borneobuzz

Hello, All! Please help, as I am at my wits end, and I know there are some smart folks out there. 1987 IROC-Z, 5.7 TPI, 700R4. (this is an engine swap...) Intermittent stalling while braking and turning(mostly downhill). Converter seems to be erratically locking/unlocking while braking as noted by voltmeter/ tach gage. Should my 4th Clutch switch be N.O. or N.C.? as mine is N.O. and book states "closed until 4th gear...". I have replaced TCC solenoid, and it did help with stalling, but still getting erratic locking while braking. Brake switch/ wiring good. Cut tan/black wire at ECM and drove around with VOM on computer and manual switch to ground. Trans seemed fine when I would manually ground while braking/ but computer operation was strange. I was getting 0 volts up until around 40 mph, then 13.8 volts above 40 mph, seemed to be consistent in operation. I am kind of stuck at this point and I feel that someone may have also experienced this and could provide some insight. I really appreciate your time in reading this and responding! Cheers!

W.E.G.

Braking draws vacuum in a power-brake system.

You are having transmission problems when braking.

My shallow understanding of the 700R4 tells me there is a vacuum switch that sends commands to the transmission.

Bad switch, or bad wiring of the switch. Bad ground on the transmission vacuum switch?

borneobuzz

No, no vacuum switch. It is either ECM or something in trans, and I am leaning toward trans. Three wire plug, purple =12v from brake switch, dark green= ECM 4th gear and tan/black= ECM ground.