BLM/INT question

[Kitch]

I've just been looking at the logs from my new 383 after a 40 minute test run on the motorway.
I was holding a pretty consistent 60MPH and the BLM sat on 117 most of the time and it varied between 113-119, I would read that as richer than stoichiometric.
The INT was sitting around 125-130, if the BLM was 128 that would be great but it's not.

I assumed the Integrator would try and pull the BLM from around 117 up to around 128 but the INT seems happy holding the BLM around 117.

I'm obviously missing something here, any help explaining what it is would be appreciated.

[Terminal_Crazy]

Wrong way around

Presuming OLSD

The VE is rich so BLM is lower than 128 pulling fuel. The INT has settled hovering around 128 where it's happy.

If the INT gets to about +-5 the BLM should move in that direction & INT resets to target around 128 again.

VE Cell should be lowered by 116/128 around 10%. I'd only adjust it by around 3% or less as you'll overshoot.


Mitch

[Kitch]

Thanks for the reply.

I can't presume OLSD because I don't know what OLSD means! :)

Still trying to get my head around why "The INT has settled hovering around 128 where it's happy." Why is it happy with a BLM of 117 rather than 128?

So the INT only tries to move the BLM value if it goes above or below 128 by 5, that by itself makes sense. As above, not sure why it seems happy with the 117 BLM?

I had figured that it was about 8-10% Rich from the 117 BLM, thanks for the confirmation though.
Since that log I've reduced the VE table by 5%, I haven't had a chance to test it out yet.

Cheers,
Andrew

[Terminal_Crazy]

OL SD = Open Loop Speed Density.
Speed Density is NO MAF, just the VE Tables
You're running CL Closed Loop as you are using the CL feedback from the narrow bands.

IF You are running MAF, I think the VE Tables aren't used & you need to play with the MAF Tables


The integrator hovers around Stoich. PCM counts Cross counts of the Narrowbands going rich & lean.

If it's rich & the INT has moved down by around 5 counts The BLM lowers reducing fueling & the INT tries again.
With the BLM pulling fuel (8-10%) the integrator is hovering around stoich again so is happy.

Mitch

[Kitch]

Thanks again for the reply.

I had guessed SD might have represented speed density :)
No MAF just an old 7427 PCM.

Okay... so the Integrator tries to hover around Stoich!
That now makes more sense and explains why you said I had it the wrong way around.

If I'm understanding this the BLM at 117 is representing where the INT has already pulled it to, so that's why the INT is now in it's happy 128 place?

If you don't mind I now have another question, if the Integrator can move the BLM to operate the engine's EFI at Stoich what's the big advantage in altering the VE table so the BLM ends up close to 128?
I've altered VE tables many times to get it close to get the BLM to show 128 but never thought about the advantage in having it as close as possible to 128 vs letting the Integrator sort it out?

Cheers,
Andrew

[steveo]

block learn mode (blm) is in bigass blocks

it can adjust like 1/4 of the table at a time

it cant change the shape of the table

fine adjustments yeild better drivability overall

also some things dont take blm trims into account

open loop and wide open throttle often dont

blm and int are displayed poorly in almost all gm software you should see it as a percentage to know what's actually going on

[Kitch]

Thanks Steveo,

I think I'm happy with the BLM INT relationship now.

Most of your statements above sound familiar to me.
I'll need to do some more reading up about BLM and the main reason you'd want it to be close to 128.

While I'm getting dumb questions out of the way.
Presumably the PCM saves to memory the changes the INT has made to the BLM, so next time you start your vehicle they're still all there.
If you power-down the PCM or upload a changed .bin file will the BLM/INT learning process starts all over again?
The VE table is a constant that the PCM works with but can't physically change/edit?

Cheers,
Andrew

[dave w]

Sample of a BLM correction spreadsheet.

BLM correction formula = Current BLM / 128

Example shows rich BLM's

19156

[LeMarky Dissod]

Presumably the PCM saves to memory the changes the INT has made to the BLM, so next time you start your vehicle they're still all there.
If you power-down the PCM or upload a changed .bin file will the BLM/INT learning process starts all over again?Each pcm has limits to what it keeps from the previous engine run.
In other words, not ALL the changes; some, maybe most - depends on the pcm or what the .bin file allows.
Powering down the pcm or uploading a new .bin file is a fresh start.
The VE table is a constant that the PCM works with but can't physically change/edit?Exactly.

[dave w]

Sample of a BLM correction spreadsheet.

BLM correction formula = Current BLM / 128

Example shows rich BLM's

19156

VE Fixer Spreadsheet Thread: http://www.gearhead-efi.com/Fuel-Injection/showthread.php?342-E6-OE-OD-31-42-VE-Fixer-Spread-Sheet

[Fast355]

VE Fixer Spreadsheet Thread: http://www.gearhead-efi.com/Fuel-Injection/showthread.php?342-E6-OE-OD-31-42-VE-Fixer-Spread-Sheet

I target a BLM around 124 rather than 128, keep it a little rich and let the PCM and 02 sensor sort it out.

[Kitch]

Hi Fast,

Can I get a little more detail on why you like to keep it a little rich around 124, what's the main benefit you've found?

Cheers,
Andrew

[dave w]

Interesting data:

Same Chip with multiple data logs combined, approximately 140,000 data points.

Same Excel spreadsheet / Same "data crunching" formulas (MACRO's)

19159

19160

19161

19162

19163

19164

19165

[Fast355]

Hi Fast,

Can I get a little more detail on why you like to keep it a little rich around 124, what's the main benefit you've found?

Cheers,
Andrew

Hello Andrew,

I find two benifits. Generally speaking it prevents lean spots and the associated drivability quirks before the PCM can adjust the long term fuel trims. Second it prevents the PCM from adding additional fuel across the whole RPM range if you enter PE with the BLM higher than 128. If you go WOT at a BLM value of say 135, the PCM will add ~5% fuel everywhere.

[Kitch]

Hi Fast,

Thanks for the explanation, in future I'll look at keeping the BLM in the 124-128 range or I won't be so worried if it's a bit below 128.

Interesting thing I noticed today while logging, cruise BLM were pretty close to what I wanted but after I filled up the gas tank and they all went rich.
I've fitted a CCP solenoid to my RamJet intake and I'm guessing the CCP solenoid was pulling more than just vapours, I took it for a run out on the motorway to confirm and by the time I got back it looked to have settled down.
I think my 2001 Tahoe's PCM doesn't operate the CCP solenoid if the tank is full, I don't think my 7427 PCM is that clever.

Cheers,
Andrew

[MO LS Noobie]

Interesting thing I noticed today while logging, cruise BLM were pretty close to what I wanted but after I filled up the gas tank and they all went rich.
I've fitted a CCP solenoid to my RamJet intake and I'm guessing the CCP solenoid was pulling more than just vapours, I took it for a run out on the motorway to confirm and by the time I got back it looked to have settled down.

I think that you can safely ignore the data right after a refueling event. This is normal, provided your charcoal canister is functioning properly and you are not getting any raw gas into it, or topping off the fuel level after auto shut off of the gas nozzle. You can turn off the canister purge valve until 1200 RPM, this will disable it at idle and only allow it operate and higher airflows.

[badgta]

Here is some food for thought..

My computer says i have a BLM of 137 and INT of 140-135 which would scream "LEAN" or the computer adding fuel.. But the AEM UEGO W.B says she is (PERFECT) at 14.5-14.7:1 AFR!!!


Don't know why it is like that, i thought the 02 sensor was bad and installed a brand spanking new one just to be sure, and it read the same.. high 130's-140's for stioch! On mine anyways..

Only thing i can figure is maybe the cam causing the signal to be skewed due to overlap... LT4 Hotcam..

[MO LS Noobie]

This table looks different than the one I usually use, but it looks like you need to add about 10% fuel in this area. This is the reason for tuning, you have changed the engine that the computer was set up for, and you need to adjust the tune to match the new engine volumetric efficiency.

[badgta]

I'm not gonna add fuel to a perfect 14.7:1 stioch AFR No sense, The NB is off... I trust that WB a LOT more than that NB! That is a log on the EBL P4.. Hence the difference.

[steveo]

wait wait
so you see a blm of 140 in closed loop
but while that blm shows your wide band reads 14.7:1?
.... you do realize that means your ecm has achieved a stoichiometric mixture by adding a bunch of fuel, right?

[steveo]

and you do realize that if you add that missing fuel back
that won't make it richer
itll just make it trim less
.... right?

[MO LS Noobie]

wait wait
so you see a blm of 140 in closed loop
but while that blm shows your wide band reads 14.7:1?
.... you do realize that means your ecm has achieved a stoichiometric mixture by adding a bunch of fuel, right?

Exactly, it is doing its job. It just has to work harder to get to 14.7:1 if it has to add/subtract a lot of trim.

[Fast355]

I'm not gonna add fuel to a perfect 14.7:1 stioch AFR No sense, The NB is off... I trust that WB a LOT more than that NB! That is a log on the EBL P4.. Hence the difference.


You do not want the ECM having to add the extra fuel via closed loop. Fix your VE tables and get your BLMs in the 124-128 range. The engine will run more smoothly and responsive. The narrowband is not off, it is working as it is meant to work, adding fuel for a lean condition in the VE tables. All of your Open Loop fueling is currently based off a VE table that is wrong.

[badgta]

You know.. I never really thought of it that way...

Interesting indeed...


I try to stay away from Open Loop as much as possible... Just like CL operation personally... Just ordered a new Hellcat 525LPH fuel pump for it, and redone the Aermotive Compact EFI VAFPR the other day with a new diaphragm and made sure it was good and clean.. Been chasing a weird stall issue while in drive/reverse gear in idle only...

Once i get that in, i may try to dial it in more.. Not gonna chase my tail until mechanical is 99.9% certain... I am sure you would agree with that.....

[steveo]

I try to stay away from Open Loop as much as possible... Just like CL operation personally...

it isn't possible to stay away from open loop. your ECM likely runs open loop during many conditions including warm up, acceleration, deceleration, and heavy throttle. closed loop is acceptable fuel economy and emissions in steady state cruising only. that's what the factory uses it for and that's what you use it for whether you realize that or not. closed loop on these old things doesn't magically correct a bad VE table even if it does manage to find 14.7:1 once it's caught up long term trims. it trims in huge blocks so the shape of the VE table is not corrected by closed loop at all. having high trims means your fueling is incorrect, or something is wrong