Taking a quick look it appears the tables saying psi are wrong in this xdf like it is in other definitions. The 4L60e operates at 200psi plus so how can 90psi make sense for a maximum line pressure? With the max pressure scalar left set at 90psi, the code will take the main pressure table and then add any modifier table values before looking the answer up in the force motor table and applying that current to the line pressure. The "psi" adding the tables together is basically divided by the max pressure scalar so increasing the max pressure and increasing the tables would actually do nothing useful.
Last edited by lionelhutz; 08-28-2014 at 09:59 PM.
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Last edited by billygraves; 06-30-2019 at 06:20 PM.
Which IMO is the reason you should really attach a hydraulic pressure gauge when calibrating the line pressure tables. With the plethora of stock and aftermarket pressure regulators, springs, field adjusted EPC solenoids, etc it is entirely possible to have too little or too much pressure.
Like all of Billys posts about these transmissions, this one is GOLD!
On tuning: I have done more trans tunes than I have engine tunes, most of them on 4L60Es in LS vehicles, but the basics have always been the same. Start with shift times. Lower them in the 1-2 and lower or zero them in the 2-3-4. Then adjust shift points. THEN if it feels a bit soft in the shifts, bump up the pressures a few PSI. Finally, clean up any light throttle shifts that are too quick/harsh. If done right it'll drive like a completely different vehicle.
I really prefer to leave the pressure alone in the tune and have a shift kit and (sometimes) servo installed to firm up the shifts, but that is a totally different discussion.
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1991 2500 Suburban Adventure truck - 4wd conversion, 4-link F/R, 582ci CNP Big Block with Terminator X EFI backed by a 6L90 and twin stick'd NP205 t-case
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1979 16' Action Marine/"Johnny Cash" Merc Bridgeport Champ Motor - Metalflake Maniac
No, I didn't miss how the transmission pressures are set in the calibration. As I posted, the xdf says psi in a number of places but all the tables and scalars for the line pressure are not psi. The tables all work together to come up with a number that refers back to the force motor tables and then the force motor current from the table is applied to the force motor. The current in the force motor is what sets the line pressure. PTS is nice to know but it doesn't really matter what it's called as long as everyone realizes what is actually happening.
In $EE increasing the maximum pressure scalar (the one normally set to 90 "psi" actually causes the line pressure to drop. I suspect the same would happen in this calibration.
Yes, the reverse pressure is different but I never bothered to mention the reverse pressure being high, because it is what it is and doesn't affect the pressure during normal forward driving (pressure when shifting and pressure between shifts).
I already knew that the xdf files for the older stuff all come from reverse engineering the calibration code.
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