1999 explorer sohc torque converter lock up

[custimguitarman]

Has anyone installed a manual T.C. Lockup on their explorer? I'm looking for wire location on the vehicle so I can tap in.

 

[2000StreetRod]

why do you want to?

Why do you want to manually lock the torque converter? If you lock it manually you'll have to unlock every time your vehicle stops or the engine will die. Doesn't your PCM/5R55E work properly?

 

[custimguitarman]

I don't like the way it unlocks every single time you let off the throttle. I am well aware of the extra attention this mod requires. I wanted to know where the connector is and what color wire to tap to.

 

[2000StreetRod]

TCC solenoid

It appears from the wiring diagram that the PCM activates the torque converter clutch (TCC) by grounding the VT/YE wire between the 5R55E and the PCM.

5R55E C177 pin 5 > C118 M/F pin 15 > PCM C202 pin 54

Unless you electrically isolate the PCM connection from your manual switch control the PCM may detect that the signal is low when it should be high. I don't know if there is a danger of damaging the PCM control circuit by shorting it to ground when the PCM wants it high. That's another reason to electrically isolate the PCM control from your manual switch control.

 

[2000StreetRod]

Brake on/off switch?

I don't like the way it unlocks every single time you let off the throttle. I am well aware of the extra attention this mod requires. I wanted to know where the connector is and what color wire to tap to.

Your symptoms may be due to a failed brake on/off (BOO) switch. If the BOO switch is failed on the converter clutch will not engage at less than 1/3 throttle.

 

[custimguitarman]

I believe everything is working properly but where I live it's semi rural and winding. If you spend a lot of time between 35-50 you are constantly on and off the throttle. Rolling down a small grade and the easing back in the converter is unlocked until you get back close to 45 which to me seems highly unnecessary and annoying. There's no reason that it cannot stay locked and save the high rpm slip until lock up. I feel in this setting a locked converter could offer better fuel mileage. My engine makes plenty of low end torque to justify staying directly coupled until stopped.

And to reply about the direct shorting,
I am looking at a schematic that applies a resistor so the PCM sees a load and does not fault out or become damage.

 

[custimguitarman]

So we are certain the PCM supplies battery negative to the TC circuit and that there is a fixe battery positive already applied to that circuit? If so there are a couple schematics floating around that quite simply cannot be right. ThIs is important!

 

[2000StreetRod]

PWM solenoid

So we are certain the PCM supplies battery negative to the TC circuit and that there is a fixe battery positive already applied to that circuit? If so there are a couple schematics floating around that quite simply cannot be right. ThIs is important!

According to my ATSG 5R55E manual "The converter clutch pressure plate is applied and released by fluid pressure, which is controlled by the Powertrain Control Module (PCM). The PCM controls the torque converter clutch using a pulse-width modulated TCC solenoid."

According to my 2000 Explorer Mountaineer Ford Wiring Diagrams the TCC, EPC, and shift (SSA, SSB, SSC, SSD) solenoids receive battery voltage via LB/OG wire from the PCM relay in the Battery Junction Box. The other end of each solenoid has a dedicated wire to the PCM. I assume that the PCM controls the solenoids using electronic switches to provide a path to ground this energizing the solenoids. In the case of the TCC and EPC the PCM alters the duty cycle to control the position of the solenoid in a manner similar to how it controls the EGR vacuum relay. You could monitor the waveform with a scope to verify.

Where is the resistor supposed to be added and how is it supposed to work? What is the value of the resistor?

 

[2000StreetRod]

solenoid resistance

Below are the specified and actual resistances of my solenoids:

EPC: 3.1 to 5.7 ohms, actual = 4.7
TCC: 8.9 to 16 ohms, actual = 10.1
SSx: 22 to 48 ohms, actual = 25.2 to 25.4

 

[custimguitarman]

Streetrod,
Here is my take on the idea now that you have confirmed a few things for me.
1) the PCM simply gates the solenoid to ground using a transistor connected to ground. It may pulse that connection to act as a buffer or " modulator" to help the plates and other components be happy and also to address the old shudder problem.
2) a resistor plumbed in on the line continuing to the PCM is to simulate a load I.e the solenoid. There is a decent pic of this somewhere and it escapes me at the moment but you have to use a DPDT switch to use it. When you switch to manually lock the T.C. The switch also connects the resistor from a 12v supply to the line going to the PCM and makes it think there is still a solenoid connected. I would suspect a resistor of close to the value of the solenoid's resistance.
I've read that the only real danger is that when you manually lock up and take that voltage away from the PCM it blinks the OD light to represent a fault. Otherwise you could just splice in on the v/y wire and go to a single pole single throw and send I to ground. The PCM already sends that wire to a ground so you really wouldn't be " shorting" the PCM to ground but rather the solenoid before the PCM .

 

[2000StreetRod]

plausible implementation

Your description sounds reasonable. The PCM path to the TCC solenoid is diverted to a resistor in series to battery voltage while the actual connection to the TCC solenoid is diverted to ground energizing the solenoid. The PCM detects the voltage switching from battery voltage to ground and "thinks" the circuit is functioning normally under PCM control. The resistor value should be equal to or greater than the solenoid resistance (16 ohms).

However, there may be more subtle issues. I seem to recall the PCM compares the engine rpm to the turbine shaft speed and the transmission output shaft speed. If the converter is locked when the PCM is commanding it unlocked the output shaft speed will be greater than expected. The PCM may set one of the following Diagnostic Trouble Codes:

P0715 Input/Turbine Speed Sensor Circuit Malfunction
P0720 Output Speed Sensor Circuit Malfunction
P0720 Output Speed Sensor Circuit Malfunction

or something similar.

 

[2000StreetRod]

easiest access

Probably the easiest access to the purple/yellow wire is near the C177 connector under the vehicle in front of the transmission range selector.

C118 is between the rear of the engine and the firewall and difficult to access.

The wire from the PCM to C118 starts out in a bundle at the firewall that I wouldn't want to open. It may break out to smaller accessible bundle as it heads downward along the firewall toward the C118 connector.

 

[custimguitarman]

Streetrod,
You've been far more helpful than I expected to find on here,
Great forum, great people.
Thank you!
I have penned a schematic using two 8 pole ( DPDT) relays and a simple push button. I plan to use a brake switch to " dump" or unlatch the relays so the converter lock- up needs not be thought of when coming to a stop or slowing. This is exactly like the cruise control. Should have been a no brainer. All the schematics I see still require the driver to be completely focused and in control of lock up. Imagine if cruise was this way!

The only reason I went with two 8 poles is to also throw in that resistor I mentioned earlier. Otherwise , according to others, you get a blinking OD light but that's all. I figure why not just solve it straight away.

I'll keep you posted as to how it pans out.
Mike

 

[2000StreetRod]

BPP switch

The brake pedal position (BPP) switch is a double pole double throw switch. One section (LG wire) goes to the stop lamps. The other section (RD/LG wire) goes to the PCM and many other components (speed control servo, 4WABS, RAP module, shift lock actuator, ARC, CPP, GEM). An easy way to test that section is to engage cruise control and tap the break pedal to see if cruise control disengages. I suggest you use that signal instead of the brake light signal.