Gas Type [Archive] - Chevy Malibu Forum: Chevrolet Malibu Forums

: Gas Type


Misuraca26
03-27-2011, 11:09 PM
Hey guys,
i am wondering about gas type and if different octanes make a difference in engine performance, keeping the engine clean and mpg.
in MI, all the gasses have 10% ethanol and i usually put in 87 because it is the cheapest there... in NE, the 87 has no ethanol and the 89 has 10% but is cheaper than the 87...
my car was made in michigan so im wondering if the car runs best off of the 87 with 10% ethanol, or would the higher octane 89 10% eth make it run best?
or does putting 87 without ethanol make any difference at all?

RalphP
03-28-2011, 04:27 AM
Hey guys,
i am wondering about gas type and if different octanes make a difference in engine performance, keeping the engine clean and mpg.
in MI, all the gasses have 10% ethanol and i usually put in 87 because it is the cheapest there... in NE, the 87 has no ethanol and the 89 has 10% but is cheaper than the 87...
my car was made in michigan so im wondering if the car runs best off of the 87 with 10% ethanol, or would the higher octane 89 10% eth make it run best?
or does putting 87 without ethanol make any difference at all?

The only way to tell for sure is to run about 10 tanks sequentially of each time through the car, keeping a track of the total gas and mileage over the ten tanks.

HOWEVER - as a general rule, 10% ethanol drops your gas mileage by about 8 to 9% because, strangely enough, ethanol is NOT a fuel, but an oxidizer. On both my Malibu and the Cougar, it's good for 10% extra to go No-Ethanol in my cars.

The OTHER thing is, how well the car runs on 87 octane. Both of mine are happy on it, but technically the Cougar is supposed to require 89 octane (I might have to shift to 89 octane this summer - now that the O2s are replaced and it's running closer to no-longer-rich.)

RwP

Silver LTZ
03-28-2011, 03:32 PM
You have a 3.6 according to your sig. You should be running mid grade as per the owners manual. Regular will pull timing and you will lose some power. The timing is octane, not ethanol based.

Sandhopper
03-28-2011, 06:31 PM
I run 86 octane and don't seem to notice any performance difference when I use mid or premium grades. I might get an extra mile or two per gallon increase in economy from the Premium. All the gas out here now has 10% ETOH so that does hurt the economy a little more. I am getting on average 25-28 mpg depending on mix of city to hwy driving.

TMoneyR523
03-28-2011, 07:45 PM
I have the 3.6L V6.. I always use octane 89 or 93.

DrivenDaily
03-28-2011, 08:35 PM
I try to stay away from ethanol in the fuel. It gets worse mileage and is corrosive.

I found on both my V6's that 87 runs worse (performance and mileage) than 89, and 91 or higher doesn't seem to yield better mileage or extra horsies under the hood.

I almost always use top-tier gasolines instead of Thornton or Kroger or Mom-n-Pop. Costs a little more now but I get slightly better mileage and a cleaner engine, so it pays down the road.

budman65
03-28-2011, 11:00 PM
I've always ran 87 octane with no issues. I'll give the higher octane a try sometime and see if I can tell a difference with my V6?

Lgndryhr
03-29-2011, 01:08 AM
I've run four different octanes in my car. I've run 87, 89, 91, and 93. I noticed a big difference between 87 and 89. The difference between 89 and 91 was not very big. I do notice a big difference in the use of 93, which is what I use in my car from Shell. My previous I used the octane of gas that gave the best overall performance and efficiency. This time around my LE5 seems to like 93 so she gets what she wants. No clue what previous owner put in her before me.

DrivenDaily
03-29-2011, 04:27 AM
I haven't found 93 yet. If I do I'll see about going through a few tanks of that to see how it goes. Great idea! Thanks.

RalphP
03-29-2011, 06:33 AM
What I'm about to type may have absolutely zero relevance to the Malibu ECM programming, but it's something worth considering.

Back when the emissions stuff was just getting started good. Chrysler did something called "LeanBurn" (and GM did also, but I forget what they called it - the '82 Skylark we drove for a while with the V6 did this also!) where it would keep leaning out the motor and advancing the spark until it started to ping or knock, then it would enrich the mix and retard the spark.

With that, the higher the octane, the better the gas mileage.

My 2000 has a knock sensor - don't know what all it does for the car in programming the ECM, however, so take this with a LARGE bag of salt :D

But that would explain how a higher octane gas gives better gas mileage. Since the octane has NO effect on gas mileage past the knock resistance - and with higher octane, you can run leaner and with more spark advance, both of which help gas mileage.

It'd be nice if someone who knows how the ECM is programmed (i.e., a tuner) could say if I'm right, or if I'm just blowing smoke up here ...

Again, I have NO idea if this is applicable to the current Malibus or not. This used to be done by GM and Chrysler, though, so ...

RwP

whoflungpoo
03-29-2011, 08:31 AM
i have a 2005 malibu ls with the v6, it has NEVER seen anything but 93 or 91 octane(depends which gas station im at) still running at 180,000 miles...

my .02 :P

Lgndryhr
03-29-2011, 10:07 AM
The only place that has 93 octane in my area is Shell and BP. I'm not sure about BP's gas (will ask my dad), but the Shell stations here have a max of 10% Ethanol in all the gas :( The rest of the places around here have started to follow suit so I cannot escape it sadly. I wish I could put gas without Ethanol in my tank.

Edit: Also, I read somewhere and have heard from my ex-GM employee friend that the LE5 (ecotec 2.4l) can burn 87 or higher due to the program able to detect octance and adjust accordingly. He did say though the LE5 is made to use 91 or 93 octane for best performance. I need to find the site on here that also said that. I will search around and post it on here when I find it.

Edit 2: So the article I was talking about was for the LE5 engine, but it was for the ones that were turbo'd or SS. My mistake. I am still going to use 93 octane based on how each performed for me.

Silver LTZ
03-29-2011, 06:24 PM
I haven't found 93 yet. If I do I'll see about going through a few tanks of that to see how it goes. Great idea! Thanks.

Won't do anything. Car is programed to run on mid grade 91 best. Running lower will effect timing, running higher without a tune won't do anything.

DrivenDaily
03-30-2011, 04:10 AM
Won't do anything. Car is programed to run on mid grade 91 best. Running lower will effect timing, running higher without a tune won't do anything.

Help me out a little, then, please. Around here I've seen 3 grades of gasoline and the octanes are 87, 89, and 91. I've seen 93 elsewhere but I'll have to look to see if it's even around here.

What really is mid-grade? My owner's manual says that 87 will run, but 89 is preferred. And on my '09 I learned that 91 didn't net any performance or mileage gains. I assume that 93 won't either. Is that right?

Also, if 89 (which is all I put in right now) starts to be available blended with ethanol but the 91 isn't, I just might start using 91 just to stay away from ethanol, and to thwart the reduced mpg's from ethanol.

What do the octanes run down there in sunny, warm Florida?

Silver LTZ
03-30-2011, 06:23 PM
Help me out a little, then, please. Around here I've seen 3 grades of gasoline and the octanes are 87, 89, and 91. I've seen 93 elsewhere but I'll have to look to see if it's even around here.

What really is mid-grade? My owner's manual says that 87 will run, but 89 is preferred. And on my '09 I learned that 91 didn't net any performance or mileage gains. I assume that 93 won't either. Is that right?

Also, if 89 (which is all I put in right now) starts to be available blended with ethanol but the 91 isn't, I just might start using 91 just to stay away from ethanol, and to thwart the reduced mpg's from ethanol.

What do the octanes run down there in sunny, warm Florida?

"Mid-grade" is at least 89. In FL, and when I was in NY it was 87, 89 and 93. Some Sunocos down here have 94 too, but it is like .25 more a gallon. I run 93 in all three cars. The wife's can run on mid, the others need premium.

DrivenDaily
03-31-2011, 04:14 AM
Cool, thanks! Last night I went to a Shell to fill up and guess what I discovered? They now have 87, 89, and 93. The 93 was 12 cents more but I still filled with 89. Do you think I could realize any benefits from using 93, even if it's only long-term?

Lgndryhr
03-31-2011, 09:17 AM
I personally believe it gives me a piece of mind at least with using octane 93. As far as long term benefits, I'm not sure there. Some people say yes, some say no, and some say they don't know lol. I hear mostly from car enthusiasts either 93 helps fuel lines and such or I hear just run what the manual says.

Silver LTZ
03-31-2011, 06:19 PM
Cool, thanks! Last night I went to a Shell to fill up and guess what I discovered? They now have 87, 89, and 93. The 93 was 12 cents more but I still filled with 89. Do you think I could realize any benefits from using 93, even if it's only long-term?

In the old days, yes. Now with all the ECU programing there is nothing to gain by using higher then recommended. Just do not use lower, stick with 89.

cp-the-nerd
04-05-2011, 09:32 PM
I've always used BP 93 octane. To answer someone's previous question, BP gas quality is among the best, used to be Amoco.

I'm under the impression premium/high grade gas has more additives that keep the engine running factory clean. The way I see it, the good stuff only costs $1.40 more per fill-up over mid grade, so why the hell not.

wjjeepman34
06-13-2011, 08:08 AM
To prove that octane rating does not give you better gas milage (or performance with a stock tune). Pure ethanol has an octane rating of nearly 100, and E85 is 94-96.

http://en.wikipedia.org/wiki/Octane_rating

Don't forget to reference the far right hand column, that is the method that the gas at the pumps are calculated.

The thing with octane is that it allows you to create more horsepower, it gives you the ability to advance timing, raise your compression on the motor, or raise/add boost psi on a turbo/super charger, since all octane is is resistance to knock, which is what will happen if you run too low of octane for your timing, compression, psi on any given vehicle. I can go more and more on the subject, but for a stock malibu (and almost all stock vehicles out there), whatever the company recommends for the vehicle is best, you wont get any more milage/horsepower out of it unless you do some or all of said modifications.

MalibuKen
06-13-2011, 11:50 AM
I'm under the impression premium/high grade gas has more additives that keep the engine running factory clean. The way I see it, the good stuff only costs $1.40 more per fill-up over mid grade, so why the hell not.

If it makes you happy, by all means keep doing it.

The truth, however, is that the extra money is a complete waste.
It is only "good stuff" in an engine that needs the higher octane.
Oh, and it's good for the oil company too. ;)

In some engines, the higher octane fuel is actually worse; lower power and worse mileage. Then there is the increased chance of getting "bad" gas because the turn over in the premium tank is longer. At some stations, it's MUCH longer.

DrivenDaily
06-13-2011, 02:17 PM
Premium grade gas is only higher octane. Go to a Shell station and you'll notice that their additives are in all grades. Premium around here is 92 or 93 octane, mid is 89, low is 87. My manual says to use 87, or for improved performance use 89. I've tried 93 and it made no significant difference in mileage (I keep records) or power (butt dyno). So I use 89 for the best performance and save the dough.

hondafanatic17
06-30-2011, 05:01 PM
What I'm about to type may have absolutely zero relevance to the Malibu ECM programming, but it's something worth considering.

Back when the emissions stuff was just getting started good. Chrysler did something called "LeanBurn" (and GM did also, but I forget what they called it - the '82 Skylark we drove for a while with the V6 did this also!) where it would keep leaning out the motor and advancing the spark until it started to ping or knock, then it would enrich the mix and retard the spark.

With that, the higher the octane, the better the gas mileage.

My 2000 has a knock sensor - don't know what all it does for the car in programming the ECM, however, so take this with a LARGE bag of salt :D

But that would explain how a higher octane gas gives better gas mileage. Since the octane has NO effect on gas mileage past the knock resistance - and with higher octane, you can run leaner and with more spark advance, both of which help gas mileage.

It'd be nice if someone who knows how the ECM is programmed (i.e., a tuner) could say if I'm right, or if I'm just blowing smoke up here ...

Again, I have NO idea if this is applicable to the current Malibus or not. This used to be done by GM and Chrysler, though, so ...

RwP

Anyways before I start my rant, I run 89 in my '10 Malibu. Its cleaner, makes me feel better about how I'm treating my car and its only 10 cents more a gallon than 87 so whoopee!

Back to clarifing what your saying. Yes what your saying is correct. The first cars to actually do this was suprisingly Saab. Thats why I know something about it. Saab used this technology and greatly improved it. Basically we will take my Saab for example a 1997 Saab 9000 Aero with high pressure Mitsu turbo. My car asks to be run on 91 or greater octane for best performance. But it doesn't have to. If it is ran on lower than 91 the ECU adjust the timing on stuff in the engine and fuel mixture ratio for the lower octane. So that you can run it safely in the car on lower octane, but the performance will not be as great. I know that if I run lower gas it will not hurt my car. I just wont have all the power I did on 93. So all in all yeah that is how it works for cars that have octane ratings on them. Go with the rating you will have the best performance, go lower there will be no harm to it just won't be giving the engine all that it can do. Cars that don't have a rating. I doubt it helps with gas mileage, really I do. Just keeps the engine cleaner, which shouldn't we all try to keep are cars going as long as they can?

Lgndryhr
07-26-2011, 05:36 PM
Was talking to my dealer today. He said it's not bad to run a tank of premium every once in a while, but didn't recommend it because it could cause the piston to burn a hole due to it keeps pushing the engine to ping. This eventually leads to engine pushing too hard or leaning I guess you could call it. After doing some more research, I am switching to 87 octane. My 2.4l LE5 Ecotec can't benefit form the 91 or 93 octane without a tune essentially. HPTuners can tune my car, but I don't know if I should even do that. Also, my manual says 87 or higher is okay. I read some say it's okay, some say not to, and others say it doesn't matter. I'll try 87 for a little while and see.

MalibuKen
07-26-2011, 06:55 PM
Was talking to my dealer today. He said it's not bad to run a tank of premium every once in a while, but didn't recommend it because it could cause the piston to burn a hole due to it keeps pushing the engine to ping.

And he got his mechanics training from the Monty Python school of auto mechanics, right ?? :eek:

All that would be funny if it wan't so pathetically wrong.
I strongly encourage you to not believe anything "he" says in the future.

There is nothing "better" about so called premium gas. NOTHING.
It isn't cleaner, it doesn't have "more energy" and it doesn't run cooler....or hotter either. It simply ignites a tiny bit slower for engines that have high compression and tend to ignite the fuel just from the compression alone (diesel effect).

"Your dealer" has it exactly backwards. If you have a high compression engine and the octane rating of your fuel is not high enough, all kinds of engine damage can result from the pre-ignition knock (premature explosion)......including holes in the pistons.

The only thing premium about "premium" gas is the price.

Lgndryhr
07-26-2011, 08:25 PM
And he got his mechanics training from the Monty Python school of auto mechanics, right ?? :eek:

All that would be funny if it wan't so pathetically wrong.
I strongly encourage you to not believe anything "he" says in the future.

There is nothing "better" about so called premium gas. NOTHING.
It isn't cleaner, it doesn't have "more energy" and it doesn't run cooler....or hotter either. It simply ignites a tiny bit slower for engines that have high compression and tend to ignite the fuel just from the compression alone (diesel effect).

"Your dealer" has it exactly backwards. If you have a high compression engine and the octane rating of your fuel is not high enough, all kinds of engine damage can result from the pre-ignition knock (premature explosion)......including holes in the pistons.

The only thing premium about "premium" gas is the price.

You just re-said what I said from my dealer. He never said it was best to use. Please re-read my post. Also, premium has more additives and runs better in high performance cars. That's about it.

DrivenDaily
07-27-2011, 04:38 AM
Premium won't cause the piston to burn a hole (quoting your quote of the SA). Higher octane that can't be used by the engine is just a waste of money but it will never hurt the car.

Lower octane has less power, ignites more easily (ping, knock, predetonation, etc.), and CAN hurt an engine if it isn't tuned to use it.

Your choice on what octane to use, but lower octane will result in less performance and possibly less mileage. Check your numbers on the cost per mile and then make your final choice on what to buy.

I use 89 in my V6. It has more power, mileage, and performance than 87 and costs less per mile than 93, which doesn't seem to offer more performance in my engine.

MalibuKen
07-27-2011, 07:02 AM
You just re-said what I said from my dealer.

No I didn't.

Maybe you thought that's what you said but it came out backwards.

You said that HE said that premium gas can damage an engine that doesn't need it.........and that is just NOT true.

Lgndryhr
07-27-2011, 07:36 AM
He told me higher octane than what the manual says can damage an engine because he has had cars come in with pistons that burned a hole due to the engine kept trying to ping itself using the higher octane gas. And due to pushing the piston harder and harder it got hotter and hotter until it burned a hole.

I will admit I have a hard time believing him. Since I have tested each octane in my car with tank fulls of each and 93 gave me the best MPG's and performance. When I ran 87 I felt a lag in the car, when I ran 89 it ran a little better in performance but got lower MPG's, and in 93 it feels like I get better performance and my MPG's are higher. I may give 87 another shot for a few tanks and see.

Malo83
07-27-2011, 01:05 PM
I've always ran 87 octane with no issues. I'll give the higher octane a try sometime and see if I can tell a difference with my V6?
I was running 89 but switched back to 87 with no loss of power or performance, the LTZ runs great with the 87 ;)

DrivenDaily
07-27-2011, 04:43 PM
I was running 89 but switched back to 87 with no loss of power or performance, the LTZ runs great with the 87 ;)

I'm sure yours does, but I also think we should note that there's a difference between the I4 and the V6.

The V6 that I have, and the one I had in my '09 2LT, both run/ran better on 89 than 87, and neither one gained any perceptible performance or mileage on 91 or 93.

If the I4 runs fine on 87 and gains nothing on 89 then it would be money saved to buy 87.

MalibuKen
07-27-2011, 05:11 PM
I will admit I have a hard time believing him.

And what I was trying to say somewhat diplomatically is:
You should have a hard time believing it...... as it is TOTAL BS.

DrivenDaily
07-27-2011, 05:29 PM
And what I was trying to say somewhat diplomatically is:
You should have a hard time believing it...... as it is TOTAL BS.

^^ +1

I was thinking about this on my way to work and back home today. I just kept shaking my head about it. WHERE on Earth did that jerk get his info? Some people speak just hear themselves talk, and that guy seems to fit the bill!

Lgndryhr
07-27-2011, 07:13 PM
Haha, it's cool guys. I appreciate the input. I thought about it too. I had a hard time believing that. I've yet to ever have that happen on any of my cars, my family members' cars, or my friends' cars.

08chevymalibultz
07-27-2011, 07:52 PM
Federal Trade Commission Protecting America

The Low-Down on High Octane Gasoline
Are you tempted to buy a high octane gasoline for your car because you want to improve its performance? If so, take note: the recommended gasoline for most cars is regular octane. In fact, in most cases, using a higher octane gasoline than your owner's manual recommends offers absolutely no benefit. It won't make your car perform better, go faster, get better mileage or run cleaner. Your best bet: listen to your owner's manual.

The only time you might need to switch to a higher octane level is if your car engine knocks when you use the recommended fuel. This happens to a small percentage of cars.

Unless your engine is knocking, buying higher octane gasoline is a waste of money, too. Premium gas costs 15 to 20 cents per gallon more than regular. That can add up to $100 or more a year in extra costs. Studies indicate that altogether, drivers may be spending hundreds of millions of dollars each year for higher octane gas than they need.

What are octane ratings?
Octane ratings measure a gasoline's ability to resist engine knock, a rattling or pinging sound that results from premature ignition of the compressed fuel-air mixture in one or more cylinders. Most gas stations offer three octane grades: regular (usually 87 octane), mid-grade (usually 89 octane) and premium (usually 92 or 93). The ratings must be posted on bright yellow stickers on each gasoline pump.

What's the right octane level for your car?
Check your owner's manual to determine the right octane level for your car. Regular octane is recommended for most cars. However, some cars with high compression engines, like sports cars and certain luxury cars, need mid-grade or premium gasoline to prevent knock.

How can you tell if you're using the right octane level? Listen to your car's engine. If it doesn't knock when you use the recommended octane, you're using the right grade of gasoline.

Will higher octane gasoline clean your engine better?
As a rule, high octane gasoline does not outperform regular octane in preventing engine deposits from forming, in removing them, or in cleaning your car's engine. In fact, the U.S. Environmental Protection Agency requires that all octane grades of all brands of gasoline contain engine cleaning detergent additives to protect against the build-up of harmful levels of engine deposits during the expected life of your car.

Should you ever switch to a higher octane gasoline?
A few car engines may knock or ping - even if you use the recommended octane. If this happens, try switching to the next highest octane grade. In many cases, switching to the mid-grade or premium-grade gasoline will eliminate the knock. If the knocking or pinging continues after one or two fill-ups, you may need a tune-up or some other repair. After that work is done, go back to the lowest octane grade at which your engine runs without knocking.

Is knocking harmful?
Occasional light knocking or pinging won't harm your engine, and doesn't indicate a need for higher octane. But don't ignore severe knocking. A heavy or persistent knock can lead to engine damage.

Is all "premium" or "regular" gasoline the same?
The octane rating of gasoline marked "premium" or "regular" is not consistent across the country. One state may require a minimum octane rating of 92 for all premium gasoline, while another may allow 90 octane to be called premium. To make sure you know what you're buying, check the octane rating on the yellow sticker on the gas pump instead of relying on the name "premium" or "regular."

For More Information
If you're concerned about the accuracy of an octane label - or if you don't see a yellow octane sticker on a gasoline pump, write: Consumer Response Center, Federal Trade Commission, Washington, DC 20580.

The FTC works to prevent fraudulent, deceptive and unfair business practices in the marketplace and to provide information to help consumers spot, stop and avoid them. To file a complaint or get free information on consumer issues, visit ftc.gov or call toll-free, 1-877-FTC-HELP (1-877-382-4357); TTY: 1-866-653-4261. Watch a video, How to File a Complaint, at ftc.gov/video to learn more. The FTC enters consumer complaints into the Consumer Sentinel Network, a secure online database and investigative tool used by hundreds of civil and criminal law enforcement agencies in the U.S. and abroad.

October 2003

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Website Policies Accessibility Privacy Policy Browser Plug-ins Related Sites USA.gov For FTC Staff Last Modified: 24 April 2009



Note: I thought this would be helpful to some! I run 87 from Shell and get no pings / knocks from my 3.6L V6 Malibu but one of these days, I will try a higher octane to see if there is any improvement!

DrivenDaily
07-28-2011, 03:19 AM
Thanks, 08!

Accurate information is always welcome, especially when it has been put together so concisely.

The owner's manual for the 3.6 says you can use 87 or 89. If you use 87 the computer is supposed to detect it and modify the tuning accordingly, so you might see slightly better performance and maybe even mileage. But like the article says, some engines might not respond like the average one.

Oncewasarental
08-16-2011, 08:43 PM
Well I have a few questions for you all since i am not very educated on the subject... I have the LE9, which is the E85 capable version of the standard LE5, now, one of you stated the E85 is rated at 94-97 octane...I think, and i have used it before and it did SEEM to have better performance, BUT, the mileage was awful. Now, I know that since E85 has less energy than gasoline, it would do that, and the only difference I could find in the two engines is the injectors, the ones for the LE9 are stainless and have a wider cone spray pattern with a higher volume output. That being said, do you think I would benefit from 89 octane more so than someone with an LE5? The quote below was taken from an article in the link that was posted earlier in this thread. I know it talks mainly about the 2.2l, but i think they are trying to say that the 2.4 was developed from that engine..


"E85 Flexible-Fuel Capability (LE9)
GM has led the industry in introducing flex-fuel capability to its cars and trucks, and the new flex-fuel 2.2L I-4 VVT ( LE8 ) extends availability to an even broader range of customers. E85 is a clean-burning alternative fuel made in the United States from corn and other crops, composed of 85 percent ethanol alcohol and 15 percent gasoline. The 2.2L's flex-fuel technology is both sophisticated and durable.

Hardware changes for flex-fuel operation are limited to the injectors. Because ethanol has fewer BTUs (less energy) than the same volume of gasoline, more fuel is required to produce the same horsepower at wide-open throttle. Flex fuel engines use unique stainless injectors with a greater cone angle and higher maximum fuel-flow rate. The fuel rail matches the injectors, but it's manufactured of the same stainless steel used for all 2.2L I-4 fuel rails.


Flex fuel engines require special valves and valve seats to withstand the wear and corrosive effects of ethanol. The nitrided Silcrome 1 intake valves and 21-43 exhaust valves used in the 2.2L I-4 are up to the challenge. Compared to conventional iron-alloy valve material, nitrided Silcrome 1 includes tungsten, vanadium, manganese, silicone and higher chromium content. It is harder, and it improves durability, even under the rigors of ethanol operation. The 21-43 exhaust valves work equally well. Valve seat inserts have been upgraded to premium materials with a high percent of tool steel and solid lubricants resulting in excellent durability whether E85 or gasoline is run in the engine.


The flex-fuel 2.2L doesn't require a special fuel sensor. The first flex-fuel engines used a light-reactive sensor to measure fuel composition from 100 percent gasoline to 85 percent ethanol. The 2.2L has a virtual sensor-software programmed in the E37 ECM with no separate physical sensor whatsoever. Based on readings from the oxygen (O2) sensors, fuel level sensor and vehicle speed sensors, the ECM adjusts the length of time the fuel injectors open for the type of fuel used. Within a few miles after filling up, the E37 controller determines what fuel is powering the 2.2L I-4 and manages the engine accordingly."

Rodents
08-16-2011, 09:06 PM
It'd be nice if someone who knows how the ECM is programmed (i.e., a tuner) could say if I'm right,

RwP

Well, even though this is an ancient thread, Ralph, here you go, the knock sensor system description and operation, for the 3.6 but it's all about the same general idea.

The knock sensor system enables the control module to control the ignition timing for the best possible performance while protecting the engine from potentially damaging levels of detonation, also known as spark knock. The knock sensor system uses one or 2 flat response 2-wire sensors. The sensor uses piezo-electric crystal technology that produces an AC voltage signal of varying amplitude and frequency based on the engine vibration or noise level. The amplitude and frequency are dependant upon the level of knock that the knock sensor detects. The control module receives the knock sensor signal through the signal circuit. The knock sensor ground is supplied by the control module through the low reference circuit.

The control module learns a minimum noise level, or background noise, at idle from the knock sensor and uses calibrated values for the rest of the RPM range. The control module uses the minimum noise level to calculate a noise channel. A normal knock sensor signal will ride within the noise channel. As engine speed and load change, the noise channel upper and lower parameters will change to accommodate the normal knock sensor signal, keeping the signal within the channel. In order to determine which cylinders are knocking, the control module only uses knock sensor signal information when each cylinder is near top dead center (TDC) of the firing stroke. If knock is present, the signal will range outside of the noise channel.

If the control module has determined that knock is present, it will retard the ignition timing to attempt to eliminate the knock. The control module will always try to work back to a zero compensation level, or no spark retard. An abnormal knock sensor signal will stay outside of the noise channel or will not be present. knock sensor diagnostics are calibrated to detect faults with the knock sensor circuitry inside the control module, the knock sensor wiring, or the knock sensor voltage output. Some diagnostics are also calibrated to detect constant noise from an outside influence such as a loose/damaged component or excessive engine mechanical noise.

Rodents
08-16-2011, 09:12 PM
Ralph, while I'm at it, here's ECM control strategy, or some of it, just FYI.

Fuel Metering Modes of Operation
The engine control module (ECM) monitors voltages from several sensors in order to determine how much fuel to give the engine. The fuel is delivered under one of several conditions called modes. The ECM controls all modes.

Starting Mode
With the ignition switch in the ON position, before engaging the starter, the engine control module (ECM) energizes the fuel pump relay for 2 seconds allowing the fuel pump to build up pressure. The ECM first tests speed density, then switches to the mass air flow (MAF) sensor. The ECM also uses the engine coolant temperature (ECT), the throttle position (TP), and the manifold absolute pressure (MAP) sensors to determine the proper air/fuel ratio for starting. The ECM controls the amount of fuel delivered in the starting mode by changing the pulse width of the injectors. This is done by pulsing the injectors for very short times.

Clear Flood Mode
If the engine floods, clear the engine by pressing the accelerator pedal down to the floor and then crank the engine. When the throttle position (TP) sensor is at wide open throttle, the engine control module (ECM) reduces the injector pulse width in order to increase the air to fuel ratio. The ECM holds this injector rate as long as the throttle stays wide open and the engine speed is below a predetermined RPM. If the throttle is not held wide open, the ECM returns to the starting mode.

Run Mode
The run mode has 2 conditions called Open Loop and Closed Loop. When the engine is first started and the engine speed is above a predetermined RPM, the system begins Open Loop operation. The engine control module (ECM) ignores the signal from the heated oxygen sensor (HO2S) and calculates the air/fuel ratio based on inputs from the engine coolant temperature (ECT), mass air flow (MAF), manifold absolute pressure (MAP), and throttle position (TP) sensors. The system stays in Open Loop until meeting the following conditions:

• Both HO2S have varying voltage output, showing that they are hot enough to operate properly. This depends upon the engine temperature.

• The ECT sensor is above a specified temperature.

• A specific amount of time has elapsed after starting the engine.

Specific values for the above conditions exist for each different engine, and are stored in the electrically erasable programmable read-only memory (EEPROM). The system begins Closed Loop operation after reaching these values. In Closed Loop, the ECM calculates the air/fuel ratio (injector on-time) based upon the signal from various sensors, but mainly from the HO2S. This allows the air/fuel ratio to stay very close to 14.7:1.

Acceleration Mode
When the driver pushes on the accelerator pedal, air flow into the cylinders increases rapidly, while fuel flow tends to lag behind. To prevent possible hesitation, the engine control module (ECM) increases the pulse width to the injectors to provide extra fuel during acceleration. The ECM determines the amount of fuel required based upon the throttle position, the coolant temperature, the manifold air pressure, the mass air flow, and the engine speed.

Deceleration Mode
When the driver releases the accelerator pedal, air flow into the engine is reduced. The engine control module (ECM) reads the corresponding changes in throttle position, manifold air pressure, and mass air flow. The ECM shuts OFF fuel completely if the deceleration is very rapid, or for long periods, such as long, closed-throttle coast-down. The fuel shuts OFF in order to protect the catalytic converters.

Battery Voltage Correction Mode
When the battery voltage is low, the engine control module (ECM) compensates for the weak spark delivered by the ignition system in the following ways:

• Increasing the amount of fuel delivered

• Increasing the idle RPM

• Increasing the ignition dwell time

Fuel Cutoff Mode
The engine control module (ECM) cuts off fuel from the fuel injectors when the following conditions are met in order to protect the powertrain from damage and improve driveability:

• The ignition is OFF. This prevents engine run-on.

• The ignition is ON but there is no ignition reference signal. This prevents flooding or backfiring.

• The engine speed is too high, above red line.

• The vehicle speed is too high, above rated tire speed.

• During an extended, high speed, closed throttle coast down. This reduces emissions and increases engine braking.

• During extended deceleration, in order to protect the catalytic converters.

Short Term Fuel Trim
The short term fuel trim values change rapidly in response to the heated oxygen sensor (HO2S) signal voltages. These changes "fine tune" the engine fueling. The ideal fuel trim values are around 0 percent. A positive fuel trim value indicates that the engine control module (ECM) is adding fuel in order to compensate for a lean condition. A negative fuel trim value indicates that the ECM is reducing the amount of fuel in order to compensate for a rich condition.

When the ECM determines that the short term fuel trim is out of the operating range, the following DTCs will set:

• DTC P0171 Bank 1 Too Lean

• DTC P0172 Bank 1 Too Rich

Long Term Fuel Trim
The long term fuel trim is a matrix of cells arranged by RPM and manifold absolute pressure (MAP). Each cell of the long term fuel trim is a register like the short term fuel trim. As the engine operating conditions change, the engine control module (ECM) will switch from cell to cell to determine what long term fuel trim factor to use in the base pulse width equation.

While in any given cell, the ECM also monitors the short term fuel trim. If the short term fuel trim is far enough from 0 percent, the ECM will change the long term fuel trim value. Once the long term fuel trim value is changed, it should force the short term fuel trim back toward 0 percent. If the mixture is still not correct, the short term fuel trim will continue to have a large deviation from the ideal 0 percent. In this case, the long term fuel trim value will continue to change until the short term fuel trim becomes balanced. Both the short term fuel trim and long term fuel trim have limits which vary by calibration. If the mixture is off enough so that long term fuel trim reaches the limit of its control and still cannot correct the condition, the short term fuel trim would also go to its limit of control in the same direction. If the mixture is still not corrected by both short term fuel trim and long term fuel trim at their extreme values, a fuel trim diagnostic trouble code (DTC) will likely result. When the ECM determines that the long term fuel trim is out of the operating range, the following DTCs will set:

• DTC P0171 Bank 1 Too Lean

• DTC P0172 Bank 1 Too Rich

Under the conditions of power enrichment, the ECM sets the short term fuel trim to 0 percent until power enrichment is no longer in effect. This is done so the Closed Loop factor and the long term fuel trim will not try to correct for the power enrichment condition.

MalibuKen
08-17-2011, 06:54 AM
That being said, do you think I would benefit from 89 octane more so than someone with an LE5?

NO, probably not.
What does your owner's manual say ??

Ethanol isn't designed or altered to make it have a higher octane rating, it is just a natural characteristic. Because it will also run on E-10 or E-0, the basic engine design probably calls for plain old "low" octane regular.