Morning!

I swapped an '86 MAF TPI system in to a CK5 blazer with a 700R4 transmission. Fresh engine, and the 700R4 was rebuilt. The ECM is 1227165 and I used a new Painless Wiring harness for the install. The wiring for the TCC with TPI seems straight forward yet I'm having some bizarre behavior at high speed. Here are the symptoms:

Transmission shifts fine through the gears and lockup functions as I expect it to in 3rd and 4th. Actuating the brake pedal disconnects the TCC as it's supposed to.
Everything is fine below around 60 MPH.

Above 60 MPH the TCC quickly locks and unlocks. It's not TCC shudder, it's definitely the clutch locking and unlocking very quick. Lock, unlock, lock, unlock about every quarter second. If I back off the throttle to around 5% it stays locked. When I apply throttle, say 10% or more it starts locking and unlocking quickly. It does this in 3rd and 4th gear. I'm using a custom prom based on ARAP, but the TCC tables are from AUJN.

I don't know why speed is a factor, but at lower speeds the TCC locks and stays locked as it's supposed to with light to moderate throttle.

I did some troubleshooting to try and rule out the brake switch. The CK5 originally came with cruise control and I'm re-using the normally closed brake switch from the cruise control wiring for TCC. Normally closed with no brake, and opens when brake is applied. The switch seems to operate as expected, but I did replace the connector ends to ensure good connectivity with the switch terminals. Here is another odd finding that I don't understand. Stock wiring shows fused 12V goes to the brake switch, then to the A terminal on the transmission, then to the lockup solenoid, out D terminal to the ECM. The ECM controls lockup by switching ground. If I remove the connector at the brake switch and test for voltage on the A terminal on the transmission, I show 12V on the meter. This sounds wrong to me as I've removed the only source of power to this circuit. If this circuit truly has power when disconnected from the brake switch, I wouldn't expect the brake switch to disconnect the TCC, yet it does. The transmission was wired by the rebuilder as 'Type 9' for the wiring.

For clarity if I remove the connector at the brake switch I have battery voltage at 420 purple wire and subsequently at ALDL terminal F. From what I've read the 1227165 ECM controls TCC by grounding A7 (tan/black). If this is the case, I would not expect to see battery voltage with the connector at the brake switch unplugged. Is my ECM kaput?

 

Check the lock/unlock versus TPS tables in the BIN. The 'to unlock' table values must be higher then the stay unlocked table values.

RBob.

 

Any resolve on this? Similar to mine, but mine is a 93 LT1.
My TCC loc/Unlock %TPS vs speed tables are OEM. See pic
My Constant table has unlock at 45 and lock at 55mp in low and high gears.

 

I used a manual toggle switch for my 700R4 back in the day, when I had a carb. Just one wire to the TCC and done.

Would be good in the mean time if the ECU isn't doing what it should be doing, while you figure that out at least you can drive / trust the car.