BLMs not responding to VE change

[FUN-9C1]

I have a "new" (to me) OBD1 Impala SS. The PO had installed headers and K&N intake, but no programming. First thing I tried was, since my BLMs were consistently about 142 ish, I multiplied the entire VE table by 1.11.

I was surprised to see that my BLMs are still consistently in the low 140s. What gives?

[lionelhutz]

Car has a MAF sensor?

[FUN-9C1]

Yes.

[steveo]

with a maf, you're metering with the maf, not speed density, your ve table is ignored. you need to scale the maf table instead.

something else might be going on too, in my experience tuning LT1s, usually a cold air intake and headers don't kick your BLMs up like that. just make sure you aren't tuning around a problem (vacuum leak or whatever)

[FUN-9C1]

Ahh, OK, thanks for the reply. One thing I have trouble wrapping my head around- If the O2 sensors are constantly adjusting for a 14.7:1 AFR, isn't it going to just "adjust out" any changes I make? Or to put it another way, why is tuning necessary if it's always adjusting for the ideal 14.7 (not counting WOT stuff)? Like say with headers, shouldn't the PCM adjust the fuel to get 14.7? Yes, the BLMs will not be 128, but who cares, as long as the AFR is 14.7? That may be oversimplifying but you get my question?

[lionelhutz]

Well, what about the areas where it isn't running closed loop and self correcting like WOT? If you get it as close to correct as possible then the fueling will be more accurate during these times. There is a WOT BLM locker that locks out the BLM so it relies on your tuning. This avoids the PCM using a BLM value that throws your tuned AFR off.

Another thing is that the BLM cells are rather large and each one cover a large portion of the operating range. The VE table has way more cells then the BLM table. 27x17 cells vs 4x4 cells.