CheapXJ said:
From what I understand, the TC wouldn't really be able to handle the torque when locked in 1st gear. (thats what I gathered from reading this: http://www.wagoneers.com/XJ/tech/AW4-trans/tcu.html )
It would be nice to have that ability (especially when wheelin' ) but I don't know for sure if it'll handle it. I know how sensitive lockup turque convertors can be to conditions, that why I want it to default to automatic control when not forced to lock.
as far as auto mode for the torque convertor, the existing TCU will take care of that. It'll just be a relay controlled by both the TCU and the switch (diodes on both)
it's keeping the TCU happy, and out of limp mode that might me a problem.
I was thinking delusions of grandeur for another term project (plug in, programmable controller for renix FI that WILL output both running data and fault codes ) but that will be slightly more challenging
:roflmao:
I remember when John was building his first TCU override control switch project (a long XJ-List project thread at the time), and this report is a good summation of the information available at the time (~1997), although some of the assumptions are not totally correct.
<When you come to a stop, either the TC unlocks itself (by nature of how the hydraulic plumbing works) or it bangs a bit, then stalls the motor... usually I flick the switch off before anything happens.>
If you test the AW4 without a TCU the TC lockup will not release through any "hydraulic plumbing" during a stop. It remains locked and is strong enough to stall the engine (I have done this). It is strong enough to stall the engine with a little rpm (1400 rpm, 4hi, and heavy brake application with the axles on stands, BTDT too). It will also smoke the brakes in 4lo. IMO, the locked TC lockup clutch can handle considerable torque, but may not be very reliable if subject to a high frequency of cycle operations (too much heat). Keeping it locked does not allow slip, and no heat, not like constant cycling or without any lockup.
<Putting too much foot into the throttle with the TC locked will give you a quick wake-up call... the TC lock is not intended to handle full engine
torque (remember where your peak torque occurs- fairly low...) and it'll give you a soft jolt if you forget to unlock before feeding too much fuel.>
The TCU appears to unlock the TC when sensing the brake switch, when sensing WOT from the TPS (sometimes), and at a set speed below a threshold as sensed by the speed sensor. There is a reference resistor in the wiring harness that must read by the TCU without bias (no shorting or bypass voltage) to have it lockup the TC.
Footing the moving vehicle at low rpm with a manually locked up TC provides no drama, just a slow progression of acceleration as you move through the powerband (the experience of my testing). I have to grant John credit, as I tested a near new TC, and maybe his TC was tested with 150K miles of wear and slipped (I would not discount what John experienced).
<One thing I will tell you about TC lock- The TCU is programmed to force TC lockup when engine RPMS are above a certain point (?dunno yet?), AND you're at Wide Open Throttle.>
My testing experienced that the TCU will be controlled to unlock at any speed if the brake switch is made. 4000 rpm, touch the brake pedal (short the TCU brake switch input), and the S3 is controlled to unlock the TC. No forced lockup rpm override.
I tried to get it to repeat a WOT unlock that it appeared to do in early tests, but could not, unless it downshifted first (drop to 3rd and unlock at the same time). When I was able to keep it in OD the TC would not unlock at WOT. I would like to hear what others have found in testing?
I did my testing with multiple VOM's reading the S1/S2/S3 voltage outputs, and the inputs to the TCU (backprobed connections on the TCU harness). The speed sensor can be backprobed as well (but I did not have a scope to count the speed of controlled unlock, what I want to be adjustable). I would recommend this exercise to help understand the TCU program sequence of operation.
I would like a failsafe TC unlock in 1st (with an adjustable slow speed unlock) to keep the temps down. The TCU unlock setpoint speed is too high (IMO, even with the 2nd gear override) and not functional in 1st.
I think you have a great project anyway (even if it fails to address an adjustable auto TC unlock).