Part 2 Testing: The CompuShift Plus performed as advertised when the unit is used to hold the vehicle in second gear when decelerating/coming down a grade. A small quirk was noted and this situation is clearly stated in the installation manual. (In fact the manufacturer or CompuShift emphasizes that a buyer should return the unit for a full refund if they could not live with this quirk.)
The Cherokees on board diagnostics senses that the transmission is not in the proper gear and the “Check Engine” light comes on. Research confirms that this in no way hinders the operation of the transmission. It is caused by error codes that tell the on board diagnostics that the transmission is not in the proper gear as determined by the computer. The fact that this only an indicator light problem was verified by the testing in numerous field situations. The light will go out after driving the vehicle through three “trip cycles” which includes starting the engine, accelerating through the gears, however this really isn’t necessary. It should be noted that until recently vehicles did not even have a “Check Engine” light. Note: The “Check Engine” light is only an issue with 1996 models and up. There is consideration of more consequence if the CompuShift Plus is going to be used by the serious 4x4 user. When the test vehicle encountered a hill of any magnitude an unexpected and sudden downshift to low occurred rather than staying in second gear as desired. The result, when climbing a loose slope, was wheel spin and loss of traction. The writer talked at length with Jim Nasset, the inventor and developer of the CompuShift Plus, about this and other aspects regarding his unit. (It should be noted that he was extremely helpful and is genuinely interested to marketing a good product.) He instructed the writer on how to wire the unit so that it would not downshift out of second to first until the switch was flipped back to the normal operating position. These instructions are now being included with the CompuShift Plus. He indicated that the shift-down feature was included as a safety measure for individuals who might be pulling trailers and not remember to deactivate the CompuShift Plus which would result in excessive lugging. He also understood as to why the serious off-roader would not want this feature. The writer was completely satisfied with the operation of the CompuShift Plus once this change was made. Many miles of moderate to severe back roads have now been traveled in low range by shifting back and forth between low and second using the CompuShift Plus switch and then using the shift lever to select third or drive for faster sections. Jim’s instructions for eliminating the automatic downshift are included for those readers who might want to modify an existing unit. “All you need to do is to connect the Blue and Orange wires together to eliminate the throttle kick down. (Make sure to not leave the original orange wire connected to the transmission control module.) This will work on the 87 to 95 models as well as the 96+ Cherokees.” One other item of note occurred when using the CompuShift Plus on the author’s 1997 Cherokee. It appears that the torque converter lockup is engaged in third gear after using the CompuShift Plus in the low/second mode and then returning to third or drive for normal driving operation. The only indication of this is a slight decrease in torque and an accompanied reduction of RPM in third gear as indicated by the tachometer. Most users probably would not even notice it has occurred and it is easily corrected by merely turning the ignition switch off, and then restarting the engine. It should be noted that this may not occur with all late model Cherokees and, in fact, may only occur on this particular test vehicle as the AW4 electronic controls are quite complicated and a completed diagnosis was not possible. The writer spoke with several mechanics that were quite familiar with this transmission and it is probable that the error codes that trigger the “Check Engine Light” also create this symptom. They also felt that it was not something to be concerned about. The author would like to request that any readers who have noticed a similar occurrence please contact Jim Nasset, the developer of CompuShift Plus. It was also noted that there was a momentary lag when shifting to third gear. Jim noted that this characteristic is typical of the AW4 transmission and the only way to avoid it to accelerate to around 35 mph (12 mph in low range) before shifting into third. This lag did not present any particular concern to the writer. The unit performed flawlessly after the switch was rewired to give total control of the shift points. The tester found that challenging 4-wheel drive trails were a pleasure to drive by merely using the CompuShift Plus switch to shift back and forth between low and second. The shift lever is then used to select 3rd and 4th without disengaging the CompuShift Plus. The transmission no longer slams into low gear when one is descending a steep grade in second gear and then slows up for an obstacle or tight turn. Challenging long hills, with poor traction, could now be climbed that were not possible before. This was because the grades could be climbed in second gear, low range without an automatic downshift to low that resulted in wheel spin and loss of progress. It is also important to note that the CompuShift Plus comes with a lifetime warranty. If the unit should ever fail, a user has only to send it back to Aftermarket Innovations and it will be tested. The CompuShift Plus will then be replaced if found to be defective. Conclusions: Safety is more important than convenience! The author will gladly put up with the “Check Engine” light quirk as long as he can have control over the transmission! CompuShift Plus provides the transmission control that the Chrysler/Jeep engineers left out. This is definitely a “must have” for any serious 4x4 enthusiast who has a Jeep with the AW4 transmission.
Contact/Ordering Information:
5820 Brooklake Road P.O. Box 9031 Brooks, OR 97305 800-528-6900 http://www.cherokee-jeep.com/ jimnasset@earthlink.net
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