I have an 87 GN, and the T.C.C. "apply" is to early ... (B.T.W: the cars still bone-stock factory). I've learned that their is a pressure switch ( a 1 terminal switch ?), that one can update to "apply" the T.C.C at a higher rate of speed (say too about 45 MPH or so), instead of the 30 MPH apply that lugs the car down NOW , *(on a fully-warm engine while driving).

Can anyone please tell me where to get this "switch", and WHAT the "all-around" recommended apply range (or speed) is ?.

I have no issue NOW, just an "apply" that's way to soon (my opinion), and this dogs-down the engine until it's "thrown-out" / or I apply the brake slightly TO "throw it out".



Well-Known Member
Sounds like you are running a stock chip in the computer. Get rid of it and order one from Eric at Turbotweak. The stock chip locks the converter in 3rd gear depending on certain factors. You can order a chip from Eric which will not lock the converter until you are in 4th gear and he can program the chip to lock the converter at any speed you desire. His chips will also increase the drivability of the car.
Thank-you Mike !! "that's it" ? ... :unsure: *so it's very likely the "PROM" will (in my example) be a "one and done" task ?.

(IOW: I need not open - up the Trans. , or screw with ANYTHING in there ?).

Being I'm lucky enough to have someone so knowledgeable: WHAT SPEED you YOU recomm. ? *(for an apply) ... about 42 -45 MPH ?.

THX. again.


Staff member
does your ecm MPH match the dash MPH and is dash MPH correct and steady ?
ecm mph can be seen with a scan tool or scanmaster , both ecm and dash mph should be verified with a gps reading.
lockup should not occur until around 48mph even with stock chip , while you can get a 4th gear only lock chip and can get it with a higher mph thats just a bandaid , if yours is locking earlier either the ecm is getting wrong speed info possibly from wrong governer or drive gears in trans (trans may not be a BRF) or taller rear gears


Staff member
if you connect a scantool also verify that the 3rd and 4th pressure switches in trans are not on , those switches are NC type ( normally closed ) in the BRF trans and open under pressure to tell the ecm its in 3rd or 4th gear which enables the chip to command lockup . an ohm meter can also be used at to verify those switches are closed
a scan tool like power logger or directscan will show the flags

if your trans is not a brf none of what i sad applies as every other trans uses a different strategy of switches and wiring in regard to lockup



Staff member
if you look at wiring diagram youll see tcc is controlled by ecm by grounding pin A7 at ecm
if you run a switch on that wire you can prevent the ecm from locking through the chip
if you put a switch to pin F at ALDL and connect to ground you can force the lockup whenever wanted but you have to turn it off every time you come to a stop or it will engage in 2nd gear

if you unplug the four pin square connector at trans you will also prevent lockup (at all speeds) but at same time ecm wont know if you are in 3rd or 4th and besides lockup the trans flags are used by ecm to drop boost in 3rd if using the stock boost solenoid
:cow:Thanks to no end !. :)

I have a "TECH-1" Scanner, and I'll check it ... (the 3rd / 4th gear topic).

*Back at the time: *(and this was on my 1980 Regal with a 4.9 / 200C Trans.), there was a pressure switch that we'd exchange to "call-up" the converter (or RAISE the TCC "apply" speed) UP, from appx. 30 MPH, (TO SOON), to about 45 MPH. This evolved amid a Bulletin issued (back at that time), to STOP T.C.C "chuggle" / E.G.R surge ...

Anyway: The "THEN" old-style vacuum switch "saw" / or needed to see an "even vacuum" (or a vacuum of "X" / higher), to THEN got "lock-up" = problem solved.

Being ECM controlled (in this example), I just "THOUGHT" that a pressure switch was the cure-all HERE. The cars apart NOW, as I'm installing new Body bushings ... thus it cannot be driven.

Anyway: I'll check ALL THIS out. ;)