Engine, ECM, 700r4, TV cable, torque converter 101

[deesandvees]

Can somebody explain to me how the whole engine, ECM & 700r4 talk to eachother in this '87 Caprice of mine? Also, a little info on the tv cable and torque converter would be helpful too. I just don't know how all this stuff effects eachother. Torque converter lockup etc. Thanks.

[silicon212]

The torque converter lockup is controlled by the ECM. There is a 3-wire line that runs from the ECM harness at the back of the engine, down over the bellhousing and to the driver side of the transmission, where it connects to a 4-conductor (only 3 are used) plastic connector on the transmission, facing up, behind the gear selector arm.

The TV cable routes from the passenger side of the transmission, over the bellhousing, to the bracket behind the throttle on the carb.

The ECM harness is designed such that each plug is different and only fits its corresponding connector. There is the harness that comes through the firewall, below the A/C evaporator housing, that comes up and ultimately reaches over the engine, terminating in that TCC line. Along the way, you will see it interface with the:

(on the fender) - Pressure differential/BARO sensor, ECS module, a single blue wire runs from the ECS module to the knock sensor located on the lower right portion of the engine block (on the right water jacket drain - as the drain plug), there is also a fused wire/wires that might run from this point over the engine, to a pressure switch on the power steering pressure line (this is actually a part of the A/C system),

(on to the engine, splits in two, first branch) - Carburetor M/C solenoid, throttle position sensor, coolant temp sensor (on t-stat housing), oxygen sensor,

(second branch) - EGR solenoid, MAP sensor, distributor EST line, TCC solenoid (on transmission, per above)

Three grounds on the engine portion of the harness - two bolt to the front of the intake manifold (a stud on the t-stat housing for example) and one at the rear.

The TV cable is adjusted by pressing in the "D" shaped tang with one hand while pulling all the way back on the cable (toward the firewall) with the other, releasing the tang and then fully opening the throttle on the carb and releasing. You will hear what official literature considers a 'clicking' or 'ratcheting' sound while the cable adjusts - in my experience, this sounds more like gears stripping, but is normal behavior. If the TV spring in the transmission is correct and not worn, this method will properly adjust the TV cable. NOTE - a TV cable adjustment is IMPERATIVE for the transmission to survive. If, when test driving the car, the transmission shifts into 3rd by the time you're at 15MPH, as in shift-shift-shift, PULL OVER and pull that cable back toward the firewall a 'click' or two -it won't hurt to OVERadjust the cable (the transmission will shift later and harder), but it will hurt to have it underadjusted as there is not enough line pressure to hold the clutches engaged under torque.

[deesandvees]

So if I'm eliminating my ECM I'm going to have problems in the Torque Converter lockup department? Can I keep the ECM and have only the wire connected to the trani hooked up and nothing else (and TV cable of course)? Or will I have problems with that, or just dummy lights? How did lockup work pre ECM's? What does "TV" stand for? Thanks Silicon your answers are greatly appreciated!

[PeteA216]

What I did with my TCC when I got rid of my ECM is wire it to a switch on the dash. With the switch "ON" the torque converter will lock up immediately when the transmission engages into 4th gear, and will release immediately when the transmission drops down the 3rd, or when I press the brake medal. I like the switch because when I'm cruising on the expressway and I want to accellerate lightly but don't want to drop down to 3rd gear, I flick the switch to "OFF" disengaging the TCC giving me just enough RPMs go accellerate a little. Flick the switch back on for instant fuel economy.

[silicon212]

TV means Throttle Valve. As the name implies, it is a valve in the transmission, which is controlled by the throttle. It performs two functions in one - detent downshifts (passing gear), and line pressure modulation. It replaced the old vacuum modulator on older units such as the TH350/400.

700R4.com has a kit that will allow you to use the TCC through a pressure switch within the transmission, instead of the ECM. Just add an ignition-on power source to the proper pin on the 4-pin case connector, and the valve will handle the rest.

Pete, by dumping the TCC for passing purposes, you are putting your 3-4 clutch at risk. My 2¢.

[randy78]

with a 700r4 you definitely want to keep the TCC functional

if at all possible

[deesandvees]

What I found out is that I can hook it up so it works off of a vacuum and I'll also need to change the wiring around a bit in the pan. Haven't received the part yet, but it seems pretty straight forward. Luckily I hadn't filled the trani yet.