daveb
May 9th, 2005, 02:48 PM
I am a little puzzled about how ltfts work, in particular when we are in open loop mode.
I understand how they operate in closed loop and I am happy with part throttle tuning.
When tuning for WOT the system is, of course, in open loop mode. I understand that the PCM uses the VE table to determine the fuel required, adjusts this by any PE enrichment value (and any other anciullary changes required, ie ECT tmp etc) to determine the fuel it delivers.
My question is this: Does the PCM only use the VE table to determine the fuel requirement? I have read this is the case, hence the need to get the VE tables correct using a WBO2 sensor etc.
If so why does the PCM read ltft values when in open loop. Does it use the VE table and increase/decrease the value based on the ltft value before using any PE enrichment? I thought while in open loop mode the system ignores the O2 sensors, so why do we get ltft numbers for cells which cannot be visited in closed loop mode?
I assume someone with access to the assembly code of the PCM internals (Ross) will know this.
I hope I am making sense here. Keen to know your thoughts.
I understand how they operate in closed loop and I am happy with part throttle tuning.
When tuning for WOT the system is, of course, in open loop mode. I understand that the PCM uses the VE table to determine the fuel required, adjusts this by any PE enrichment value (and any other anciullary changes required, ie ECT tmp etc) to determine the fuel it delivers.
My question is this: Does the PCM only use the VE table to determine the fuel requirement? I have read this is the case, hence the need to get the VE tables correct using a WBO2 sensor etc.
If so why does the PCM read ltft values when in open loop. Does it use the VE table and increase/decrease the value based on the ltft value before using any PE enrichment? I thought while in open loop mode the system ignores the O2 sensors, so why do we get ltft numbers for cells which cannot be visited in closed loop mode?
I assume someone with access to the assembly code of the PCM internals (Ross) will know this.
I hope I am making sense here. Keen to know your thoughts.