VE Correction Factor P01/P59
Posted: Wed Jun 22, 2022 8:54 am
Gents,
I have a tuning question, but to understand how or if to adjust I must first understand what the underlying code is doing.
I have a 496 big block running a P59 in speed density, uses an EFI COS based on OS ..618. Has large AFR heads and 244ish cam with a bunch of overlap. The VE table and everything else is tuned at operating temp as would be normal practice. What I realized though is starting cold and allowing the engine to warm up, the air mass model in the PCM is way off(high, so engine runs very rich) and tapers back to correct as the engine warms up. To fix this in a pinch, I'm taking out ~50% of the fuel at 40C and taper to 1EQ at operating temp. This works and keeps the engine from fouling out while warming up.
B3605, OLFA table, in lambda. This works, but I consider it a band aide to a larger problem. This whole tuning process has been overshadowed by what I consider large amounts of desired base airflow and startup airflow. My theory is that if the airmass model is wrong at less than operating temp conditions, and reporting higher than necessary airflow and therefore providing more than necessary fuel, that any sort of RAFPN tuning would be skewed at lower temps and give me the higher numbers. I'll mention, the engine starts fine hot.
For whatever reason, it appears this engine combo is much less efficient at lower coolant temps, so I started looking for a table to adjust the VE based on coolant temp. I found the VE correction factors in the ...604 XDF as well as in HPT. So I ported those tables over to EFI for the ...618 OS and am ready to try modifying them, but I'm realizing I don't understand how the table functions.
The description is that the VE Correction factors in the tables are used to initialize a value, which I figured is then updated. Without a MAF, running speed density I'm not sure how it can be updated? This is where I'm looking for some insight into the OS of the PCM to understand how the values from this table are used within the speed density dynamic air mass calc. Are the correction factors reloaded often from this table? or maybe only at startup? Are these corrections multiplied into the VE table, or divided?
Potentially I can log EQ error correction between commanded and actual and use that to 'tune' in this table for different coolant temperatures. At the least I figure I can set this whole table to 1.0, and set the min and max correction to 0.999 and 1.001 and at least make it one less modifier to get in the way.
If this table isn't what I need to modify then I guess I will stick to looking for a problem with the dynamic temperature calc. Potentially it is an issue with the IAT being mounted in the aluminum intake manifold and instantly heat soaking(single plane carb style intake)....but the IAT is believable as it's just a standard 14" airfilter that draws in underhood air.
Curious what you guys know about how these internal VE corrections are used, and how they are best adjusted for speed density tunes. From what I gather here I can make a plan for my next moves. Thanks!
I have a tuning question, but to understand how or if to adjust I must first understand what the underlying code is doing.
I have a 496 big block running a P59 in speed density, uses an EFI COS based on OS ..618. Has large AFR heads and 244ish cam with a bunch of overlap. The VE table and everything else is tuned at operating temp as would be normal practice. What I realized though is starting cold and allowing the engine to warm up, the air mass model in the PCM is way off(high, so engine runs very rich) and tapers back to correct as the engine warms up. To fix this in a pinch, I'm taking out ~50% of the fuel at 40C and taper to 1EQ at operating temp. This works and keeps the engine from fouling out while warming up.
B3605, OLFA table, in lambda. This works, but I consider it a band aide to a larger problem. This whole tuning process has been overshadowed by what I consider large amounts of desired base airflow and startup airflow. My theory is that if the airmass model is wrong at less than operating temp conditions, and reporting higher than necessary airflow and therefore providing more than necessary fuel, that any sort of RAFPN tuning would be skewed at lower temps and give me the higher numbers. I'll mention, the engine starts fine hot.
For whatever reason, it appears this engine combo is much less efficient at lower coolant temps, so I started looking for a table to adjust the VE based on coolant temp. I found the VE correction factors in the ...604 XDF as well as in HPT. So I ported those tables over to EFI for the ...618 OS and am ready to try modifying them, but I'm realizing I don't understand how the table functions.
The description is that the VE Correction factors in the tables are used to initialize a value, which I figured is then updated. Without a MAF, running speed density I'm not sure how it can be updated? This is where I'm looking for some insight into the OS of the PCM to understand how the values from this table are used within the speed density dynamic air mass calc. Are the correction factors reloaded often from this table? or maybe only at startup? Are these corrections multiplied into the VE table, or divided?
Potentially I can log EQ error correction between commanded and actual and use that to 'tune' in this table for different coolant temperatures. At the least I figure I can set this whole table to 1.0, and set the min and max correction to 0.999 and 1.001 and at least make it one less modifier to get in the way.
If this table isn't what I need to modify then I guess I will stick to looking for a problem with the dynamic temperature calc. Potentially it is an issue with the IAT being mounted in the aluminum intake manifold and instantly heat soaking(single plane carb style intake)....but the IAT is believable as it's just a standard 14" airfilter that draws in underhood air.
Curious what you guys know about how these internal VE corrections are used, and how they are best adjusted for speed density tunes. From what I gather here I can make a plan for my next moves. Thanks!