I've been having some trouble with the TCC locking up too early causing poor response under light throttle, and surging with cruise control at low speeds.

I've just made an ALDL cable and done some datalogging with WinALDL... in the log, the lowest speed the TCC lockup flag came on is 21mph (34kph), which is just crazy. (Although, I haven't felt the TCC engage that early, only really around/above 32mph). See this post for a copy of the datalog.

I compared the speed sensor readings with the speedo and the ECM isn't getting the wrong speed, so it's not the VSS buffer.

What's the stock minimum speed meant to be for TCC lockup? (1227165) Is it time for a new ECM?

Thanks,
Stu

 

Most likely you need a new switch. It's actually common for the switch to go bad and give false pressure readings and enguage the TCL. I doubt its ECM related most likely the switch it just starting to go bad and this is the first sign.

 

I think it varies by year and application. My 86 T/A with 305 TPI would lock up the converter almost the instant it hit 2nd gear at normal part throttle acceleration. I mean it would lug it down to 1400 RPMs as soon as it upshifted out of first. Being as this car was totally dead-nuts stock with low miles and only being 5 years old at the time, I quickly accepted this as "normal," although I never did like it much. Seemed to lug the engine on the very bottom end of where it was capable of pulling smoothly.

21 MPH sounds about right, from decades-old foggy memory.

 

Well it never used to lock up that early... it started doing it a few weeks ago, and it's really annoying....

SSC... what switch are you talking about?


Cheers,
Stu

 

It does sound like a flakey switch.

Specially since u said it never used to do it, or did u not notice it?

The stock lockup tables suck it lol

First thing I change in any bin I do.

later
Jeremy

 

No, it DEFINITELY didn't do it before.

Is the switch you're referring to the 4th gear pressure switch? Looking at my datalog (take a look in the other post), "MCUIO:Overdrive Request" isn't consistent with when the car was actually in 4th, and "MW2:Overdrive On" is always 0. *shrug*


Stu

 

TCC Unlock to Lock - 28 MPH

TCC Lock to Unlock - 27 MPH

Bump those up to the low 40's when you reprogram.

Some time during the '87 model year those were rectified.

 

TCC switch. It's internal and all the wires that attach the the various switches on the valve body attach to it.

 

Actually, I probably also should have mentioned that I followed the TCC diags procedure in the GM service manual...


Ie:
- Ign on, engine off
- Test light between ALDL F and ground - light ON
- Apply brake, light OFF
- Release brake, short ALDL A & B - light should go off, but it only dimmed (about half brightness). Volt meter showed about 7 volts.

According to the manual, if the light doesn't go out, it's either "open CKT 422 or faulty ECM"

Anyone?