WOT open loop/closed loop

[cmillard at crutchfield.com]

Ron, 
Eric has done a good job of explaining a lot of the logic as well know it,
we're still waiting on the flowchart from GM though (hehe.)

The GM 4 wire O2 sensors are designed to "switch" at 450 mv = 14.7:1 AFR. If
we can make a hardware device that will offset the WB O2 sensor voltage to
that, then I can't see why it shouldn't work, the factory doesn't care or
know if 500 mv = 13.7:1 or 11.5:1, it only counts how many times it stays
above(or below) 450mv.  I would definitely be a happy puppy (and a couple
hundred other people.)

The Max BLM is 160 (25% enrichment), Minimum is 108 (about 15% enleanment.)
Beyond that point the engine uses the OpenLoopAFR Fueling table, which I
believe is constantly being compared to in PowerEnrichment mode as well.
This explains the beloved BLM "cell 15" vs "cell 18" events that everyone
loves to see. I've stared at the DIS for night after night trying to discern
that one with no luck.

Hope this makes sense,
-Christian.

P.s. The factory BLM boundaries are pretty worthless once a perfromance cam
is installed, I'll be shamelessly requesting someone to share the BLM
boundary addresses for a 16188051 (EE) pcm if anyone knows them.


At 03:27 PM 9/24/01 -0400, you wrote:
>> From: Ron Schroeder [mailto:rjs at bnl.gov]
>> Subject: RE: WOT open loop/closed loop
>> 
>> So with a WB O2 sensor, you could go closed loop.
>>
>
>Well, it'd require some pretty significant code changes, I think.

Possably a hardware analog offset on the scaled O2 sensor reading triggered
by a WOT switch before feeding the ECM.  (Instrumentation is my specialty, I
do scaling and offsets every day)

>That, and
>the consequences of some sort of hardware failure at WOT would be a bit 
>severe.

Hopefully the BLM will prevent a correction of more than +/-20%?????
 
>> I was going to ask about the BLMs in WOT.  So maybe the ECM
>> looks at the O2
>> only to be a fail safe to prevent running leaner than 14.7:1.
>> 
>
>The LT1 PCM isn't looking at the O2 sensor at all.  What it's doing is 
>using the closed-loop BLMs from the last cell used before 
>power-enrichment mode is entered.  But, it only uses those BLMs if 
>they're above 128.  If the last closed-loop BLM was under 128, the PCM 
>automatically uses a BLM of 128 to ensure that it always errs on the 
>rich side (this way, some freak event that cause a false low BLM at 
>part-throttle won't cause lean operation at WOT).

Makes sense.

>> So since part throttle uses BLMs (and the integrator), tuning
>> in that part
>> of the maps will do very little unless the BLM values are WAY out but
>> tuning the WOT part of the maps could bring out lots of 
>> improvement.  Or am I off base?
>
>For some reason, the LT1 PCM uses a VE table, despite the fact that it 
>has a MAF sensor.  Tuning the VE tables to keep closed-loop BLMs at or 
>very near to 128 seems very important with this motor.  If the 
>closed-loop BLMs start to creep away from 128, WOT fueling becomes 
>difficult to predict (see my above explaination), and the part-throttle 
>drivibility and fuel economy also seems to suffer.

I can see part throttle drivability and throttle response but economy
doesn't make sense.


Ron Schroeder
WD8CDH
E. E. S.
wd8cdh at bnl.gov
rjs at bnl.gov
ron at 112motors.com
631 344-4561 Day
631 286-5677 Nite
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