Hi everyone!

After 10 months of work (interior, engine...), I was able to restart my 86. Everything seems to be working.

However, I haven’t had a TCC lock since the restart... Before, everything worked.

I made a modification to the wiring of the TCC, but I have a mode that allows you to switch to the original mode.

Original wiring diagram :



Modified wiring diagram : this allows either to drive in original mode, or with the TCC disconnected, or with the TTC activated with an preset engine vacuum (as an additional condition).



I checked the voltage, all is allright.
I do have a 12v output from the TCC pedal switch (purple wire), when needed. I added a LED (with resistance) betwenn this wire and F pin from ALDL.

BUT :
No TCC, no LED.
I checked the LED, I put the LED to the ground, it lights up. So I do have 12V again, with the purple wire of the brake pedal.

I think I've a problem with F pin.

Yet, the ECM seems to change state beyond 67km/h (42mph).
From this speed onwards:
- the voltage between F and ground changes from 12v to 0V
- The resistance between F and ground changes to 180 ohms. Is this normal?
I would have been inclined to think that F = mass (that is, less than 1 ohm) above this speed?

I worked on the engine intake. Did I forget to connect something?
I unplugged and replugged the ECM during my months of work (battery disconnected).

While driving, I connected F to A (on the ALDL), nothing happened either, I thought the TCC would have been forced, but no.

Does anyone have an idea ?
Does F become a continuity with ground when the speed exceeds 67km/h ?

Thank you

 

Tonight, I checked some things, and I realized that the TCC switch at the brake pedal no longer has continuity.

I presume it was the problem.
I took it apart, cleaned it because it was oxidized, and slightly tightened the contacts for better support, and checked that everything was flowing perfectly. It has regained its function !
Just more than to be tested at the next trip.















On the other hand, with this connector disconnected and ignition ON, I do have some 12V as input (pink striped black wire no. 39) : okay.
But I also have 12V on the output wire (purple wire no. 420), and that I don’t understand ?

 

Are you sure that is the the TCC switch in your fingers? The vacuum portion is for Cruise Control. The connector with pnk/blk and purple wires is the TCC. These wires may be on the brake light switch which has (2) connectors. K34 Cruise Control adds a second switch on the brake pedal, and some of the connectors move around. I forget if the TCC moves to the vacuum switch; use the wire colors (pnk/blk and pur) to confirm.

Also: You have your 'manual controls' in the 12V side of the circuit. The TCC is still only activated when the ECM is commanding TCC ON. If you want your control to work the way you describe, put the relay and switch in the tan/wht ECM side of the solenoid. Never mind: I re-read your intent: You want an "additional condition" of manifold vacuum. Not full-manual control regardless of ECM state.

 

Thank you IHBD for your comment.
It is indeed the TCC switch, coupled with the cruise control depression. The wires are indeed pink/black, and purple.

I tested the Corvette, the system works perfectly now.