How does PCM decide to switch between timing tables?
Thread Starter
TECH Enthusiast
iTrader: (1)
Joined: Nov 2004
Posts: 698
Likes: 0
From: Ontario, Canada
How does PCM decide to switch between timing tables? I am new to LS-1s but I have a lot of GM OBD-1 tuning experience.
I think I have read that the LS-1 has two timing tables to cope with KR due to octane changes. What triggers the change back and forth? I just bought my first LS-1 in a 2001 SS. The dealer had filled it with 87 octane. After it ran down I used 91 octane and nothing changed until the next time I used the car and it suddenly seemed to find a bunch more power.
Does it jump back and forth? How much knock is needed to switch down to the lower table? What makes it decide to go back up to the higher table? Once its on the lower table does it make fueling changes as well?
Lots of questions, feel free to point me to a link, I looked around but didn't see the answer.
TIA.
I think I have read that the LS-1 has two timing tables to cope with KR due to octane changes. What triggers the change back and forth? I just bought my first LS-1 in a 2001 SS. The dealer had filled it with 87 octane. After it ran down I used 91 octane and nothing changed until the next time I used the car and it suddenly seemed to find a bunch more power.
Does it jump back and forth? How much knock is needed to switch down to the lower table? What makes it decide to go back up to the higher table? Once its on the lower table does it make fueling changes as well?
Lots of questions, feel free to point me to a link, I looked around but didn't see the answer.
TIA.
TECH Senior Member
Joined: Nov 2001
Posts: 7,036
Likes: 1
From: Lake Zurich, IL
This i'm not 100% confident on... but I think is approximate?
First... if the PCM detects an issue w/the MAF it will default to low octane (hence why you need to copy high octane to low octane for SD tunes)
Now as for how it decides which table to use... I don't think it's cut or dry... use high or use low... I think the PCM learns based on driving... and kinda goes between the two, working up to the high octane only ... sustained periods of knock retard will bring it back to the low octane side
First... if the PCM detects an issue w/the MAF it will default to low octane (hence why you need to copy high octane to low octane for SD tunes)
Now as for how it decides which table to use... I don't think it's cut or dry... use high or use low... I think the PCM learns based on driving... and kinda goes between the two, working up to the high octane only ... sustained periods of knock retard will bring it back to the low octane side
TECH Addict
Joined: Jul 2002
Posts: 2,261
Likes: 0
Here's a link to the info ->http://www.efilive.com/forum/viewtopic.php?t=282 . Hope this helps some.
There is a Spark adaptive pid that you can look at in your scanner that will tell you the percentage of the high octane table and the low octane table being used. 100% means it is on the HO table any thing less than that the pcm blends between both tables
High/Low Octane Tables, the real story....
Originally Posted by GMPX
Hi all,
There appears to be alot of myths and confusion about the High and Low Octane tables in the LS1 PCM.
Well, hold onto your hats, we here at EFILive have been torturing our poor LS1's with junk fuel getting to the bottom of what really happens...
The PCM will ALWAYS try to run with the High Octane Table values, however if there is a MAF or Knock DTC set, it defaults to the Low Octane Table only.
But with a vehicle that has neither of those faults set it actually does a 'blend' of the two tables, it does not totally switch between one or the other.
In an upcoming release of EFILive there will be a new PID that will show you what percentage of the High Octane table values are being used (I'll refer to it as the Octane Multiplier).
Say for example the High Octane table has a value of 20 degrees, the same load point on the Low octane table has 10 degrees, and your octane multiplier is set at 50%, the final timing value would be 15degrees, if the octane multiplier is set to 75% it would result in 17.5 degrees, etc.
So what changes the Octane Multiplier value?, I have personally logged this on my car so I have seen it first hand. Basically any sustained amount of knock above about 2 or 3 degrees causes the Octane Multiplier to head towards 0%. It is a constantly changing value, it does NOT get reset to 100% when you fill up with fuel, the only thing that will bring it back to 100% and keep it there is minimal knock activity.
This has been tested on my own 2000 Commodore and emarkay's Camaro.
The PID will be supported for most LS1 powered cars/trucks.
On that note, if anybody has a BIN file or LS1 Edit file from a 2003 & 2004 Truck and 2004 C5, please PM me.
Phew, my fingers hurt after typing this........
There appears to be alot of myths and confusion about the High and Low Octane tables in the LS1 PCM.
Well, hold onto your hats, we here at EFILive have been torturing our poor LS1's with junk fuel getting to the bottom of what really happens...
The PCM will ALWAYS try to run with the High Octane Table values, however if there is a MAF or Knock DTC set, it defaults to the Low Octane Table only.
But with a vehicle that has neither of those faults set it actually does a 'blend' of the two tables, it does not totally switch between one or the other.
In an upcoming release of EFILive there will be a new PID that will show you what percentage of the High Octane table values are being used (I'll refer to it as the Octane Multiplier).
Say for example the High Octane table has a value of 20 degrees, the same load point on the Low octane table has 10 degrees, and your octane multiplier is set at 50%, the final timing value would be 15degrees, if the octane multiplier is set to 75% it would result in 17.5 degrees, etc.
So what changes the Octane Multiplier value?, I have personally logged this on my car so I have seen it first hand. Basically any sustained amount of knock above about 2 or 3 degrees causes the Octane Multiplier to head towards 0%. It is a constantly changing value, it does NOT get reset to 100% when you fill up with fuel, the only thing that will bring it back to 100% and keep it there is minimal knock activity.
This has been tested on my own 2000 Commodore and emarkay's Camaro.
The PID will be supported for most LS1 powered cars/trucks.
On that note, if anybody has a BIN file or LS1 Edit file from a 2003 & 2004 Truck and 2004 C5, please PM me.
Phew, my fingers hurt after typing this........
Last edited by HumpinSS; Nov 19, 2004 at 12:29 PM.
Thread Starter
TECH Enthusiast
iTrader: (1)
Joined: Nov 2004
Posts: 698
Likes: 0
From: Ontario, Canada
Thanks for the links, it appears lots of people wonder the same things I do. The first link worked and was a good thread. I seem to need a log-in for the second link to work.
Trending Topics
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo Thread Starter
TECH Enthusiast
iTrader: (1)
Joined: Nov 2004
Posts: 698
Likes: 0
From: Ontario, Canada
Presumably there is a quick value for pulling timing and a somewhat slower one for adding it back. Does anyone know how quickly it might add timing back in?
If you had a poorly shaped timing curve then the value of the multiplier would always be different depending on where you are in the tables. Does anyone know if the multiplier is actually series of values for different parts of the table or a single value? For example what if there was a single huge value in the upper table that always caused KR then is the multiplier driven downwards for every other part of the table too?
If you had a poorly shaped timing curve then the value of the multiplier would always be different depending on where you are in the tables. Does anyone know if the multiplier is actually series of values for different parts of the table or a single value? For example what if there was a single huge value in the upper table that always caused KR then is the multiplier driven downwards for every other part of the table too?
FormerVendor
Joined: Jan 2003
Posts: 525
Likes: 0
From: Melbourne, Australia
Originally Posted by BJM
Presumably there is a quick value for pulling timing and a somewhat slower one for adding it back. Does anyone know how quickly it might add timing back in?
If you had a poorly shaped timing curve then the value of the multiplier would always be different depending on where you are in the tables. Does anyone know if the multiplier is actually series of values for different parts of the table or a single value? For example what if there was a single huge value in the upper table that always caused KR then is the multiplier driven downwards for every other part of the table too?
If you had a poorly shaped timing curve then the value of the multiplier would always be different depending on where you are in the tables. Does anyone know if the multiplier is actually series of values for different parts of the table or a single value? For example what if there was a single huge value in the upper table that always caused KR then is the multiplier driven downwards for every other part of the table too?
