I know it is activated by a selonid, but what give the selonoid the signal? Is it the computer? What triggers it?

The ECM decides when to lock the TCC based on data from the CTS, TPS, MAP, VSS and 4th gear switch

Should, could it lock before 4th gear?

Yes, the 700R4 is capable of locking in 2nd, 3rd, & 4th. With the ECM in control of the TCC lockup points it is rare to lock in 2nd. Usually need to hold 2nd to prevent an upshift, then once above 30-35 MPH (whatever is programmed into the ECM), it will lock in 2nd.

Most of the time it will lock once in 3rd, then again in 4th.

RBob.

hey rbob would u happen to know what conditions would have to be met for the ecm to lock up the converter in 2nd gear,ever since ive installed my 4k converter ive been having issues with the ecm locking up the converter in 2nd gear right before it makes the 2-3 shift

actually let me rephrase that, if im driving normal with the gear lever in od it locks up during the 2-3 shift.
if im manually shifting at part throttle it will lockup in 2nd before the i move the lever to shift into 3rd
if im wot its fine

In the case of locking in 2nd it is a combination of MPH & TPS. At WOT the TPS setting is preventing lockup, which is normal (until the forced lock MPH is hit and the TCC locks no matter what the TPS is).

For the current locking at/before the 2-3 shift, the vehicle may now be exceeding the lower MPH 'it is now OK to lock threshold' while still in 2nd. If so raising the threshold a few MPH will prevent this locking in 2nd.

Or, it may be that the TPS is a little lower with the higher stall. And it is now allowing it to lock in 2nd at a lower MPH. In this case changing the lock table TPS threshold (vs MPH) will do the trick.

RBob.

thnx rbob, one more ? is forced lockup computer controlled or is it mechanically built into the transmission, in other words if i throw a toggle switch into the lockup circut to disable it until i want to lockup the converter, will it still lockup the converter at said mph?

The forced MPH lockup is in the ECM. Opening the line from the ECM to the TCC will eliminate all but one possible lockup condition. When in high gear (OD) some 700R4's will lock the TCC via a transmission high oil temperature switch. This is located on the valve body and is tied into the under-pan trans wiring.

RBob.

thnx for the info rbob,heh time to go wire up a manual switch now,cause this 2nd gear lockup is really anoying as it the automatic lockup @ wot, that one actually dosent hurt anything but im afarid my converter wont be able to take the abuse for to long at the power levels this thing is making

I think this may be torque converter related...If I'm cruising at say 90 mph and then let off the gas pedal. The car slows down and right at 75 mph there is some sort of change. Like a lock/unlock of the torque converter. The exhaust sounds different at that point too.

Ideas?

It may be that the TCC unlocked. The 75 MPH is the area that GM uses for the forced lock mph.

It may also be that the ECM went into DFCO. Upon lifting there is usually a delay before the ECM cuts the fuel off. Which may be enough time to coast down to 75 before DFCO comes into affect.

RBob.