Success!
**Not sure if this should be posted here or in a separate thread. I'll start here and re-post elsewhere if requested/required.**
I performed a few experiments last night, and was very pleased with the results. While I still have a few more tests to run, the important questions have been answered in the affirmative. And that means I will be able to install a full-featured aftermarket manual shifter in my XJ (98 model, stock 4.0L & AW4) that will
not set a diagnostic code and/or light the CEL. :yelclap:
I received my RADdesigns Rail Shifter yesterday, and set straight to work. First, I needed to confirm two things on which my plan depends:
1. Can simple resistors be connected between the 3 solenoid outputs of the Transmission Control Module (TCM) and ground to act as dummy loads without the TCM throwing a code and lighting the CEL?
Yes. This was tested by simply cutting the 3 solenoid output wires in the harness near the TCM plug, and directly wiring a 12 Ohm, 50W resistor between each wire (on the TCM side, obviously) and ground. Started the Jeep and waited. Drove up and down the driveway a few times. No CEL. No problems. It works!
2. Can the TCM be switched back and forth between the dummy resistors and the tranny solenoids with the motor running and the transmission in gear without the TCM throwing a code and lighting the CEL?
Yes. This was tested by using the schematic below. A DPDT relay is used to switch each TCM solenoid output between the real and dummy loads. Note the break-before-make configuration assures that the TCM output transistors never see both loads simultaneously, which would obviously double the current draw. They do, however, see no load at all for a fraction of a second -- and that's what this test was all about. Would that brief no-load condition cause a code/CEL? Fortunately, it did not. The relays are controlled by rocker switches. Drove around the block several times, switching back and forth between manually sifting with the RADesigns Rail Shifter, and letting the TCM do it's full-auto thang. No CEL. No problems. It works!
I ran out of time, and was unable to hook up and test the TC part (orange wires, SW3, RY3, etc.), but it should work fine. It's fundamentally the same circuit.
A few additional observations:
1. Manually shifting the AW4 is
SWEET. Now I understand why so many have reported in these forums that they actually prefer shifting it manually, even during daily driving. It's something you simply have to experience first hand.
2. The RADDesigns Rail Shifter is smaller than it appears online. It should be easier to mount/locate than I had feared.
3. The 12 Ohm resistors get
really hot. I'm hoping that kastein's theory is correct, and that higher value resistors can be used to reduce current draw. Using the metal knee blocker under the steering column as a heat sink will probably alleviate the problem, but using higher-Ohm resistors would make for a far more elegant solution, if they work. Will test and advise.
4. The schematic can be easily adapted for use with any sort of manual shifter and/or a home-brew creation of your choice.
5. It should be noted that the testing was very brief -- less than 20 minutes driving time total. As such, I can't swear that this is the final solution but it sure feels like a major step in the right direction. I thought it was worth sharing.
Schematic:
Discuss.