How cranking determined?
Thread Starter
Teching In
Joined: Oct 2006
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How cranking determined? I notice overlap in the cranking and Primary VE tables. How is "cranking" determined? I assumed that RPM would generally be used to determine "cranking" but based on the VE table overlap, I imagime that there should be other criteria .
Any help would be great.
Any help would be great.
Thread Starter
Teching In
Joined: Oct 2006
Posts: 13
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I would like to understand how the cranking VE Table is used. I assume the PCM uses this table while cranking and I was wondering how the PCM would detect cranking. The Primary VE Table has overlapping RPM values with the cranking VE table and how would the PCM know which table to use?
I am tuning my setup and it would be nice to know how the PCM determines which of these overlapping tables to use at say 800 RPM ...
I am tuning my setup and it would be nice to know how the PCM determines which of these overlapping tables to use at say 800 RPM ...
The PCM uses the crank sensor and reluctor wheel rotation to determine actual cranking. There is some overlap between the two tables when cranking. The Cranking VE is very sensitive to adjustments and requires very little adjustments compared to the main VE table. Like I mentioned above, look at the Commanded Fuel When Cranking table. It commands the air/fuel ratio when cranking based on ECT and the number of times the reluctor wheel indicates 90 degrees of engine rotation. It's also very sensitive to adjustments.
Thread Starter
Teching In
Joined: Oct 2006
Posts: 13
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I understand that the PCM can measure the RPM and phase based on the crank and cam sensors but how does it choose a table. Assume the crank and cam sensors measure 800 RPM and the MAP reads 30. Is it "cranking" and therefore uses the Cranking VE Table (586) or is it "running" and therefore uses the Primary VE Table value (1215)? (The values are taken from my stock LS1 setup)
The values from the 2 tables are very different and it would be nice to know which one is being used and when.
It is not the conceptual understanding of the PCM function that confuses me but rather the usage of a particular table when there is RPM overlap.
Thanks for all of the help. Any new help is greatly appreciated.
The values from the 2 tables are very different and it would be nice to know which one is being used and when.
It is not the conceptual understanding of the PCM function that confuses me but rather the usage of a particular table when there is RPM overlap.
Thanks for all of the help. Any new help is greatly appreciated.
