BLM/INT question

[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