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

[RayYork]

Has it been definitively determined if the fuse pull works with the LS3 or do you have to disconnect the battery?

[R8RUtz]

I tried this yesterday, I had put 87 oct on accident like 6 months ago, I wish I would have read this back Then, it totally worked, Very awesome, Car runs alof Smoother now, all I can say is thanks to everyone .. .

[PQ]

Originally Posted by BSR-1

Will every tuner do that? I just was trying not to assume anything.
Sorry if I'm putting out bad info, that was not my intention.

That's one of those 'tuner' things that they never will verify to us. But the ones I talked to said yes. So I can't say every tuner but it seems that way. I've only heard it confirmed. I've never heard it denied. For whatever that's worth. LOL

[PQ]

Originally Posted by RayYork

Has it been definitively determined if the fuse pull works with the LS3 or do you have to disconnect the battery?

I can't imagine why it would be different.

[RayYork]

Originally Posted by PQ

I can't imagine why it would be different.

I can't either but I have read a few times here that you have to disconnect the battery on the LS3; not just pull the fuses.

My stock (3 week old) 2SS RS can spin the tires if I ring it out from a rolling start and turn a corner but it cannot do it in a straight line. I haven't dumped the clutch to do a burnout as I just have nightmares of breaking the tranny. I keep reading where people can do a burnout from a 5MPH start and that it's easy to do just by mashing the gas. Makes me think my car is not generating all the HP that others are.

I've done the fuse pull and it seemed to give it some more guts but I'm still not rippin' the hides off..........

[f5journal]

I've done the pull 3 or 4 times now on my LS3. Each time it "seems" to be noticably better. However, it is always in the morning when cool and then later in the day I decide it did nothing

So as PQ suggested, I did some 0-60mph runs

All were right at 7 seconds +- 2 tenths. BUT, I forgot to turn off the A/C...and it was 98 degrees. None of the runs were perfect, but they were not "try agains". Slight missed shift on one, a little laydown bog on another and a pretty clean one with some tire spin.

I will try again on a cooler morning and see what I have. I think my car is going back to the low octane table soon after pulling the fuses and/or my knock sensors are detecting the weird noise in my engine or exhaust that I spoke to in another thread.

[R8RUtz]

I pulled my fuses for 5 hours, but once I put them backing I did not start the Car for another 15 hours. This definitely made a difference on my L99 motor.

I had put 87 octane in the car like be months ago.

Again all I can say is thanks, and wish I had read this sooner.

[Belle]

So, I read this thread this morning. I pulled the fuses, waited for a few hours and re-installed them.

What a huge difference!

All this time, it felt like something was quite not right. So it was the low octane causing the lack of performance.

I've been using 91 (California) in my car from the get-go. The dealer that I bought the Camaro from must have put 87 and tricked the sensors.

Dang! I almost have 6K on my 2011 SS. I wish I knew about this fix 4 months ago.

Thanks for posting!

[brianko]

Originally Posted by PQ

That's one of those 'tuner' things that they never will verify to us. But the ones I talked to said yes. So I can't say every tuner but it seems that way. I've only heard it confirmed. I've never heard it denied. For whatever that's worth. LOL

Sure they will, if you ask nicely! I don't know about other tuners, but I don't subscribe to the "copy the high octane over the low octane" table theory when I tune a vehicle. (I think one of the tuning books out there advocates this.) The reason why it's a bad idea? The ECM interpolates between the high and low spark tables based upon knock sensor data. Copying the high data over the low data leaves no room for the ECM to interpolate a lower timing value, so the ECM is always pulling timing in response to KS events in the event of low octane fuel. Ideally, the ECM will "back off" of the highest spark value for a given engine load/RPM to compensate for KS events, then refer to the interpolated values for the remainder of the tank until you refuel.

Personally, if I'm tuning any GM that supports dual octane tables, I tune based upon the octane range the customer will be running. An 87/91 dual octane tune will require fewer changes to the low octane table than, say, a 91/93 tune. But blindly copying the high table over the low table isn't doing the customer any favors.

Strangely, the "LS1"-style PCMs (2006 and before) had no problems with adjusting for octane: Fill up with more than 6 gallons of fuel, and the PCM reset itself to read from the high octane spark table, adjusting for knock events after startup. Works very reliably.

The E38 computer in our vehicles *should* operate the same way (otherwise, the ECM would never adjust for octane changes), but it doesn't appear to do so. Whether it's a quirk in the GM programming or a deliberate change remains to be seen, as I've not seen any GM engineers step forward with an explanation (and I doubt they will). I've done back-to-back pulls on my dyno and it does appear the ECM seems to "lock in" to the low octane table, requiring a fuse pull to reset to the high octane table. Maybe GM will fix this in a future calibration update.

[ss/rs-matt]

Tried it and it worked. LS3 car.

[f5journal]

Originally Posted by brianko

Sure they will, if you ask nicely! I don't know about other tuners, but I don't subscribe to the "copy the high octane over the low octane" table theory when I tune a vehicle. (I think one of the tuning books out there advocates this.) The reason why it's a bad idea? The ECM interpolates between the high and low spark tables based upon knock sensor data. Copying the high data over the low data leaves no room for the ECM to interpolate a lower timing value, so the ECM is always pulling timing in response to KS events in the event of low octane fuel. Ideally, the ECM will "back off" of the highest spark value for a given engine load/RPM to compensate for KS events, then refer to the interpolated values for the remainder of the tank until you refuel.

Personally, if I'm tuning any GM that supports dual octane tables, I tune based upon the octane range the customer will be running. An 87/91 dual octane tune will require fewer changes to the low octane table than, say, a 91/93 tune. But blindly copying the high table over the low table isn't doing the customer any favors.

Strangely, the "LS1"-style PCMs (2006 and before) had no problems with adjusting for octane: Fill up with more than 6 gallons of fuel, and the PCM reset itself to read from the high octane spark table, adjusting for knock events after startup. Works very reliably.

The E38 computer in our vehicles *should* operate the same way (otherwise, the ECM would never adjust for octane changes), but it doesn't appear to do so. Whether it's a quirk in the GM programming or a deliberate change remains to be seen, as I've not seen any GM engineers step forward with an explanation (and I doubt they will). I've done back-to-back pulls on my dyno and it does appear the ECM seems to "lock in" to the low octane table, requiring a fuse pull to reset to the high octane table. Maybe GM will fix this in a future calibration update.

Assuming everything you have said is correct....I really appreciate this explanation. I was having a hard time understanding the KS relationship to the octance tables and also the "learning" part of the ECM. This bridges that gap

[malloyevelyn110]

how did I miss this thread? Like it

[PQ]

Originally Posted by RayYork

I can't either but I have read a few times here that you have to disconnect the battery on the LS3; not just pull the fuses.

I'm still unclear where that started and why. I'll have to ask Mike. But it can't really hurt anything. Just have to reset your radio setting and maybe re-index your windows.

Originally Posted by f5journal

I've done the pull 3 or 4 times now on my LS3. Each time it "seems" to be noticably better. However, it is always in the morning when cool and then later in the day I decide it did nothing

So as PQ suggested, I did some 0-60mph runs

All were right at 7 seconds +- 2 tenths. BUT, I forgot to turn off the A/C...and it was 98 degrees. None of the runs were perfect, but they were not "try agains". Slight missed shift on one, a little laydown bog on another and a pretty clean one with some tire spin.

I will try again on a cooler morning and see what I have. I think my car is going back to the low octane table soon after pulling the fuses and/or my knock sensors are detecting the weird noise in my engine or exhaust that I spoke to in another thread.

How are you timing it? 7 is freaking horrible.

Remember, too, that in the cooler morning air your car is gonna naturally run better. So it sounds normal.

Originally Posted by R8RUtz

I pulled my fuses for 5 hours, but once I put them backing I did not start the Car for another 15 hours. This definitely made a difference on my L99 motor.

I had put 87 octane in the car like be months ago.

Again all I can say is thanks, and wish I had read this sooner.

Awesome.

Originally Posted by Belle

So, I read this thread this morning. I pulled the fuses, waited for a few hours and re-installed them.

What a huge difference!

All this time, it felt like something was quite not right. So it was the low octane causing the lack of performance.

I've been using 91 (California) in my car from the get-go. The dealer that I bought the Camaro from must have put 87 and tricked the sensors.

Dang! I almost have 6K on my 2011 SS. I wish I knew about this fix 4 months ago.

Thanks for posting!

Good to hear.

Originally Posted by brianko

Sure they will, if you ask nicely! I don't know about other tuners, but I don't subscribe to the "copy the high octane over the low octane" table theory when I tune a vehicle. (I think one of the tuning books out there advocates this.) The reason why it's a bad idea? The ECM interpolates between the high and low spark tables based upon knock sensor data. Copying the high data over the low data leaves no room for the ECM to interpolate a lower timing value, so the ECM is always pulling timing in response to KS events in the event of low octane fuel. Ideally, the ECM will "back off" of the highest spark value for a given engine load/RPM to compensate for KS events, then refer to the interpolated values for the remainder of the tank until you refuel.

Personally, if I'm tuning any GM that supports dual octane tables, I tune based upon the octane range the customer will be running. An 87/91 dual octane tune will require fewer changes to the low octane table than, say, a 91/93 tune. But blindly copying the high table over the low table isn't doing the customer any favors.

Strangely, the "LS1"-style PCMs (2006 and before) had no problems with adjusting for octane: Fill up with more than 6 gallons of fuel, and the PCM reset itself to read from the high octane spark table, adjusting for knock events after startup. Works very reliably.

The E38 computer in our vehicles *should* operate the same way (otherwise, the ECM would never adjust for octane changes), but it doesn't appear to do so. Whether it's a quirk in the GM programming or a deliberate change remains to be seen, as I've not seen any GM engineers step forward with an explanation (and I doubt they will). I've done back-to-back pulls on my dyno and it does appear the ECM seems to "lock in" to the low octane table, requiring a fuse pull to reset to the high octane table. Maybe GM will fix this in a future calibration update.

I could possibly be just repeating the 'Copy the upper table onto the lower table' thing as I heard it. Might have been the easiest way for my tuners to say it, knowing I would not really understand it if they tried to be specific to me.

Thank you for your input. Sounds like you know your stuff. And another confirmation of the fuse pulls benefit.

Do you think that most tuners will understand the need to address this? Or is it plausible that there are people needing to pull the fuses even after a tune should they get low octane in it?

Originally Posted by ss/rs-matt

Tried it and it worked. LS3 car.

Thank you for posting. First post too. Awesome. Enjoy the car.

Originally Posted by f5journal

Assuming everything you have said is correct....I really appreciate this explanation. I was having a hard time understanding the KS relationship to the octance tables and also the "learning" part of the ECM. This bridges that gap

[f5journal]

Originally Posted by PQ

How are you timing it? 7 is freaking horrible.

Remember, too, that in the cooler morning air your car is gonna naturally run better. So it sounds normal.

I had a passenger too...she was using the iPhone stopwatch. Four days off starting now, so I will do some morning runs and report back. 7 seconds.. horrible....that's my fr.ckin point of all my posts and threads.....and now somebody posts that the no catch can deal can pull timing...and another posts the KS retard tables have been found screwed up on brand new untouched cars.........go figure....no, I'm figuring that I'll eventually figure this out. Dealer say "normal" Thanks PQ