WOT open loop/closed loop

[Ron Schroeder]

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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