WJ Torque Converter Clutch not engaging.

[groenconrad]

Jeep Grand Cherokee 4.7 HO (5-45rfe Transmission)

About 2 years ago I noticed that my torque converter clutch (TCC) only locks up after about 25 minutes of highway driving. A few weeks later I took a trip to the Eastern Cape and while slowly accelerating up a long hill the Check Engine Light came on with a fault code P0700. Using my OBDII wireless scanner together with my phone I was able to get the more detailed code of P0740 (Torque Con Clu No RPM Drop at Lockup; Relationship between engine and vehicle speeds indicated failure of torque converter clutch lock-up system (TCC/PTU sol), this test apparently is only done by the TCM in 3rd gear) I immediately reset the fault code and it never resurfaced, until recently.

Back home I did some reading and found a plethora of possible causes from online forums. Starting with the simple and easy fixes I have done the following:

June 2016. Input speed sensor (no change)

July 2016. Output speed sensor (no change)

July 2017. Developed a hard shifting between 2nd and 3rd (both up and down shifting) and the MIL with P0700 came back.

August 2017. Oil and filter change plus replaced the Line Pressure Sensor. (fixed the hard shifting), at this service I was told that the TCM stored a Trans Over Temp fault, however the Trans Over Temp warning light never came on. The old line pressure sensor's tip was bent, maybe due to high temps?

April 2018. Over the past two years my fuel economy slowly deteriorated and my engine was loosing power. Took the Jeep to Anton Slabbert at APS in Stikland who diagnosed it with a blocked fuel filter. APS was hopeful that the poor torque from the engine due to fuel starvation might also be the reason for no lock-up on the TCC. Power restored with new filter, but unfortunately no TCC lock up.

Other possible causes according to the internet:

Worn TCC plates. (Doubtful)
Faulty TCC solenoid. (Doubtful)
Low fluid pressure due to a faulty pressure regulator pump.
Transmission Temperature sensor. (How would I test for this)
Throttle Position Sensor.
Brake Pedal Switch.
Alternator noise.
Severe engine misfire. (I do seem to have a slight misfire)

Recently drove to Malmesbury and achieved full lock up after about 30 minutes. On my way back the MIL came back on a long uphill and the shifting between 2nd and 3rd is getting harder/rougher. Maybe the Trans overheated again and damaged the Line Pressure Sensor, which could point to a faulty Trans Temp Sensor?

So now I ask for the collective knowledge of this forum to come together and help me fix this problem.

[groenconrad]

The following is from the workshop manual.

TORQUE CONVERTER CLUTCH (TCC)
The TCC (Fig. 114) was installed to improve the
efficiency of the torque converter that is lost to the
slippage of the fluid coupling. Although the fluid coupling
provides smooth, shock-free power transfer, it is
natural for all fluid couplings to slip. If the impeller
and turbine were mechanically locked together, a
zero slippage condition could be obtained. A hydraulic
piston with friction material was added to the turbine
assembly to provide this mechanical lock-up.
In order to reduce heat build-up in the transmission
and buffer the powertrain against torsional
vibrations, the TCM can duty cycle the L/R-CC Solenoid
to achieve a smooth application of the torque
converter clutch. This function, referred to as Electronically
Modulated Converter Clutch (EMCC) can
occur at various times depending on the following
variables:
† Shift lever position
† Current gear range
† Transmission fluid temperature

† Engine coolant temperature
† Input speed
† Engine speed

TORQUE CONVERTER CLUTCH (TCC)
In a standard torque converter, the impeller and
turbine are rotating at about the same speed and the
stator is freewheeling, providing no torque multiplication.
By applying the turbine’s piston and friction
material to the front cover, a total converter engagement
can be obtained. The result of this engagement
is a direct 1:1 mechanical link between the engine
and the transmission.
The clutch can be engaged in second, third, fourth,
and fifth gear ranges depending on overdrive control
switch position. If the overdrive control switch is in
the normal ON position, the clutch will engage after
the shift to fourth gear, and above approximately 72
km/h (45 mph). If the control switch is in the OFF
position, the clutch will engage after the shift to
third gear, at approximately 56 km/h (35 mph) at
light throttle.
The TCM controls the torque converter by way of
internal logic software. The programming of the software
provides the TCM with control over the L/R-CC
Solenoid. There are four output logic states that can
be applied as follows:
† No EMCC
† Partial EMCC
† Full EMCC
† Gradual-to-no EMCC
NO EMCC
Under No EMCC conditions, the L/R Solenoid is
OFF. There are several conditions that can result in
NO EMCC operations. No EMCC can be initiated
due to a fault in the transmission or because the
TCM does not see the need for EMCC under current
driving conditions.
PARTIAL EMCC
Partial EMCC operation modulates the L/R Solenoid
(duty cycle) to obtain partial torque converter
clutch application. Partial EMCC operation is maintained
until Full EMCC is called for and actuated.
During Partial EMCC some slip does occur. Partial
EMCC will usually occur at low speeds, low load and
light throttle situations.
FULL EMCC
During Full EMCC operation, the TCM increases
the L/R Solenoid duty cycle to full ON after Partial
EMCC control brings the engine speed within the
desired slip range of transmission input speed relative
to engine rpm.
GRADUAL-TO-NO EMCC
This operation is to soften the change from Full or
Partial EMCC to No EMCC. This is done at midthrottle
by decreasing the L/R Solenoid duty cycle.