** ECM TRUNK FUSE PULL **

[IndeedSS1]

Originally Posted by hapisok

i don't see how it could hurt, would be the same thing as if they were blown and running diagnostics on it. but i think having those removed and rolling the ignition over would help reset everything (circuitry stuff) so as not worry about "did i let it sit long enough" for an unspecified period of time.

Since it isn't trying to down or uplaod a tune it may be okay. You ahve an HP Tuners, give it a go and let us know

I just got back from setting my HPT to do standalone datalogging with Knock Learn Factor as an additional PID. I like the standalone since it allows me to easily do and save multiple scans both on the way to work and on the return trip then download later in the evening. I also created a Histogram to show the KLF at differnet rpms and cylinder airmass.

Since I go through a tank of gas every 4 - 6 days this test should take long. I'm only on a half tank now so Wednesday morning it will be time for more. I'll add a half tank of 87 and do some scanning, when that runs out I'll go back to 93 scan and see if the KLF is able to change it's reference to the low octane table.

If the ECM isn't able to regain timing on it's own what steps do you think would be nice to see? Pull 5 and 20 and put them right back and scan. Pull
them both and wait overnight before scanning, Pull the one in the trunk alone and scan

This is my daily driver so keep that in mind before suggesting anything that may be a pain in neck... well the pain in the neck part may be because I'm old and cranky

[hapisok]

definitely, i'll be checking it here in a few weeks once im back home.

i'll also be doing these:
1. 5 & 20 fuse pull...immediate reinstall
2. 5 & 20 fuse pull...roll ignition over
3. 10 fuse pull
4. 5 & 20 fuse pull...leave out over night (around 8 hrs)

other than fuel selection, is there a way to force the use of the lower octane table?

[IndeedSS1]

Originally Posted by hapisok

definitely, i'll be checking it here in a few weeks once im back home.

i'll also be doing these:
1. 5 & 20 fuse pull...immediate reinstall
2. 5 & 20 fuse pull...roll ignition over
3. 10 fuse pull
4. 5 & 20 fuse pull...leave out over night (around 8 hrs)

other than fuel selection, is there a way to force the use of the lower octane table?

If this works then the Fuel Trims should go back to zero as well, for those without Knock Lear Factor as a PID.

Your question is a good one about forcing the ECM to use the lower table. It would be interesting to know what parameters are being used to determine that the knock occuring is because of low octane. Remember it uses both tables, it is just how much each is referenced. Which begs the question, when does this get stuck on the low octane table and not able to start referencing the high again? When it hits 100% or what I'll assume for now is 1.00? I've been running 93 octane for 43k miles and my scans showed all hit cells as 0.00 KLF with no KR.

How long did the TSB say to leave fuse 5 and 20 pulled? Edit. Just looked and if I read it right, the TSB was only for automatics and the fuses were 13 and 20. Where did fuse 5 come in? I'm assuming someone assumed since the fuse diagram said ECM on #5 it should be pulled too?

[hapisok]

i wonder if its possible to force it into low octane table mode by pulling just one of the fuses...which one though, im not sure. need some schematics...

[IndeedSS1]

Originally Posted by hapisok

i wonder if its possible to force it into low octane table mode by pulling just one of the fuses...which one though, im not sure. need some schematics...

I'm pretty sure that isn't how it works. And the fuse(s) are only a default reset, like what you can do with the scanner and Long Term Fuel Trims.

[hapisok]

gotcha...yeah, thats not cool. do you know if the circuit level/board level schematics are available for the ECM? just to get a better understanding of how the different signals are tied together.

[skar]

My tuner said (I think)Fuse pull trick not necessary with a custom tune.
Also said never run less then 93 octane.

[IndeedSS1]

Originally Posted by skar

My tuner said (I think)Fuse pull trick not necessary with a custom tune.
Also said never run less then 93 octane.

That depends on the tuner. A good tuner will find out what you do with your car. If it is a daily driver then slighly bumping the low table may be okay, but I would never use a tuner that copies the high to the low. It's not best practices. Plus if you run high octane all of the time, it may only slightly reference the low but not for long.

[IndeedSS1]

Originally Posted by hapisok

gotcha...yeah, thats not cool. do you know if the circuit level/board level schematics are available for the ECM? just to get a better understanding of how the different signals are tied together.

I'm not sure if the schematics are made available for the ECM logic circuits, even in the shop service manuals, as those aren't repaired at the dealership level.
I really want the Helm manuals, but don't want to spend the money. I do have them for my Impala SS but that is a different platform.

[hapisok]

true, with a custom tune it isn't necessary. but we're trying to figure out the exact requirements/conditions of the reset for those who are un-tuned. i'll be switching my tune back to stock once i start going through the process.

they are designed to run on 87, hence the lower octane fuel table. but if you bought it for performance, your hurting yourself by running anything lower than 93. especially when it is known that these ECU's do not re-calibrate themselves to the high octane table which gives max performance when your putting 93 octane in it. essentially your not getting what you paid for. so if you put 93 in...pull the fuses and never put anything less than 93 back in it.

[hapisok]

Originally Posted by IndeedSS1

I'm not sure if the schematics are made available for the ECM logic circuits, even in the shop service manuals, as those aren't repaired at the dealership level.
I really want the Helm manuals, but don't want to spend the money. I do have them for my Impala SS but that is a different platform.

yeah, and alldata doesn't have anything that detailed either. thanks for posting though. guess it'll be trial and error

[Sharkss]

couldnt i just pull 5 and 20 and disconnect the battery? whats the point of the fuse in the trunk being pulled? i thought disconnecting battery does the same thing. am i wrong?

[IndeedSS1]

This is my three tables that I'll be looking at when doing my comparison. 43,7xx miles, always 93 octane and usually at the Shell around the corner from me.

[km9v]