexus , now having nearly 33000 miles on the clock, the car is like a good wine, it seems to be getting better with age.

[TunedRX300]

There is already a 2 year long thread on octane gas in the maintenance section. Let's not go off topic and start another debate here.

Octane Thread

My question is the same as wwest, how does octane grade of gas, which burns in engine, helped tranny to shift gear smoothly?

It is equivalent of saying whatever is used (coal, nuclear, solar) to generate electricity at power plant helps transformer to step up/down the voltage of electricity delivered to your house. It is absurb unless there is a convincing reason.

[kevinclee]

So Kevin ,you are saying you never use premium and have a hesitation but those who do use it or started to do not have the hesitation?

←

Hi SKperformance,

I was saying that I have been using 91 octane premium unleaded gas since 2003/12. I can still feel the hesitation on my car.

[chimchim]

When this happened, people would change to the higher octane/slower burning gasoline to resist the premature burn, thus minimizing the knocking problem.

For the most part, I think this article is accurate EXCEPT the wording in this sentence.

The difference in burn rate is incosequential compared to the FLASH POINT of the octanes. He's getting his terms wrong.

the car is like a good wine, it seems to be getting better with age.

This is a cute analogy, but the reality is that cars don't work that way. Once the engine is broken in (within 1000 miles) it's all downhill whether we want to believe it or not. Everything is deteriorating. With the exceptions of a reflash or recall for improved parts, all cars are essentially slowly dying (like humans).

RX & ES Lexus owners manuals do not say 87 octane is the recommended octane. They say 87 is the MINIMUM acceptable octane and for better performance use 91. Also, the Owner FAQ on Lexus's website states that the engine control system will !Removed! the ignition timing if 87 octane is used and that means weaker acceleration and greater fuel consumption.

Good info. I'll have to check my manual. Can you give a link to this on the Lexus website?

If the engine is indeed retarding timing (most modern cars now have the ability to "tune down" the engine to accomodate lower octane gas... especially turbo charged vehicles for protection of the engine), then by all means a higher octane would indeed help the RX330. This would explain a "more power" feeling in 89 octane or 91. If the ECU does indeed !Removed! the timing to accomodate 87 gas, then it would have to !Removed! less on 89, and less than that to 91.

Does anyone have an Autotap, or other OBDII scanner that can confirm the ignition !Removed!? I have a scangauge but it's semipermanently mounted into my other car.

[chimchim]

A quitck google:

- 3,309 cc 3.3 liters V 6 front engine with 91.9 mm bore, 83.1 mm stroke, 10.8 compression ratio, double overhead cam, variable valve timing/camshaft and four valves per cylinder 3MZ-FE

- Premium unleaded fuel 91

If the compression ratio really is 10.8, then I'm not surprised that 91 octane is more appropriate. I'll try to look for the engine specs of the 2004.

In contrast, engines specifically designed for 87 octane for economy are of lower compression. My Civic has a 9.5 compression ratio.

So, if the above specs are right, then 91 octane is probably more appropriate for the RX330.

[stonecutter]

I'm just curious, how does the car know what octane gas you're using in order to adjust the ignition timing alluded to above ?

[TunedRX300]

A quitck google:

- 3,309 cc 3.3 liters V 6 front engine with 91.9 mm bore, 83.1 mm stroke, 10.8 compression ratio, double overhead cam, variable valve timing/camshaft and four valves per cylinder 3MZ-FE

- Premium unleaded fuel 91

If the compression ratio really is 10.8, then I'm not surprised that 91 octane is more appropriate. I'll try to look for the engine specs of the 2004.

In contrast, engines specifically designed for 87 octane for economy are of lower compression. My Civic has a 9.5 compression ratio.

So, if the above specs are right, then 91 octane is probably more appropriate for the RX330.

←

Would be interesting for you to find out the octane rating for 2004 Camry V6, it has the same 3MZFE.

This is what posted on the thread in the maintence forum on what is in ES's user manual

" SW03ES, it is very odd,

the 02 and 03 are basically the same car with the addition of adjustable pedals in the 03.

BUT:

the 02 manual calls for premium and says a lesser grade could be used in a pinch.

the 03 manual calls for regular grade and says to use premium for improved performance.

My guess is too many people complained that they "had" to buy premium so the coorporate suits reworded the section to quiet the masses and keep their behinds covered.

steviej"

[jgr7]

This is from another earlier thread in this forum, check out my posts near the end of page 2.

http://us.lexusownersclub.com/forums/index...&hl=octane&st=0

Jeff

[chimchim]

I'm just curious, how does the car know what octane gas you're using in order to adjust the ignition timing alluded to above ?

←

The car uses the knock sensor to detect knocking. Modern knock sensors are sensitive enough to detect low levels of knocking (before humans can hear/feel it) and the ECU adjusts accordingly. The ECU stores operating conditions in memory and uses fuzzy logic schemes to make adjustments. For this reason, whenever you switch octane (or do anything else to a car for that matter) it's good to reset the ECU so it has to rebuild the temporary maps.

It's sorta like calculating a GPA. Let's say you have 5 test scores in the 70% for a "C" average. Then suddenly you ace a test at 98%. Your GPA doesn't budge much. You'll have to keep acing more tests for your GPA to creep up. Now instead, erase your past test record and start getting 90% test scores and your GPA quickly is in the A range.

The ECU works kind of like that. If you've been using 87 octane, the ECU has optimized operations for that octane. A sudden switch to 91 will BEGIN to make adjustments, but it will take awhile. This of course assumes that the engine was originally designed for 91 octane.

[TunedRX300]

This is an excellent article that another member posted on the maintenance forum.

August 27, 2003

“I only use super/premium/performance/ high octane fuel in my Civic DX. I can feel the power…”

This is probably one of the biggest misconceptions in the automotive world, as we know it. Yet, I hear this all the time. For example a close friend of mine who drives a 1996 Pontiac Bonneville tells me that he only uses Chevron 92 octane fuel because “It performs so much better, and my fuel economy is way higher.” This opinion or misconception is not an isolated view to the “gear-heads” that are or think they are car savvy. And the oil companies don’t help the matter by calling their high-octane fuels “Performance” or “Premium,” or whatever they choose. Here is why.

The first thing we have to know is obviously, what is octane and why does it matter? Octane can be simply defined in one sentence: Octane is a rating of a fuels resistance to ignite (evaporative qualities). WAIT A MINUTE! Resistance? That’s right, resistance. To put it simply, the higher the octane, the harder it is to get to ignite. Higher-octane fuel resists burning. Lower-octane fuel does not. Lower-octane fuel is actually more explosive, move volatile, and creates a much bigger explosion then its higher-octane counter-part.

When you go to the pump to fill your car, you generally have three options. Regular, mid-grade, and super. You also see that there is a rating system. It is a sticker posted to the pump next to the octane rating of the fuel that you choose. It generally says something like this. Regular for example: 87 Octane minimum, measured by using the (R+M)/2 rating. What does this mean? The R in the equation stands for Research Octane Rating, known as RON. This is a test that tries to simulate variables that your car would go through on a given day. It is a test using a single cylinder, four-stroke engine that is idling at 600rpm. The fuel temperature going into the engine is not controlled. It is allowed to vary and fluctuate with the temperature of the conditions at the time. The intake air temperature is varied with barometric pressure to simulate the air being sucked into the car from the outside. The timing is set at 13° BTDC. This is done to covert everything to a SAE standard day, which is 60° F, 0% Humidity, and 29.92 inches barometric pressure.

The M in the equation stands for Motor Octane Rating, known as MON. When testing MON, the fuel is heated to 300° F and the intake air is heated to 100° F. The test engine is a single cylinder 4-cycle engine that is run at 900 rpm. Ignition timing is varied with compression ratio. Engine load is varied during test. If you are deciding what fuel to use on a high-compression, high-performance engine, this is the test you would want to use. The RON will always be higher than the MON.

So what does this all mean when you go to the pump? It means that to extract the most from the car that you are driving, you have to use the appropriate octane fuel or the car is not going to perform up to its potential. Either the fuel will burn too slowly, and in many cases not burn completely, or it will burn too fast and out of control. The latter is called Detonation. Normal combustion will take place at a pretty steady rate (for a given rpm and load), when a large amount of the charge burns extremely fast and uncontrollably, it is know as detonation. Detonation can destroy an engine in a matter of seconds. There are a few causes of detonation. Usually it is attributed to too much heat, but that is only part of the problem. Pressure and advanced ignition timing both play a role in it too. Usually when detonation takes place, the detonation occurs on the intake side of the chamber, which is the coolest side of the chamber. This happens because detonation did not occur until the pressure got excessive, which was after the spark. By the time that happened, the charge near the exhaust valve has already been burned. Most of the time, detonation will occur after normal combustion has started. Apart from destroying pistons and spark plugs, light detonation can cause all sorts of other problems, like fatiguing cranks and rods quickly and pounding bearings to death, so avoid detonation at all costs.

Another problem is Pre-ignition (for cars using octane that is too low). When the charge lights off before the spark, it's called pre-ignition. This can happen with or without detonation, but usually will cause detonation in a high performance engine. Hot spots in the combustion chamber are the usual cause of pre-ignition. This is very unpredictable and can lead to detonation, because it will act just like too much ignition timing, but it won’t be controllable.

So this is what happens in cars that use octane ratings that are too low, but what about vise-versa? Generally, the problem with using an octane rating that is too high for your car causes problems that, while not generally as severe as going too low, are still detrimental to the performance and efficiency of your engine. One of the most common problems is lost power. Yes, you read that right, if you use an octane of fuel that is too high for your car, you will lose power. This goes for all the stock or lightly modded Civics out there. Remember when we discussed that octane measures the fuels resistance to burn? Well, this is where that really comes into play in a low compression engine, such as the engines found in 90% of all streetcars. As the fuel is injected into the combustion chamber and the compression stroke begins, cylinder pressure is created. This is vital to combustion as cylinder pressure is what translates into power. When that pressure is not high enough (low-compression), the fuel only partially ignites. This means that there is leftover fuel that has to be expelled through the exhaust valves and expelled through the exhaust. This is bad for several reasons. The first is that this un-burnt fuel leaves deposits and grime all over the cylinder and valves. This robs you of power, fuel economy, and wears engine components pre-maturely. There is also a vital part of any streetcar, the emissions control devices. The catalyst for example often is destroyed by being clogged with carbon and un-burnt fuel resulting from using too high-octane. This results in costly repairs, and guess what? The loss of power and lower fuel economy. Not to mention, you had to pay $.20 more per gallon just to lower your cars potential and performance. So you guys that think that adding 100 octane race gas to your Civic Ex at the track is going to improve your times, you are running in the wrong direction unless you have some kind of forced induction such as Nitrous, Turbo, or Super Chargers.

So the next question people ask is, “Why then do high-power, ultra-fast cars use high octane fuel?” Well the answer is simple. Higher-octane fuel contains more POTENTIAL energy but requires the higher heat generated by higher compression ratio engines to properly condition the fuel to RELEASE that higher potential energy. Here is the general rule for choosing octane if you have a question of what it should be. If your compression is 9.5:1 or lower, 87 octane should be plenty. As your compression rises, so should the octane that you choose.

Remember that there are variables to everything in life and this is no exception. If you have dramatically advanced ignition timing for example, high-octane may be needed. But for the vast majority of the people on the street, for optimal performance in your streetcar, use the octane best suited for your car, and remember, high-octane does not mean more power!

Coby Burns (Writer of above topic not forum poster)

Found this at http://www.speedupgrade.com/articles/article/692608/5136.htm

[monarch]

On Toyota's website at toyota.com there is an FAQ for owners and it says this about the MINIMUM

recommended octane for each 2005 Toyota engine:

http://i5.photobucket.com/albums/y189/mastertech/.min.jpg

I hope this helps you guys understand that when Toyota recommends 87 octane, iridium spark plug changes every 120,000 miles, air filter changes every 30,000 miles, etc. that those are all just MINIMUM recommendations & service intervals, not necessarily the best recommendations and intervals to follow for maximum reliability, durability, drivability, etc.

Likewise the owners manuals of nearly all Toyotas going clear back to the 1970's say: "Use 87 octane OR HIGHER." That's Toyotas way of saying 87 octane is the MINIMUM allowable octance and not necessarily the best octane to achieve optimal engine reliability, durability, drivability, etc.