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

[Camar0wn3d]

Originally Posted by Verio

Well, let it sit for 1.5 hours, didn't notice any difference. Then again, wife was in the car with me... and she said it seemed faster. Either mine is operating as it should, or it needs to sit longer. Pulled em again for the rest of the night... we'll see in the mornin

If you're not seeing any improvement after pulling the fuses it's because your ECU was already using the high octane tables before the fuse pull...

[SSRS2010]

Originally Posted by tribone

Here's a pic guys.


Attachment 48807

YES WE DID IT AND IT WORKS.WHY TRY TO OR ABOUT IT JUST DO IT THAT HOW I LOOK AT IT SO SO IF IT WORKS OR NOT THATS HOW IT IS.WE LIKE IT SO THANKS FOR THE HEADS UP

[Verio]

Originally Posted by wh0rsep0wer

If you're not seeing any improvement after pulling the fuses it's because your ECU was already using the high octane tables before the fuse pull...

Yeah, I understand that. But... my point is, my dealer put 87 in the car, I know he did because he told me. There is an underlying issue here on why some cars ECU is not readjusting to the different octane levels as they change. I've only put 93 into it since I picked it up.

[Camar0wn3d]

Originally Posted by Blueclyde

Back to the issue of spark tables and "clearing" the ECM. Most current automotive controls systems employ what is called "Adaptive" control strategy. The primary purpose of this strategy is to allow the engine controller to learn and re-adjust as the engine/vehicle goes through its normal use/wear life cycle. This strategy is one of the ways that the auto companies insure their vehicles comply with the EPA & CARB emission useful life periods legislated for on-highway vehicles (no trivial task here). This is nothing really new. This has been around for a while. One point that I would like to make is that these systems general learn bi-directionally. Meaning, if an engine subsystem has a problem (like a plugged air filter), the system will adapt to that. Once a problem is corrected the system will adapt back. Yes, resetting adaptive parameters back to zero (or "clearing" the ECM) will generally speed that process up, but it will also occur on its own over the course of normal vehicle operation.

The adaptive corrections SHOULD occur. But in a large number of the L99's, it hasn't been occurring. I agree that pulling the fuses is kind of a "hack" but the only way to truly correct it is through a ECU update from GM which we have no control over. Pulling the fuse and getting it to work with minimal effort essentially takes the ECU to factory defaults...I don't see a problem with that, especially since you won't have to do it again as long as you keep premium gas in the tank.

Originally Posted by Blueclyde

With respect to spark calibration tables and "93 Octane Tables" and "87 Octane Tables" I would be very surprised to find more than one spark calibration table in the control strategy. Again, I am no expert on the GM controller but I would be surprised if there are multiple tables. Generally there is one spark table that is calibrated across the speed and load range using the recommended fuel. I would think in this case with this being a performance vehicle the base spark calibration was done with high octane fuel. This engine is equipped with a knock sensor that is calibrated to detect and report occurrences of spark knock back to the engine controller. "Generally" engine control strategies use this knock sensor input data to "derate" or pull back spark advance from the base spark table. Calibrations are created to pull back the appropriate amount of spark for the input signal received from the knock sensor. There are probably other sensor based spark derate systems employed in addition to knock. Parameters such as intake air temperature and engine coolant temperature probably also have spark derates associated with them. If this is in fact the case, then none of this makes any sense, unless there are also other fueling corrections being made when the spark is being pulled out.

There ARE two tables (See screenshots below). There is spark derating that occurs in real time to correct for knock in certain cells WITHOUT the ECU giving up and going directly to the low octane table...This is known as knock retard - and is an "adaptive" set of values...but if it sees TOO much knock from the knock sensors it reverts to the low octane table.

Think of the high octane and low octane tables as a coarse adjustment to "get it in the ballpark" and the knock retard as a fine tuning adjustment...

These screenshots are from a 2002 Z28 factory default configuration...1st screenshot is the Spark Advance Menu, 2nd screenshot is the High Octane Table, and 3rd screenshot is the Low Octane Table. Notice the BIG differences between the two tables occur at WOT (the values at the bottom of each screenshot) THAT IS WHY THIS WORKS!!!

[BulletBob]

Just curious...
I live in CA where the hightest octane gas I've seen is 91. I realize some states have 93. So I'm wondering where the L99's ECU makes the determination on which of the two memory tables to use? If I use 91 octane, will the ECU boot the high power table?

[Camar0wn3d]

Originally Posted by Verio

Yeah, I understand that. But... my point is, my dealer put 87 in the car, I know he did because he told me. There is an underlying issue here on why some cars ECU is not readjusting to the different octane levels as they change. I've only put 93 into it since I picked it up.

Agreed ...like I said in my above post, this is a "hack" fix....It's up to GM to provide an update to REALLY solve the underlying problem.

[SSRS2010]

Originally Posted by wh0rsep0wer

The adaptive corrections SHOULD occur. But in a large number of the L99's, it hasn't been occurring. I agree that pulling the fuses is kind of a "hack" but the only way to truly correct it is through a ECU update from GM which we have no control over. Pulling the fuse and getting it to work with minimal effort essentially takes the ECU to factory defaults...I don't see a problem with that, especially since you won't have to do it again as long as you keep premium gas in the tank.



There ARE two tables (See screenshots below). There is spark derating that occurs in real time to correct for knock in certain cells WITHOUT the ECU giving up and going directly to the low octane table...This is known as knock retard - and is an "adaptive" set of values...but if it sees TOO much knock from the knock sensors it reverts to the low octane table.

Think of the high octane and low octane tables as a coarse adjustment to "get it in the ballpark" and the knock retard as a fine tuning adjustment...

These screenshots are from a 2002 Z28 factory default configuration...1st screenshot is the Spark Advance Menu, 2nd screenshot is the High Octane Table, and 3rd screenshot is the Low Octane Table. Notice the BIG differences between the two tables occur at WOT (the values at the bottom of each screenshot) THAT IS WHY THIS WORKS!!!

THANKS THATS HOW WE LOOK AT IT.GREAT JOB ON IT.

[jimpfromwv]

I pulled the fuses and left them out for 3 hours and the car does run better not a tremendous amount but it does run better. Idle quality is the biggest difference I noticed, it just feels smoother all over and the more I drove it the better it ran. In my opinion its well worth the time to do this.

[Camar0wn3d]

I have revised the screenshots for clarity...

[khislop007]

Originally Posted by SSOOCH

I'll try it on my LS3 tonight! With my pants on of course...

Originally Posted by FunkyELF

Awaiting your results.

[vdevine]

ECM issues with GM cars have been around for a while, normally just ECM fuses blowing because of a failing injector or something. This is a first I've heard about the octane problem but it does make sense. I've been having a rough idle so I'm curious to see if this temp fixes it. I believe you could also reset by removing the negative terminal ONLY from the battery. I'm going to disconnect my MAF sensor as well with this mod.

Best thread I've read so far.

[Blueclyde]

Originally Posted by wh0rsep0wer

I have revised the screenshots for clarity...

wh0rsep0wer:

I'm pretty amazed at the level of access you seem to have to automotive ECM calibration tables. I'm shocked the OEM's give out encryption keys to aftermarket software companies for this type of access. There must be some waivers signed for that. Do you actually have write access to those tables? If so it seems like an easy way to jack up an emissions calibration and subsequent catalyst life. I know most folks here have no concern about that but I could see a lot of so called "experts" out there with this type of tool really jacking things up.

So I can see from what you have shown, at least on the 2002 Z28, there are two cal tables. I guess my point revolves around the strategy code. I understand how you say it works in the presence of knock but why doesn't it revert after a key cycle? It would be really good to hear from somebody "in the know" from GM on this. No offense meant to you at all on this. You seem to know your stuff. Great info.

[Camar0wn3d]

Originally Posted by Blueclyde

wh0rsep0wer:

I'm pretty amazed at the level of access you seem to have to automotive ECM calibration tables. I'm shocked the OEM's give out encryption keys to aftermarket software companies for this type of access. There must be some waivers signed for that. Do you actually have write access to those tables? If so it seems like an easy way to jack up an emissions calibration and subsequent catalyst life. I know most folks here have no concern about that but I could see a lot of so called "experts" out there with this type of tool really jacking things up.

So I can see from what you have shown, at least on the 2002 Z28, there are two cal tables. I guess my point revolves around the strategy code. I understand how you say it works in the presence of knock but why doesn't it revert after a key cycle? It would be really good to hear from somebody "in the know" from GM on this. No offense meant to you at all on this. You seem to know your stuff. Great info.

Thanks...yes, with HPTuners you have write access to just about everything, including those tables. For example, the first step in creating a speed density tune is to copy the high octane tables into the low octane tables (which is why I was familiar with the concept of why the fuse pull works)...so it gets rid of your safety net....and you BETTER not put low octane fuel afterwards.

You are also correct about the ability to "jack" things up...it is extremely easy to blow up your motor changing parameters this easily...THAT is why dealers have a good case for voiding warranties based on ECM flashes. This should ONLY be attempted by professionals. In my case, I'm not a professional tuner but I work with instrumentation and control systems in the nuclear industry. More importantly I know just enough about it to know how easy it is to screw stuff up, so I'm EXTREMELY cautious with my tuning.

It is entirely possible that the tables are supposed to revert after a key cycle...it makes complete sense to do it that way. I'm also curious to find out the true prognosis on why some of these ECU's aren't reverting...

[Kripp]

It looks like that puller can be used two ways (on either the length or width of the fuse) as it has claws on both ends of the tool. If the fuse has a lip on the upper edge of all 4 sides, that is.... I am just guessing here as I have not looked at nor have I pulled any fuses for a long time.... and those fuses look smaller than ones I have seen in my youth.