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Using a New Transmission with a MegaShift™ Controller

The MShift™ code is set up so that different transmissions can be supported with user parameter changes, and code changes are not normally required. The default user parameters for MShift™ are for the 4L60E 4-speed automatic transmission from General Motors. These parameters are saved in MSQ files by the tuning software. Other users may have MSQ files suitable for your transmission available from this site or from the MShift™ forum.

Other transmissions may require some homework on the part of the user to set these parameters.

Below is a list of the information needed to operate any 8 (or fewer) forward speed automatic transmission using a MegaShift™ controller. Links to the appropriate section of the manual are provided in the explanations. The main information needed to use any trans with a MegaShift™ controller is:

  1. How many solenoids control the shifting?

    A 4-speed requires at least two shift solenoids to operate, 5 speed to 8 speed trans require at least 3; the MShift™ controller has up to 8 solenoid outputs (9 outputs with code), though some will need hardware additions/modifications. In addition to the 3 standard shift outputs, there are two spare ports (three with 4.1xx+) that can be used for solenoid control optional shift solenoid output circuits, plus two more outputs that can be used if a voltage based manual shift lever input is used. The 4L60E, for example, uses two shift solenoids and a 3/2 solenoid. These shift solenoids put the transmission into the appropriate forward gear. In the MShift™ controller, these solenoids are controlled by Output1, Output2, Output3 (and Output4 if enabled). They are controlled by grounding the solenoid to allow current to flow through the solenoid. Whether the circuit is open or grounded in each gear is set in the Shift Output Patterns menu in the tuning software.

    Note that neutral, park, and reverse are normally selected by the manual shift lever, however the user can specify the shift solenoid states for these gears in the tuning software.

  2. Which shift solenoids are on, and which are off in each gear?

    You will need to determine which solenoids are on and off to place the transmission into each of its forward gears. Because the shift solenoids must specify a particular forward gear, the patterns for each forward gear must be different from any other forward gear. This is critical - you must get this right, as the transmission uses this info both to put the transmission into gear, and to determine which gear it is in.

    For example, for the 4L60E, the output patterns (which are the MShift™ controller defaults) are:

    Gear SolA (Output1) SolB (Output2) 3/2Sol (Output3)
    P "on" "on" "off"
    R "on" "on" "off"
    N "on" "on" "off"
    1st "on" "on" "off"
    2nd "off" "on" "on"
    3rd "off" "off" "on"
    4th "on" "off" "on"

    Note that in 1st through 4th gears the patterns of the SolA and SolB solenoids are unique.

  3. Are any solenoids on only during shifts?

    If so, you will need to use one or both of the spare ports as 'clutch outputs', the behavior can be set under 'Shift Logic Patterns/Clutch Pattern1/2'.

  4. Are any or all of the shift solenoids pulse width modulated (PWM'd)? If so, at what frequency and duty cycle? Is there a 'refresh' booster cycle on the PWM?

    Pulse width modulation is used to limit the current through the solenoids, or to partially engage a solenoid (typically to engage it slowly). Using too much current will burn the solenoid, too little current may cause it not to work at all. So you will need to get these values close to correct if you wish to have a fully functional, reliable set-up. This information is sometimes available in factory service manuals (though it may be in the form of a DC resistance and a maximum current - so for example if the DC resistance is 5.6 Ohms, and the maximum current is 1.51 amps, then with a supply voltage of 14.5 Volts, the PWM duty cycle (DC) must be no more than DC = I*R/V => DC = 1.1*5.6/14.5 = 0.425 = 42.5%). Since this is a maximum, you might use 40% in the shift solenoid PWM set-up.

    Refresh is used to minimize the PWM by some original equipment manufacturers. Just before the solenoid would close, an additional PWM refresh cycle is applied to keep it open. This may allow running less current through the solenoid overall.

    The default in the MShift™ code is for the PWM to be off for output1 and output2. If PWM is enabled for these, the default PWM parameters are for the Chrysler 41te 1.96kHz shift solenoids. If refresh is enabled for these, the default refresh parameters (100% for 8 milliseconds every 50 milliseconds) are for the Chrysler 41te shift solenoids as well.

  5. How many solenoids control the torque converter clutch lock-up (usually one or two)? Are either of these PWM'd? Is the TCC engaged when the solenoid is connected to ground, or to 12V?

    Typically one solenoid is used for TCC control. However, some early transmission may use no external TCC control, and some later transmission may use 2 TCC control solenoids. In the MShift™ controller:

  6. How is the line pressure controlled? If this is done electronically, is line pressure increased or decreased with PWM? Is there a 'dither' cleaning pulse in the PWM? Is there a line pressure sensor?

    Line pressure may be controlled by a solenoid (but not always). When line pressure is electronically controlled, it is typically controlled by PWM'd a 'bleed' valve. That way, if the solenoid fails or a wire is broken, full line pressure is applied at all times.

    You can set the pressure control (PC) PWM cycle time under PC PWM Period to match the value expected by your pressure control solenoid (this frequency may be in the factory service manual).

    The MegaShift™ controller has a 16x9 (speed x load) line pressure table to let you set the line pressure. This table is set as 100-PWM%. That way, higher numbers in the table mean higher line pressures. The values can run from 0 to 60% PWM, resulting in table values from 100% to 40%.

    You can also set the Maximum Shift Line Pressure, and then the line pressure PWM% during a shift will be the lower of this value or that in the 12x12 table.

    The code has provisions for line pressure monitoring. The default is for a 0.5-4.5V line pressure sensor using an internal table to determine the pressure from the voltage. If another pressure sensor is used, a different table can be burned to the MShift™ controller.

    Dither is a cleaning pulse applied to the pressure control solenoid, it is held high for longer than the PWM would normally allow, this allows extra fluid to circulate during times of extended low loads. The dither pulse is not enabled by default. If enabled, the default MShift™ dither values are for the GM 4L80E.

  7. What sort of signal does the shift lever send to the MShift™ controller to tell the trans what gear the driver has selected? Is it 3 or more digital (on/off) switches, or a varying voltage?

    With the 'Manual Lever Mode' setting, you can choose if the MShift™ controller uses:

    If your transmission uses digital inputs, you need to specify unique patterns for each and every gear (including park, neutral and reverse) in the 'Shift Input Patterns'. So you will want to be certain of the patterns your transmission puts out (this is often in the factory service manual).

    If your transmission uses a voltage based shift lever scheme, then you have to specify the voltage in each gear. MShift™ will determine the range of voltage from the values entered. So specify the middle of any applicable range if that's what you are able to find (this is often in the factory service manual).

  8. How many teeth are on the wheel for the VSS sensor?

    The vehicle speed sensor (VSS) tells the MShift™ controller how fast the vehicle is traveling. The MShift™ controller uses the 'number of teeth' parameter to determine the rpm of the output shaft (and factoring in the tire diameter and rear axle ratio it computes the vehicle speed).

    It uses this information for shifting, line pressure control, TCC lock-up, and a number of other important functions. So you will want to get the number of VSS teeth correct. However, if you can't find this value, you can 'calibrate' it later by entering the info you do know (such as the tire diameter and axle ratio), guessing your number of VSS teeth, and then comparing your speed to a known reference (mile post markers, another vehicle, GPS, etc.).

The tuning software guide to all the tuning parameters used for setting up and tuning a transmission using the V4 code is here: V41tune.html. However, not all optional parameters can be chosen simultaneously. Some options preclude the use of others.

If additional specific controls are needed to run your transmission, please discuss these requirements in detail on the MShift™ forum. If it is possible and there is sufficient demand, the new functions will be added to the code.

Once you have the operating parameters for you transmissions, you will need to sort out the electrical requirements. These have a direct bearing ion the build specifications for your GPIO board and the resulting BOM. There are lots of details on the GPIO circuits here:

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© 2010, 2013 Bruce Bowling and Al Grippo. All rights reserved. MegaSquirt® and MicroSquirt® are registered trademarks. This document is solely for the support of MegaSquirt® boards from Bowling and Grippo.