dynomite05

93 all day here!

mac911

Yes, I know the numbers are a different formula, but more than our 91 is recommended in Europe.

jsap

Believe in "mythology?" Once again, you prove that you've never finished high school. Mythology is the study of myths. You believe in myths.

As for your reasoning that Mercedes engines cannot handle lower octane, let's go step by step:

1. These cars are sold all over the world without modification in locations where 91-octane equivalent gas isn't available.

2. Older mercedes manuals printed before the use of ethanol do not have any of the 3000 RPM, 2/3 throttle, and other warnings.

5. When the knock sensor data causes ignition timing to fully retard, OBDII will offer a knock sensor related code. I've run 87 octane gas several times, and I never gotten a code.

4. At higher RPM's, knocking is reduced due to better air/fuel mixing in the chamber. So, why would Mercedes say on their ethanol-era manuals to maintain less than 3000 RPM (and on their later Liquid publication, revise this even lower to 2000 RPM)? Ethanol.

5. At higher RPM's, manifold pressure increases, and ethanol is increasingly at risk of pre-ignition, especially on engines that approach 100 KPa or greater.

6. Ethanol degrades. Your 91 octane gas is a mix of 110 octane ethanol and 89 octane gasoline. As ethanol degrades over the weeks, the gas in your tank is lower in octane. When you put 87 octane in your tank and you wait a few months (which is plausible if you use your car only occasionally), you've have 85 octane gas. On a car that calls for 91 octane, 85 octane is very low.

What to do about it?

To reduce the risk of pre-ignition with E10 gas, use a colder spark plug and reduce the electrode gap (see NGK Canada TSB, which I've used as a basis for my own ongoing experiment). I'm using BCP6ES with 0.028" gap. Factory spec is BCP5ES with 0.032" gap.

Btw, if you like myths, here's one just for you:

http://www.cartalk.com/content/featu...ths.html#myth4

Also, here's someone who's been around:

http://www.usatoday.com/money/autos/...emiumgas_x.htm

And here's your Mercedes "authority" that you keep pushing down my throat:

Loren Beard, senior manager of Environmental and Energy Planning, for Daimler Chrysler:

http://www.edmunds.com/advice/fuelec...3/article.html

For anyone wondering what the hell's going on, this lkchris character's been harassing me on other sites, because I don't like stealers, and he works for a stealer, and he has been posting shill messages telling distressed new comers with car troubles to give up and take their cars to dealers.

SL2003driver

Oh-No!!!!! Sell it now before the engine blows up.

MilesBFree

My $0.02 is that I will stick with premium.

Using lower octane may probably OK for most of my driving. As others have pointed out, there is probably little danger of detonation and other octane-related issues with the throttle at 50% or less.

However, the danger to the engine is more likely to be seen at WOT, e.g.- when some clown decides to try to force his car into the space as is already occupied by my car (ignoring the laws of physics which state that only one body can occupy a space at any one time), and I have to use full throttle to get out of his way. Or I have to really accelerate to hit a gap in heavy traffic when merging onto the highway.

There are just too many situations where it would be nice to / necessary to use full throttle, and using premium will optimize chances of no engine issues.

gsrjc

Premium for me all the way.

jsap

I use premium, too. But, I have in the past filled up with maybe a dozen tanks full of 87, drove with WOT, and no troubles.

However, that was before 2010. On January 1, 2010, California removed the restriction that kept ethanol levels at 5.7%. So the limit is now 10%.

These premium vs non discussion always ends up with a bunch of people raising their voices and rolling up their sleeves. So, I'm trying to understand WHY Mercedes says premium is necessary on their knock-sensor equipped vehicles, despite that fact that NO trade group or engineering society says it would be dangerous if you used lower octane on engines equipped with knock-sensors.

The answer, I believe, is in the ethanol content. In 1996, when my vehicle was produced, Mercedes's owner's manual approved the use of ethanol up to 10%, along with the 3000 RPM warning if using lower octane gas.

So, that's where the confusion lies. At higher RPM's, the knocking is reduced due to better mixing in the chamber. That why at above 2000 RPM the ignition and variable cam timing is advanced on the M119. So, knocking (detonation) is NOT the reason why Mercedes is recommending lower RPM with lower octane gas.

To have a useful discussion, we need to understand the knock sensor operation. The knock sensor is a passive device that sends a signal (by way of voltage fluctuations) to the appropriate processor. As knocking is observed, the ignition timing is delayed, and advanced incrementally until knocking is present again, and finally delayed slightly. This process keeps the ignition timing as advanced as possible.

However, should the knocking never go away, the process causes the ignition to be delayed to a limit. Once this threshold is reached, OBDII will report a code, and the CEL will be on. This has never happened to me using 87 octane. And, it should NOT happen the HIGHER the RPM.

But, enters ethanol.

Ethanol gas is highly knock resistant. However, at higher RPM and load, the manifold pressure increases. Under pressuress approaching and greater than 100 kilopasacals, the ethanol becomes prone to pre-ignition. Furthermore, as ethanol degrades quickly, within weeks, the gas in your tank will be lower octane, which will also create a greater chance of pre-ignition.

This is consistent with Mercedes' warning that RPM should be kept below 3000 (later revised to 2000) and throttle be kept below 2/3 (to reduce load).

There is, however, the possibility the you could use lower octane safely. By going cooler on the spark plug range and by reducing the electrode gap, you reduce the chances of pre-ignition.

I hope that these discussions in the future will be more fact based, rather than simply reading out of manuals. The manual will say what is the most conservative position Mercedes will take to limit their liability. But there is no reason why you couldn't try to spark plug tune Mercedes like any other car on the planet, including MUCH more expensive makes than Mercedes.

MilesBFree

My concern with knock sensors is that they respond to the occurrence of detonation, not prevent it. So if the detonation is damaging the engine, it is already too late. In some engines, any detonation is too much detonation.

My concern with colder plugs is that they can foul easier.

Most of my experience in plug heat range selection is looking at hotter plugs as part of increasing engine performance, so we are sort of out of my area of expertise. Lowering octane is usually the opposite of what I have done (Avgas purple, anyone?).

jsap

Well, others should chime in, but I'm going out for a while, so let me put in a couple more lines here.

Detonation isn't going to damage the engine, unless it's long term. (In fact, the computer NEEDS the detonation event to occur before it can adapt its ignition timing, except in the case where the ignition timing is simply fully advanced.) What kills engines immediately is pre-ignition.

Hotter spark plugs do not improve engine performance, unless it's to treat a fouling plug. Hot and cold spark plugs produce the same intensity of spark, all other things being equal (brand and type).

Before ethanol here in California went to 10%, my spark plugs were ok, a bit too white, but acceptable. Now, after E10, my spark plugs are bone white. So, I went one range cooler. The plugs are still bone white. I think I can go another range cooler.

The cooler spark plug will dissipate the heat from the combustion quicker to the head, and therefore will less likely cause pre-ignition.

Anyway, I'd love to hear other people's comments that are technical in nature. But, please, no more of this arm throwing and comments like "Oh you're so poor you can't afford premium!" We're not in junior high anymore!

QuestExpert

hello,
I recently bought 2010 GLK 350, couple of questions:
How/where to open its Hood?
Its steering is kind of hard and it doesn’t come back to straight (while driving) by itself do i need to take it to MB service center?

Thanks
QE

NYCGLK

MB says you need premium so you get most out of your car, I think it has been mentioned before by ppl who filled up with lower grade that car didn't like it.

The comment that MB is sold all over the world without modification is simply not true. Why do you think so many cars from europe never make it to US or make it a year later? Why do you think we don't have diesels widely available?

Who cares what 1996 manual said, in 1996 3.5 engine didn't exist and 3.2 made only 215 hp, times changed and engines evolved. 3.5 liter engine today makes over 300hp in SLK.

My common sense tells me that no damage will happend to MB by putting non-premium gas, but why do it in first place? What's the purpose other than to save money? So next question is why spend extra thousands and then try to save pennies?

SL2003driver

Take it by the dealer, sounds like an alignment and they can show you how to open the hood while you are there. In the mean time whatever you do don't put low octane gas in your car.

NYCGLK

What's your previous car?
If you are used to FWD cars, GLK is quite different, it doesn't self center nearly as much as FWD cars do.

jsap

You're twisting my comments. The models sold in various parts of the world are nearly identical, except for certain localizations (imperial dials, NHTSA requirements, radios, etc...). However, the engines are mechanically identical. Ignition maps are altered for various local fuels, but that's about it.

Btw, do you think that GM launches new models in Japan the same year as here? You always launch new models at home turf.

You're not really getting the point. M119 engines were in production since the 1989, and by the mid-90's, 11:1 5.0L versions were in service. This gas discussion is for all cars Mercedes has made.

Your common sense is very mistaken. Common sense ought to dictate that lower octane should be fine in a knock-sensor-equipped vehicle, and that things get even safer at high RPM's.

Contrary to common sense, Mercedes is suggesting that you do not exceed 2000 RPM.

I don't see how you and I could ever discussion octane ratings, if you just don't get the point. The point is NOT how many pennies you can save, or how much you admire your current GLK, or how well you can read your manual. The point is, there is something very non-common-sensical with regards to Mercedes and their 2000 RPM limit. To come to any progress with this discussion, you have to engage the discussion with a technical sensibility, and not with hyperbole.

MilesBFree

I would tend to disagree with the statement that detonation does not cause damage in the short term. I agree it is unlikely at low RPMs and loads. At very high RPMs, the shockwave from the detonation can break pistons. The insulators of the plugs can also break under detonation, sending pieces through the engine and breaking a lot of other components. (Bending of valves, often attributed to detonation, is usually due to other causes.) Almost any detonation will kill a Wankel (rotary) engine as it breaks the apex seals and the engine is toast.

As you pointed out, mild detonation may be less immediately damaging, but the damage does add up over time.

I think I would also disagree that the M-B engineers that designed the ECU and engine want the engine to detonate in order for the ECU to learn how to adapt the timing. Most ECUs use maps as a base for AF mixture, which are used along with airflow sensors and O2 sensors, upon which readings the ECU adjusts the mixture and timing.

The knock sensor is used by the ECU to determine if detonation is occurring, and if so it temporarily retards timing (i.e.- to avoid detonation, not to use it to control timing).

On the ECUs I have seen, this is not a learning / adapting mode; it is a near real-time retard to avoid engine damage from detonation. i.e.- the ECU is not learning / adapting, it has a pre-programmed frequency to which the knock sensor responds. That doesn't change, so there is no adapting. It is there as a fail-safe in case of conditions which can cause detonation, such as too low octane fuel. It is not there for the engine to learn how to set the timing.

I haven't messed with aftermarket ECUs in years, but the older ones I have seen are programmed by a tuner on a dyno to achieve maximum power but also specifically to avoid detonation. The plugs are checked during the dyno runs as well, to determine if detonation is occurring, the AF mixture is too lean, too rich, etc. The mechanics and tuners with whom I have worked take great pains to eliminate detonation (see discussion above on immediate damage from detonation).

But all of that is beside the main point:

In this discussion, we are debating whether or not to use the fuel that has more potential for performance (i.e.- higher octane). Unless there is any argument against wanting the engine to perform up to its potential, I would trust the M-B engineers to specify the proper plugs to work with the fuel they have specified.

Another benefit to higher octane fuel is it does not burn at as low a temperature as does lower octane fuel. Thus it is more resistant to detonation.

So higher octane fuel offers potential for better performance and better detonation protection.

I think that the technical explanation of lower octane fuel and colder plugs is correct; I just don't see why anyone would want to go in that direction.

Exactly. Go with premium, use the stock spark plugs, and enjoy!

jsap

No, it's MORE likely at low RPM's. The air and fuel mixture enters the chamber, but at low RPM's, the mixing is less complete.

It's not just Mercedes engineers. Knock sensor operation requires the ignition timing to be advanced to the point of light detonation, and then pulls back.

The real-time aspect is by the fact that the ECU is constantly reading the knock sensor output. On an 8-cylinder, at, say 3000 RPM, the knock sensors are providing data for 200 combustions per SECOND. The response by the computer is almost immediate to the human senses.

Btw, as you know, detonation is not an ON/OFF thing. The knock sensor is sensitive enough that even the slightest detonation is detected. If the computer does not advance ignition timing to the point where detonation is just beginning to be noticeable, then the computer has absolutely NO basis for where the timing advance ought to be. It would simply be guessing, and, the safest position would then be to full retard. That is just not the case. Furthermore, full retard throws a code.

To avoid what you refer to as "immediate damage" from detonation, yes, the computer will retard a preset amount initially. But, again, it has to advance and hit a slight detonation event in order to find the sweet spot. Btw, this is done on a cylinder by cylinder basis. And, depending on the engine model, the knock sensor data is tied to O2 sensors and not.

However, light detonation is harmless. The most important danger is pre-ignition.

I can see why these discussions are so difficult to do in these benz forums; because technical aptitude is sparse, hyperbole free and infinitely abundant, and when technical aptitude is measurable, misconceptions fill in the rest. Hence, we can't even get started on the core issues.

SL2003driver

what you talk about i know all kind tackneecall stuff

NYCGLK

Huh? Isn't this what you are trying to prove here that using lower grade would be fine?

Of course they are MECHANICALLY identical (3.5 liter V6), however, air quality standards are different in US and Europe so is gasoline, so engines do differ. To what extent? that I don't know. Also how about the whole octane rating to begin with? That hasn't been mentioned, in Russia premium is 95-98 not 91-93.

fine

MilesBFree

Wrong. Timing is defined in the maps in the ECU. The maps are essentially arrays or grids of numbers for timing based on engine RPM, load, etc. There are timing maps, AF maps, and possibly other maps based on how sophisticated the ECU is. The ECU may have separate maps for different octane ratings, etc. (The maps are also referred to as LUTs, or Look Up Tables, since the ECU looks up the appropriate timing based on, for example RPM and load.)

This is how the ECU sets timing, and is why the ECU is not simply guessing.

Data from various sensors including O2, airflow, etc. are used to modify the data read from the maps in near real-time. In the case of an AF map, data coming from the O2 sensor is used to modify the numbers read from certain regions of the map (see image below). This is known as closed loop mode (as in: feedback loop). Open loop mode is where the ECU is using the data straight off the maps without modification based on the sensors' data.

(Note: The maps are not changed in permanent memory. The ECU does a lookup on them and then massages the data to change the timing. The data in the map is not overwritten.)

It seems as if you are asserting that the knock sensor is used in closed loop mode to modify the timing map in the M-B ECU in real-time. I hope to learn something from this discussion, so if you can provide specific examples of the knock sensor being used to modify timing in closed loop mode on a Mercedes I would be very interested in seeing those, as I am not aware of any that work this way. I have seen aftermarket racing ECUs and knock controllers that do this, but wasn't aware the factory M-B ECU did.

Here is an example of a timing map:





Most engines I have seen have one (or at most 2) knock sensors, so how does it monitor each cylinder separately? Does the GLK engine have one sensor per cylinder?


Can you elaborate on how the knock sensor data is tied to an O2 sensor? the knock sensor in effect listens for frequencies associated with knock, and the O2 sensor looks for... O2.


I find that statement to be fairly insulting. Especially since you keep going on about not being able to have a discussion - this sort of deliberately provoking comment makes it hard to do so.

MilesBFree

Deleted.

MBRedux

bigben320e

How about...just use the recommended octane for your vehicle. This subject has been brought up too many times on this forum, and it gets all **** and technical, which is not needed. Use what is recommended, and if you run anything less that is your risk.

MilesBFree

Yes.

jsap

Hey, did you just slap me?

Nothing like a good intermission.

But, I don't know exactly how to respond to this, because it's almost as if you are I are in separate conversations. The labor it would take to respond to your questions is so daunting, I almost need to hear more inflammatory comments to get me fired up. And even that might not be enough, because I've been building up resistance from several ridiculous online conversations lately.

We'll see; maybe later.

MilesBFree

I smell an Internet troll.





Hey Ignatius,

"When a true genius appears in the world, you may know him by this sign, that the dunces are all in confederacy against him." --Jonathan Swift

If you have read your John Kennedy Toole, you will know that that is meant sarcastically, but I wanted to make sure...


If you knew anything about fuel injection and ECUs, it would be pretty simple to answer them.


I had deleted the following, since I wanted to keep the conversation on a civil level and to the point. But since you are trolling and insulting everyone who is interested in having an intelligent conversation about octane, ECU control, etc., here goes:

Your post on this forum indicated that you didn't know what a spark plug is, how to count them, or where they are located on an engine:

https://mbworld.org/forums/sl-class-...do-i-have.html

Your post also indicates that you don't know what your car's model name indicates, i.e.- SL500 by definition means a 5.0 liter V8, and 8 cylinders on that engine means 8 spark plugs. You didn't even have to know what a spark plug was or how to count! Do you know anything about Mercedes-Benz cars?

I am not sure why I am wasting my time on a troll who doesn't know what a spark plug is or what car he is driving...

Anyone have a can of troll-be-gone?


How's that?