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<TITLE>RE: WOT open loop/closed loop</TITLE>
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<P><FONT SIZE=2>Ron, </FONT>
<BR><FONT SIZE=2>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.)</FONT></P>
<P><FONT SIZE=2>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.)</FONT></P>
<P><FONT SIZE=2>The Max BLM is 160 (25% enrichment), Minimum is 108 (about 15% enleanment.)</FONT>
<BR><FONT SIZE=2>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.</FONT></P>
<P><FONT SIZE=2>Hope this makes sense,</FONT>
<BR><FONT SIZE=2>-Christian.</FONT>
</P>
<P><FONT SIZE=2>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.</FONT></P>
<BR>
<P><FONT SIZE=2>At 03:27 PM 9/24/01 -0400, you wrote:</FONT>
<BR><FONT SIZE=2>>> From: Ron Schroeder [<A HREF="mailto:rjs@bnl.gov">mailto:rjs@bnl.gov</A>]</FONT>
<BR><FONT SIZE=2>>> Subject: RE: WOT open loop/closed loop</FONT>
<BR><FONT SIZE=2>>> </FONT>
<BR><FONT SIZE=2>>> So with a WB O2 sensor, you could go closed loop.</FONT>
<BR><FONT SIZE=2>>></FONT>
<BR><FONT SIZE=2>></FONT>
<BR><FONT SIZE=2>>Well, it'd require some pretty significant code changes, I think.</FONT>
</P>
<P><FONT SIZE=2>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)</FONT></P>
<P><FONT SIZE=2>>That, and</FONT>
<BR><FONT SIZE=2>>the consequences of some sort of hardware failure at WOT would be a bit </FONT>
<BR><FONT SIZE=2>>severe.</FONT>
</P>
<P><FONT SIZE=2>Hopefully the BLM will prevent a correction of more than +/-20%?????</FONT>
<BR><FONT SIZE=2> </FONT>
<BR><FONT SIZE=2>>> I was going to ask about the BLMs in WOT. So maybe the ECM</FONT>
<BR><FONT SIZE=2>>> looks at the O2</FONT>
<BR><FONT SIZE=2>>> only to be a fail safe to prevent running leaner than 14.7:1.</FONT>
<BR><FONT SIZE=2>>> </FONT>
<BR><FONT SIZE=2>></FONT>
<BR><FONT SIZE=2>>The LT1 PCM isn't looking at the O2 sensor at all. What it's doing is </FONT>
<BR><FONT SIZE=2>>using the closed-loop BLMs from the last cell used before </FONT>
<BR><FONT SIZE=2>>power-enrichment mode is entered. But, it only uses those BLMs if </FONT>
<BR><FONT SIZE=2>>they're above 128. If the last closed-loop BLM was under 128, the PCM </FONT>
<BR><FONT SIZE=2>>automatically uses a BLM of 128 to ensure that it always errs on the </FONT>
<BR><FONT SIZE=2>>rich side (this way, some freak event that cause a false low BLM at </FONT>
<BR><FONT SIZE=2>>part-throttle won't cause lean operation at WOT).</FONT>
</P>
<P><FONT SIZE=2>Makes sense.</FONT>
</P>
<P><FONT SIZE=2>>> So since part throttle uses BLMs (and the integrator), tuning</FONT>
<BR><FONT SIZE=2>>> in that part</FONT>
<BR><FONT SIZE=2>>> of the maps will do very little unless the BLM values are WAY out but</FONT>
<BR><FONT SIZE=2>>> tuning the WOT part of the maps could bring out lots of </FONT>
<BR><FONT SIZE=2>>> improvement. Or am I off base?</FONT>
<BR><FONT SIZE=2>></FONT>
<BR><FONT SIZE=2>>For some reason, the LT1 PCM uses a VE table, despite the fact that it </FONT>
<BR><FONT SIZE=2>>has a MAF sensor. Tuning the VE tables to keep closed-loop BLMs at or </FONT>
<BR><FONT SIZE=2>>very near to 128 seems very important with this motor. If the </FONT>
<BR><FONT SIZE=2>>closed-loop BLMs start to creep away from 128, WOT fueling becomes </FONT>
<BR><FONT SIZE=2>>difficult to predict (see my above explaination), and the part-throttle </FONT>
<BR><FONT SIZE=2>>drivibility and fuel economy also seems to suffer.</FONT>
</P>
<P><FONT SIZE=2>I can see part throttle drivability and throttle response but economy doesn't make sense.</FONT>
</P>
<BR>
<P><FONT SIZE=2>Ron Schroeder</FONT>
<BR><FONT SIZE=2>WD8CDH</FONT>
<BR><FONT SIZE=2>E. E. S.</FONT>
<BR><FONT SIZE=2>wd8cdh@bnl.gov</FONT>
<BR><FONT SIZE=2>rjs@bnl.gov</FONT>
<BR><FONT SIZE=2>ron@112motors.com</FONT>
<BR><FONT SIZE=2>631 344-4561 Day</FONT>
<BR><FONT SIZE=2>631 286-5677 Nite</FONT>
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