Fuse Pull: Low Octane Fuel Fix For L99 and LS3. Reset Fuel Map for High Octane Fuel.

[Higgs Boson]

Originally Posted by E.T.

I think this was posted a while back, but there actually is a TSB for this, so GM is aware it's a problem. I just don't think they released any official solution for it, or a way to prevent it from happening in the first place.

http://www.camaro5.com/forums/showpo...postcount=1261

I don't think it says anything about being stuck at an 87 Octane Learn....It just says put 93 in it and reset it. No?

[E.T.]

It doesn't specifically say it's stuck, but if the only cure is putting in 93 and then pulling fuses or reflashing the ECM, then it sounds like that means it won't "fix" itself on its own.

[Higgs Boson]

Originally Posted by E.T.

It doesn't specifically say it's stuck, but if the only cure is putting in 93 and then pulling fuses or reflashing the ECM, then it sounds like that means it won't "fix" itself on its own.

It sounds like customer service to me. If the fix was, "put in some 93 and drive it around until it feels better" was the solution would you be confident and happy something was done about your concern? Service depts have a criteria called "Fix it Right the First Time" not only on their surveys but because it is the right thing to do. It's only right they reset it for the customer so they can peel out of the parking lot.

[E.T.]

That's the problem though. If we could just put 93 in it and the car would right itself, that would be great, but it doesn't work that way. All GM has to do is make it work that way. It shouldn't be so hard. Personally, I don't really care anymore because my car is tuned and this is a non-issue for me. I'm just surprised that more people aren't upset about this. A 40K, 400+ HP performance car that does 0-60 in 7 seconds....that's epic fail in my book.

[Higgs Boson]

Originally Posted by E.T.

That's the problem though. If we could just put 93 in it and the car would right itself, that would be great, but it doesn't work that way. All GM has to do is make it work that way. It shouldn't be so hard. Personally, I don't really care anymore because my car is tuned and this is a non-issue for me. I'm just surprised that more people aren't upset about this. A 40K, 400+ HP performance car that does 0-60 in 7 seconds....that's epic fail in my book.

If it learned up too fast and crappy gas got put in again it would be straight back to knocking.

There is a surprisingly small number of people who love to put 93 in the tank for an extra 10 HP. There are more SS's out there with 87 than any of us might imagine....

[USAF]

Not in my car, only the good stuff for her.

[Eich]

Originally Posted by Higgs Boson

If it learned up too fast and crappy gas got put in again it would be straight back to knocking.

There is a surprisingly small number of people who love to put 93 in the tank for an extra 10 HP. There are more SS's out there with 87 than any of us might imagine....

If the V-8 w/Auto can shut off 4 cylinders in miliseconds and turn them back on again in miliseconds, I would think that modern electronics could do a resonable job of sensing octane and knocking and advance/retard the timing accordingly. Plenty of vehicles have knock sensors that advance/retard the timing to keep performance at a maximum and knock at a minimum.

It's 1 of 2 things:

1. Either there is no problem and the car is properly setting the timing according to octane/knock. And if this is the case, then a fuse pull is advancing the timing further than it should, giving the car some seat-of-the pants extra power for a little while and gradually retarding the timing back down somewhat to match the actual octane and occurance of knock.

2. Or there is a problem and the car simply won't re-adjust to higher octane tables after it's been lowered.

I haven't done the fuse-pull thing yet. But for those of you that have, I wonder if any of you have experienced knock right after doing the fuse-pull and getting on the throttle. If so, that would mean that number one is likely.

[Higgs Boson]

Originally Posted by Eich

If the V-8 w/Auto can shut off 4 cylinders in miliseconds and turn them back on again in miliseconds, I would think that modern electronics could do a resonable job of sensing octane and knocking and advance/retard the timing accordingly. Plenty of vehicles have knock sensors that advance/retard the timing to keep performance at a maximum and knock at a minimum.

It's 1 of 2 things:

1. Either there is no problem and the car is properly setting the timing according to octane/knock. And if this is the case, then a fuse pull is advancing the timing further than it should, giving the car some seat-of-the pants extra power for a little while and gradually retarding the timing back down somewhat to match the actual octane and occurance of knock.

2. Or there is a problem and the car simply won't re-adjust to higher octane tables after it's been lowered.

I haven't done the fuse-pull thing yet. But for those of you that have, I wonder if any of you have experienced knock right after doing the fuse-pull and getting on the throttle. If so, that would mean that number one is likely.

This is exactly what I have said 20 times.

By the way, some knock is not audible. If you can hear it, not good.... From what I usually see, you can hear it when it pulls 7 degrees or more at once. If it pulls 5 or less, you wouldn't even know it was knocking.

[90503]

Originally Posted by Higgs Boson

This is exactly what I have said 20 times.

By the way, some knock is not audible. If you can hear it, not good.... From what I usually see, you can hear it when it pulls 7 degrees or more at once. If it pulls 5 or less, you wouldn't even know it was knocking.

Higgy, what I get from "paragraph 1"...lol...I think you are correct that the high octane setting might cause a knock "if" it were done with low octane fuel still in the system...Don't think it should knock if high octane is present after a fuse pull...

(I think if a driver chooses to use low octane fuel, they probably should not do the fuse pull)...If knocking on low octane (audibly) then a higher octane should be used...

Why it will recognize lower octane, and adjust itself, but not recognize higher octane is the "flaw" in the system.....

[Higgs Boson]

Originally Posted by 90503

Higgy, what I get from "paragraph 1"...lol...I think you are correct that the high octane setting might cause a knock "if" it were done with low octane fuel still in the system...Don't think it should knock if high octane is present after a fuse pull...

(I think if a driver chooses to use low octane fuel, they probably should not do the fuse pull)...If knocking on low octane (audibly) then a higher octane should be used...

Why it will recognize lower octane, and adjust itself, but not recognize higher octane is the "flaw" in the system.....

High octane table is not tuned for E10, it is based on a spec fuel GM uses when it calibrates its ECMs. The timing values in the high octane table are too high for E10 pump gas and will indeed cause it to knock. Every car I have tuned knocks, even at part throttle, on 93 octane pump gas on the high octane table.

If a driver chooses to use a lower octane fuel, the car will knock. The ECM is programmed to learn how much timing it has to pull to alleviate this knock and it will pull it down until it stops to a bottom level (low octane table). It does this by airflow and RPM and engine load. It does not just click the whole table over to a low octane table. This process takes time and it would also take time to reliably increase timing back TOWARDS the high octane table.

The last sentence you made is what I disagree with. It does recognize the absence of knock (not octane). The ECM learns to a highest point where it does not knock, that's all there is too it. Pulling the fuses and putting in 93 will restart the process but the ACTUAL spark timing will not match the high octane table after being driven around a bit. Actual spark will be lower due to knock. Pulling the fuses again will make it feel peppy and powerful and it will again learn down (not as much as with 87, of course).

Now, when you get a tune, the tuner will tune the high octane table to "best power" in all different combos of throttle/load/RPM, etc so that you can indeed run on the high octane map all the time. The high octane map is reshaped for pump gas rather than GM spec fuel and the overall values in the table will be lower, but it should not be pulling timing. The tuner should then make the low octane table the same shape as the high octane table but pull some timing out of it virtually across the board in order to compensate for a tank of bad gas and the like. It is is a straight up race car then the high octane table is tuned to the race fuel of choice and the low octane table should mirror the high octane table. Race gas quality and properties should be much more reliable than stinky pump gas.

The learning criteria of how and when the ECM learns to adjust timing between the tables can also be adjusted, but this is a far less popular change. Hope this helps.

[90503]

Very well written, thanks....just so I understand...(sorry if this is redundant)...but are you saying an aftermarket tune for the octane table is a good thing? Is it risky in any way?....Better to just keep pulling the fuses from time to time?...Not reccomended?....Is there a good reason it would void the warranty?...(and this would just be for street driving purposes)....Thanks again

[Higgs Boson]

Originally Posted by 90503

Very well written, thanks....just so I understand...(sorry if this is redundant)...but are you saying an aftermarket tune for the octane table is a good thing? Is it risky in any way?....Better to just keep pulling the fuses from time to time?...Not reccomended?....Is there a good reason it would void the warranty?...(and this would just be for street driving purposes)....Thanks again

I am not saying the tune is good or bad regarding the timing, you don't have to worry about pulling fuses if you have a tune and a tune does so much more as well....but many feel it will make it hard to retain powertrain warranty should you have a major component fail so....

If I was of the no tune mindset, which I am not of course, I would fill it up with 93/91 and run a tank through, fill it up again with 93/91, pull the fuses and never look back (and always run premium). Yeah it's going to learn to a safe level for the fuel, that's a good thing. Pulling fuses isn't going to void any warranty.

[E.T.]

Here's another brief article on the issue:

http://thehorsepowerjunkies.com/vehi...-model-camaro/

[Higgs Boson]

Originally Posted by E.T.

Here's another brief article on the issue:

http://thehorsepowerjunkies.com/vehi...-model-camaro/

I think the writer of that article may be a bit confused about the difference between fuel and spark....

LTFT set to the low octane table???