Using SGII to find converter lock-up release point
 

Hi,

just got my ScanGauge yesterday, and I have been playing a little with it.

I am trying to find a good indicator for how much throttle I can give without the AT releasing the torque converter. I have tried TPS (shows anywhere between 30 to 45 when the lock-up releases, depending on speed, I guess), LOD (about the same as TPS, but a little lower numbers), and MAP (always somewhere around 95-98 kPa as far as I have seen)

It seems that the MAP is the most accurate one so far, but I'm not certain that this is correct. What if I'm at a high altitude in bad weather? I guess the atmospheric pressure could go far below 95 kPa then (as 101.3 kPa is standard atmospheric pressure at sea level), and I think it still would release :)

Any ideas/thoughts?

Not to dishearten even more (because I also want to know the same thing), but it may also be affected by transmission temperature. My car (I know, apples/oranges, but hey, they're both fruit) is MUCH more feisty about locking up when it's really hot outside than on a cool morning.

True, didn't think of that.

I found and read in the service manual for my car (actually minivan, Chrysler Grand Voyager), and googled a bit too. It is possibly a function of a lot of things, like temp, torque, throttle, RPM, acceleration rate, barometric pressure, etc. which makes it pretty much impossible to find a good indicator...

I'll try some more and see if he MAP thing is somewhat consistent in normal driving conditions, or if I have to keep guessing and hoping in every hill :p

It could possibly be affected by engine load. I have noticed when driving my truck that if I have the cruise control engaged, the truck can go up to 100% load while climbing a hill. If I am using the throttle, I can only hit about 92% load before the tranny will downshift.

The speed at which the lockup engages can be determined by watching the tachometer. On most cars the lockup release speed is usually approximately 5 MPH lower than the engage speed.

I have noticed something similar om my cruise as well a couple of times, but this was before I got the ScanGauge, so I don't have any numbers. Sometimes it will bleed off speed uphill to avoid releasing the TC or downshift, but other times it will downshift almost at once the speed drops below set. I have not found any pattern in this, though.