Can any one explain what CL and OL are.
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Can any one explain what CL and OL are.
OL = Open Loop fueling, where the PCM is not using O2 sensor inputs to determine fuel delivery rates as interpreted from fueling tables.
CL = Closed Loop fueling, where the PCM now accepts O2 sensor input to adjust fueling rates to maintain as close to stoich an AFR as possible.
...in a nutshell :)
To further the explanation...
OL will be any time the car is below the CL temperature threshold (cold start) and WOT.
CL is part of what makes the EPA happy. CL is the PCM constantly chasing tail to achieve a 14.7:1 AFR
OL utilizes B3605 any time you start the car. ECT and time dictate when it goes to CL. WOT(PE) utilizes B3618.
how can I force the car to be in Ol or Cl? and what are the advantages of both?
You can force the car into OL by setting the CL temperature enabler to it's maximum value (described in the AutoVE tutorial). You could force CL by setting all the respective CL enablers to the minimum values.
OL prevents the PCM from self correcting fuel calculations allowing you to derive an air mass flow model. It can also be helpful for big cams when dailing in drivability
I don't really see an advantage to forcing CL outside the factory settings. GM has done a good job of enabling CL as soon as possible to please the EPA's emmisions requirements. When the engine is cold or running WOT (either PE or OLFA) it requires more fuel for optimum performance.
When in CL, the PCM commands the stoichiometric AFR and uses O2 closed loop feedback to trim to that AFR;
When cold or at WOT (or when PE kicks in), the engine requires a richer AFR as TAQ said; the O2 sensors are only accurate very close to stoichiometric AFR; if the PCM wants a richer AFR, the O2 sensors won't be able to be used for closed loop feedback, so the PCM goes to OL (stops trimming to stoichiometric AFR) where it now looks up the commanded AFR in tables (the richer of OLFA (B3605/B3647) and PE (B3618) when PE has enabled).