I'm obviously missing something fundamental. Last night, I was using the innovate wideband, with a fresh sensor and free-air calibration - the car would idle with AFR very near or on 14.7

Whats confusing to me is that the ECM (stock '6026 - my '8746 is getting some upgrades) was reporting 108 BLM.

The o2 sensor (one wire in shorty headers) was reading in the .7 range... I have not changed the narrow-band sensor recently.

I'm confused because the 108 is telling me the car is way rich, and but the wide-band says (at that moment) its dead on.

Now the wb is in the ypipe, so it sees both sides of the exhaust - one theory is that the tb's aren't balanced or the injectors aren't flow-matched...

Somehow the ECM was maintaining stoich for that moment, but yet it was reading 108 BLM....

I figure I'm missing something basic here - if anyone wants to provide me a clue, I'm ready to learn

 

No, 108 is showing you how much off the ve table is. The ecm will maintain 14.7 untill blms cannot compensate. So changing the ve tables will get you 128 blms but still keep you at 14.7. hope that helps

 

Ok - that's much closer to how BLMs were originally explained to me, but along the way, everyone seems to discuss BLM as more of a direct indicator of rich / lean so I'd begun to think of it as more of a direct indicator.

Thanks!

 

the ecm is "stuck" at 14.7 for normal driving.THe only way(in general) to run a different a/f IF the blms are maxed out. Right now I'm trying to figure out how to command any a/f ratio for part throttle/idle.


Good Luck on your tune!

 

So if my BLM is at 108 and I'm still getting knock retard, I should probably pull spark out?

 

NO!

 

Sorry. I'm still a bit new to doing my own chips. I guess I should go read the stickies again :\

 

If you didn't add spark then dont remove it(just yet). Start with getting your fuel correct THEN figure out the knock retard. There is a billion things that can cause knock counts. You might want to read up on that. It's common to get knock counts. Ckeck if the ecm is retarding the timing. Good Luck!

 

my advice is to lock the blm high and low at 128. and the integrator. Then look at the wideband and see what you get. Youll also want to disable all the trobule code associated with the o2 sensor to keep from pissing it off. After you do this the ECM will stop correcting the fuel trim and youll be able to see what the afr is. If you disable the CL operation on a 8D code ecm it will run on different tables

 

my opinion (and i'm not the most knowledgeable or most experienced on here by far),

i'd at least get the VE table somewhat close (into the 120's or low 130's) accross the board, before locking the int and blm, with a tune that far off you might run things way too rich or way too lean.

also. think of the blm as a correction factor. it is the correction applied to the VE table to hit (approximately) 14.7:1.

you can have 108 BLM and 150 BLM and still be at 14.7:1. in the first case, (108 BLM) it means that the VE tables are too rich at that MAP/RPM spot, and the computer is correcting by taking out fuel to hit 14.7:1. vice versa for 150 (it's adding fuel because the VE table is too lean).

another way to think of it (i don't know if my analogies are of any use to any one at all, but nobody has complained yet), is to think of the VE/fuel like a hot water heater. if the hot water heater thermostat is too high, then you have to turn the water faucet to the cold side to counteract the incorrect water heater thermostat in order to get luke warm water. on the flip side if the hot water heater is set too low, you have to turn the faucet almost full hot to get luke warm water. both ways you get luke warm water but the heater can have very different thermostat settings. you counteract with the faucet, kind of like the blm counteracts the VE table to get the right mixture as determined by the o2 sensor.