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+--- Thread: 722.6 tuning (/showthread.php?tid=6698)
722.6 tuning - whipplem104 - 08-24-2015
I have been getting a few questions about tuning issues with various systems besides the PCS system that I sell. I am happy to help when I can. I did want to say that I really do not pay much attention to the various versions of the transmissions. Mostly just large nag vs small nag and then I build to suit.
I figured I would post up some basic operating principles to help everyone understand this a little more regardless of the system.
1st off the transmission is a sequential transmission. Meaning that it has to shift 1-5 and 5-1. No skip shifting. If it misses a shift and continues through the shifting sequence that is a problem. The only way to diagnose a missed shift is ration calculation. Via and input and output speed on the transmission. The two internal speed sensors are planetary speed sensors and depending on what gear you are in both are used for input speed. The factory uses wheel speed of the rear two wheels in rear wheel drive vehicles and averages them together and then multiplies by the rear differential ratio to get driveshaft speed. Without this data you need to measure driveshaft speed with a sensor. I supply speed sensor kits with my packages for this purpose.
Ok now we know what gear the transmission is in. Instead of just hoping that it did what we told it to.
In basic hydraulic operation if you start the car with no computers hooked up and put it in drive the transmission will be at full pressure and go into 2nd gear when D is engaged.
To put the transmission into 1st gear you must perform a 2-1 downshift.
Now pressure control.
There are two pressures to control with the tcm. Modulator and Shift pressure. These then in turn control other pressures in the transmission. Modulator pressure controls the total working pressure in the trans. which is the supply pressure for all other pressures or pump pressure. At low modulator pressures you can start to reduce the supply pressures for other functions. Including the pressure supply for the Mod and Shift pressure solenoids. So Mod pressure can effect Shift pressure.
Shift pressure is simply that. The pressure that acts on a clutch pack to fill an oncoming clutch. Once a shift is over it no longer does anything.
Mod. pressure acts as the overlap control during a shift as well. What is overlap control? It controls the drain rate of the clutch that is turning off during a shift. This is mostly important in the 3-4 shift. It is a clutch to clutch shift and if you drain b2 to fast then the transmission will go into neutral before k3 has started to fill and hold.
How do these pressures get controlled? Both are PWM duty cycle. The higher the duty cycle or amperage the lower the pressure will be.
The shift solenoids simply activate when a shift begins. When it ends is totally dependent on the pressure and power being pushed through the gear change. Do not underestimate the inertia and engine has at higher rpms as well. Really what you are tuning for is torque and TPS is a very poor way of measuring torque.
Torque converter lock up.
Do not try and lock up torque converters at low rpms under heavy load. It will destroy the converter clutch. If you are running the PCS tcm then you can monitor torque converter slip. Depending on load you want to lock up the converter at or near when slipping is at its minimum. So you can imagine the lower the throttle the lower the rpm you can lock the converter up and the higher the throttle the higher the rpm. Most converters in Mercedes are going to be pretty much within 5-7% slip at full throttle by 3500 rpm. But I normally lock up mine at full throttle at the top of 2nd or 3rd gear.
Pressure control for the converter lock up is working pressure supply. The PCS system and others I imagine are simply turning on the lock up solenoid. Floating it for a slip function is nearly impossible. I am working on that with the new tcm but still not there.
Hope this helps.