Help me understand the NAG1 and my problem
Please bear with me for a longish background journey.
I have a 2012 Challenger SXT+ with the 3.6 and NAG1 transmission. Ever since I've bought the car (new) it has hung up on the rev limiter for a second or two at the 2-3 shift and sometimes the 3-4 shift when in drive...Auto-Stick mode works fine and shifts just before the red line. A few years ago, I installed a Vortech supercharger and intercooler, larger injectors and all the necessary support hardware. The initial tune was OK, but since the installation I've added a Getrag posi with 3.73 gears and some other goodies, then had a different tuner tie it all together. FYI, my handheld tuner is a Diablo Trinity2. After a few tweaks to the tune by the tuner, the car is putting down 500 RWHP. No too shabby for a 220 CID V6 at only 8 Lbs of boost.
To help with the shift firmness I installed a transmission tuner of sorts that "piggy-backs" into the TCM wiring harness. It is limited in its capabilities to only adjusting the firmness of the shifts in drive and allows some shift point adjustment in Auto-Stick mode. It helped some by firming up the shifts in drive and really firmed them in Auto-Stick mode. I'm pretty sure this is accomplished by raising the line pressure, but I'm at a loss as to how the Auto-Stick mode shifts are raised.
Anyway the shift problem still exists but after having the tuner raise the redline to 7000 RPMs across the board for each gear, the engine in drive mode now hits the magic limp home threshold with the expected results. I've read that this point is set at 7K RPMs and is non adjustable...is this true? Auto-Stick mode remains fine; firm crisp shifts at about 6800 RPMs. Right where I set them...no problems there. Due to that, I'm having the engine tuner dial the redline back down to 6800 RPMs where the first tuner set it in an effort to keep the car from going into "limp home" mode, but this is only a band-aid and I really need to tune the TCM with a proper tuner.
This where my confusion is. From what I've read, for the 3.6 V6, the factory shift points at WOT in drive are supposed to be set at 6250ish RPMs, so why is it taking almost another 800 PRMs for the transmission to shift (2-3 & 3-4)? And why is it hanging up on the rev limiter for so long before shifting...to the point of hitting the 7k red-line and going into "limp-home" mode?
While I'm waiting for the experts to answer, I'll be reading this thread to try to wrap my mind around this problem.
TIA!
