I've noticed that our F150 simply will not engage the lockup in topgear until it heats up which is typically a good five minutes or more down the road. During this time, economy drops from about 18 mpg to 16. I can only guess that the ATF viscosity is just too high to engage the lockup until warm and that extra 2 mpg is essentially diverted to heat it up. So the question is, will synthetic ATF improve the time lag until lockup is possible?
The cable adjustment should help, yes. I think RH77 played with that on his Acura (unexpected results?) - he may have more to offer.
Bruce- Holy cow, don't forget to tighten it up once you've found a good adjustment! Mine slipped into a tragic "Non-TC-Lockup" situation about a year ago. Man did that suck.
Experiments for me showed that a loose cable gives the tranny less pressure to shift, and could slip and wear prematurely -- also it took further up the RPM band to decide to shift. I have mine tighter-than-stock, and I'm getting great FE results, although with firmer shifts. Does your car have a torque converter?
Slackening off, is, I think he means, adjusting it so that it tugs less on the transmission, so that it registers less throttle input and shifts sooner/doesn't kick down as quickly.
It's actually the opposite for me. Forget that it had popped off of its connection point, and bear in mind that a "Grade-Logic" hill control system is at work here (basically calculation of Load, TPS, and VSS).
I tightened the cable adjuster so that it pulls more on the transmission cable with more throttle input. With the OBD-II feedback loop, it takes the TPS reading and communicates with the TCU. The result is full-TC lockup at exactly 35 mph, whereas stock is closer to 40. A pressure sensor in the transmission will help decide when to make the shift, and with the cable tighter, it upshifts sooner. Downshifts are based primarily on Load and TPS input (generally 45%+ TPS, with 70%+ loads) or, of course, vehicle speed as it slows. As it stands, TC lockup will hold with the added pressure from the cable actuation over the input from the TPS/VSS -> TCU circuit.
Long story short, a shop manual will translate how the transmission "thinks", and what modifications are required to excercise some control over the slushbox.