BLM/INT question

[Fast355]

VE Fixer Spreadsheet Thread: http://www.gearhead-efi.com/Fuel-Inj...r-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)

BLM - Near Idle.jpg

BLM - Off Idle.jpg

Injector Duty Cycle.jpg

Near Idle.jpg

Off Idle.jpg

PE Active.jpg

Spark Advance.JPG

[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.