BLMs say rich, but WBO2 and NBO2 and surging all say lean - what gives?

[steveo]

there's also the argument that if you're going to run closed loop, you are never going to achieve the wideband AFR, all you'd be doing is making the BLM system work harder and harder to achieve an erroneous goal, so tuning to the trims would make more sense.. even if the AFR isn't great, at least it's consistent.

in other words i would tune to minimize trimming or abandon closed loop and tune OL with your wideband.

as far as PE goes, either method would yeild a reasonably accurate base fueling shape upon which power enrichment can be tuned properly to the wideband target anyway

[SkinnyG]

...so tuning to the trims would make more sense.. even if the AFR isn't great, at least it's consistent.

in other words i would tune to minimize trimming or abandon closed loop and tune OL with your wideband.

Am I understanding you correctly in that I tune so the computer/BLM is happy with whatever the end result it?

Could I just change the listed "stoich" to, say, 14:1, and the computer will stop trying to pull as much fuel out?

Or could I change the O2 Voltage Thresholds to higher switching points?

Just trying to wrap my head around all this.

Thank you all so much for your help!

[myburb]

I am not trying to be a smart ass but I don’t understand. Above there was a line in the post.

Even at idle and cruise the WB is around 14.7, but the ECU keeps pulling fuel. I set the BLM limit to 120, becase it would go 108 and run super lean.

Which is it, 14.7 or lean? It can’t be both. If the WB stays at 14.7 the ecm is doing what it has been ask no matter the blm say. It would only look like the ve table wasn’t very good.

[SkinnyG]

Ah, yes, that is unclear. My bad.

I can fatten the VE table until I get 14.7, but the BLMs see "rich" and pull fuel. If I set the VE to what the BLMs want (I lean out the VE), the BLMs still see rich and pull still more fuel to the point of surging and lean misfire. The engine just doesn't want to run where the BLMs want to take it. The ECU wants it leaner, but the engine isn't liking it. Idle, cruise, doesn't matter, the ECU wants leaner. When I look at O2 Averages in the History Table, the -average- voltage is already reading lean where the ECU want to pull still more fuel. The voltages are making sense to what the engine is doing - when it "feels" and "acts" lean, the O2 is telling me "it's lean" and the BLMs are saying "it's rich; pull fuel."

I've limited how far the BLMs can go (120 instead of 108), which has (for the most part) kept me out of lean surging (usually 14.7 at that point), but the BLMS will go right down to 120 trying to pull more fuel.

I'm having a thought that the ECU might be seeing a high IAT sensor and mathematically pulls fuel, despite the existing VE and O2 saying "we're good." Just a thought....

Does that make more sense??

[SkinnyG]

I guess I should clarify: this wasn't a "known good" setup to start with. The factory tune "worked" (more or less) with the unmolested LO3 305 V8, but I've put a very different engine in and I'm sorting it out and trying to make it work.

[SkinnyG]

Humble pie.

I max'd the Open Loop temperature, and set min and max BLM to 128, and went for a drive. OMG. Rich. Ok. So I will do a bunch of datalogging and mapping and get back to you all.

[SkinnyG]

Mind you, it did throw a High-MAP, Rich-O2, and EST codes. I'll check those out first. Maybe make sure the chip was fully seated....

[steveo]

Am I understanding you correctly in that I tune so the computer/BLM is happy with whatever the end result it?

Could I just change the listed "stoich" to, say, 14:1, and the computer will stop trying to pull as much fuel out?

Or could I change the O2 Voltage Thresholds to higher switching points?

Just trying to wrap my head around all this.

Thank you all so much for your help!

nope, closed loop is only capable of targeting what it percieves to be stoich, thats just how a narrow band trim system works. altering o2 voltage targets might get you +/- 0.1 afr or something

[SkinnyG]

Just looking at temperature multipliers. These don't really make sense to me.

IAT-ECT-Multipliers.JPG

On one hand, the coolant multiplier at 108°C should be giving me 3% -more- BPW. On the other hand, the IAT at 38 & 50°C (what I'm currently seeing) isn't changing the BPW at all yet. Still, closed loop should still be trying to maintain Stoich, right?

I -do- recall the stock 305 ran really strong for the first 3-5 minutes of driving, and then as it warmed up it became less and less exciting to drive. I never tested or scanned it before the engine died, though.

[dave w]

Screen shot below showing $OD closed loop tuning AFR averages with WBO2 data logs.

BLM averages below 128 indicate rich / BLM averages above 128 indicate lean. AFR averages below 14.7 indicate rich / AFR averages above 14.7 indicate lean.

Adjusting the $OD VE Tables rich or lean using WBO2 data, will have the same corresponding result (lower or higher AFR averages). Seemingly, adjusting $OD VE Table rich or lean will have the same corresponding results (lower or higher BLM averages).

I don't know if other definitions (like $4D) will have the same corresponding closed loop results with VE Table adjustments like $OD?

Some thoughts of some $OD WBO2 tuning I did:

"it's so cool and fun to drive the Blazer now. I like how smooth it runs. No hiccups, no stumbles, no knocking, runs great cold, hot, uphill, downhill, doesn't matter what I do to the pedal it just smoothly handles the inputs. I like how the torque converter locks up. I like how you tuned it to run more in the torque range. Shifts are right where they should be for this motor. There's nothing more I can ask for in a tune. I am so pleased to have stumbled across you. I would never be able to learn how to tune as you do. Thanks very much again for your service."

WBO2 - The best tuning tool ever!

dave w