I am working on troubleshooting my car's torque convertor lockup function. It is a 1986 Trans Am with the 305 TPI engine and 700r4 transmission. I already have a very good understanding of what torque convertor lockup (TCC) is and the theory behind how the ECM commands it based on certain requirements such as engine coolant temperature (ECT), a steady throttle position (TPS), a certain speed (VSS), brake pedal not depressed, and in some cases a 4th gear pressure switch being activated.

Main Issue: Lockup engages always at 40 mph regardless of throttle position. (It shouldn't be locking up under heavy throttle but it does). Once engaged it will never disengage when throttle is applied. (it should). The only way to disengage TCC is by lightly applying the brake switch or go below 40 mph

I have used my Snap On MT2500 scanner to see that TCC is commanded always at 40 mph and that TCC gets grounded and that it does not disengage upon giving throttle like it should. I want to suspect this to be a TPS issue but I see the TPS volt range reads from .54 volts at idle up to 4.2 volts at WOT. There are not jumps or gaps in between.

I have dropped the transmission pan and checked my solenoid and valve, wiring looks good, and found in my case I do not have a 4th gear pressure switch.

I do not understand why my ECM is commanding lockup always above 40mph and not disengaging it at throttle. Any input would be much appreciated.

 

Check your Prom numbers againt the list of "bugged" early chips in '86.. Hopefully as simple as that..

https://www.thirdgen.org/forums/diy-...ml#post1347221

 

Adding a normally open 4th circuit pressure switch and wiring so the circuit is not completed without 4th gear could be helpful for part of the drivability problems.

 

Thanks for that info. I am currently running a new Hypertech Thermomaster chip (126002). Prior to this I was running the original PROM in which TCC would engage at 20 mph rather then 40 mph with the Hypertech. The Hypertech certainly helped the situation by delaying TCC but it is strange that it will never disengage until below that speed.

 

I certainly will research this idea. I definitely can see it helping the drivability issue. I thought it was strange I did not have one to begin with.

 

It puzzles me why the ECM commands lockup always above 40 MPH regardless of how heavy the throttle is and it will never unlock unless traveling below 40 mph. Was thinking this could be a TPS issue but as stated above the TPS voltage range looks good from .54 volts at idle to 4.20 volts at WOT, with no gaps or jumps in voltage in between. Another recent thought I had is possibly the TTC lockup drivers in the ECM be faulty? I can certainly source a replacement ECM to try but would like to hear from others first.

 

Googled that chip out of curiosity and saw this mid way down the page, Not sure if it's applicable to your issue or is some sort of bad info as I'm certainly no guru..

Manual Valve Body (GM 700R4 w/Reverse Pattern)


I had a similar issue with my '86 years ago and the 1228291 chip fixed it and made it into a whole 'nother car.. Might be worth trying another newer factory chip from a similar build before vats came out or have one burned. I added an adapter when the 9th start injector finally went fubar as they are now defunked.. https://tpiparts.net/inc/sdetail/1495 so I'm on the '89 code these days.

160 to me seems just to cold for engines, I had one of these same Hypertech chips for a 350 '87 Corvette long ago when they were all the rage, never did like it and went back to stock..

 

Aum 3236 seemed to somewhat fix tcc lockup
https://www.thirdgen.org/forums/diy-...um-8993-a.html
if you need a stock memcal or what to know tcc lockup settings lmk.
i have lots of memcals as well and can update the tune.
some years used different ac pressure switch settings so not a plug and play.

 

I looked at a old Hypertech 126002 86 305 thermomaster tcc lock is 41 unlock 40 in 3rd and 4th.
not spread out very much for mph.

 

That seems about the ball park of the hypertech memcal. I would ideally like lockup to engage somewhere over 55. I will PM you.

 

 

Thank you @Tuned Performance for creating my tune that resolved the lockup "issue" I was having described above. I would recommend his service to anyone who wants a custom tune fast!

 

Hey guys just came across this thread and i was wondering I have a 92 Z28 5.7 TPI and when driving it and coming to stop light it seems to down shift a bit firm like the RPM are a little high so i was wondering if the TCC lockup is not disengaging like it should would that cause that and would it mess with TPS causing it to idle a little high some times. And if so would replacing the chip in the ECM help.

 

If rpm is high clean iac might help

 

Well I'll check it but i replaced it about a year ago and the TPS as well