why do shifts and shift times feel different when in SD?

[350SS]

I'm just starting out tuning my truck (98 pickup with 411 pcm swap...4L60E trans) using the Auto VE procedure and have noticed that when tuning in open loop SD and after putting back to closed loop SD after tuning a bit, my shifts feel differen...both in feel and timing. I'm obviously running with the MAF unplugged and the proper changes made to MAF parameters so that codes arent set. But after looking at the transmission tables, I cant really find anything MAF related other than if a code is set, commanding full line pressure, etc. Any suggestions on where to start looking? TIA!

Max

[Chevy366]

I don't know much about 98 models but in a 05 when the MAF fails doing AutoVE tuning it has a increase in line pressure that needs to be turned Off in the Transmission Diagnostic Section E0104 , DTC Fault Pressure Modifier , P0101 , P0102 , P0103 , set to Off .

[350SS]

I'll check that out...Thanks!

[dc_justin]

In addition to the max pressure faults, are you running a bit rich in SD? Shift firmness is dependent on calculated engine torque, which is dependent on RPM, spark timing and airmass calculation. If your VE table is a bit higher than it should be, then the airmass calculation will be high, calculated torque will be high and shift firmness will be higher than normal.

[hquick]

Thanks Justin,
I've been wondering the same thing. Seems we're at about the same stage Max.
I haven't had this issue this time but last time, before using EFILive (JET DST) I was experiencing the very firm shifting whilst in SD mode.
More great info.

[350SS]

I don't know much about 98 models but in a 05 when the MAF fails doing AutoVE tuning it has a increase in line pressure that needs to be turned Off in the Transmission Diagnostic Section E0104 , DTC Fault Pressure Modifier , P0101 , P0102 , P0103 , set to Off .
I recently switched to COS1 SD and changed these values according to the COS tutorial section Going MAFless. Seems to have made the difference and shift feel and timing are back to normal ;) Thanks guys!

[350SS]

In addition to the max pressure faults, are you running a bit rich in SD? Shift firmness is dependent on calculated engine torque, which is dependent on RPM, spark timing and airmass calculation. If your VE table is a bit higher than it should be, then the airmass calculation will be high, calculated torque will be high and shift firmness will be higher than normal.
Thanks for the tip...I'm really new to tuning, and that seems like something I'll want to be looking out for when I'm perfecting my VE table :master:

:beer: Max

[4.8t]

i was told on hptuners forum that only 98-00 pcm revert to full line pressure. is this correct?