Intermittent TC Lock-up Problem

[DAVID C]

I have a problem with my stock (except for a tranny brake) 200r4 converter. Ocassionally (more often than not,) it cycles from locked to unlocked while at a steady cruise above 50 mph. I've checked all grounds behind the right side of the engine, cleaned them, and even added some at the ECM. I've taken apart the harness behind the mtor and checked for pinched wires... No luck. If I use my manual switch at the aldl port, it stays locked. Without using the manual switch, it will usually stay locked if I apply moderate throttle. The direct scan shows it going in and out. Could it be something inside the tranny like a weak solenoid, or pressure loss from a leaky valve body gasket? I think it started shortly after the t-brake install. It sounds electrical though. Some days its fine till I hammer it for a few seconds, then it starts cycleing. I've tried replacing most of the sensors, like the TPS, MAP, and VSS. I also notice the Direct scan shows the MPH bouncing around. This has been going on for over a year! Sorry for the long post. I'm trying to give as much info as possible. The tranny now has 144,000 miles on it but still seems fine otherwise. Thanks for any help you can offer. Dave C.

 

[MeanBuicks]

If your direct scan shows the TCC command going on and off and your manual switch keeps the TCC applied then the problem revolves around the ECM control. You did mention our VSS bouncing. That could have a lot to do with it. Does your speedometer work smoothly & properly?

 

[DAVID C]

The speedo seems to operate smoothly. I've also replaced the ECM. I may try to take another look at the speedo. Maybe it's loaded with dust bunnies. I think I have another speedo I could try also. Dave C.

 

[Russ Merritt]

You can also try holding the brake pedal up with your foot. The switch behind the pedal might need adjusting.

 

[DAVID C]

Thanks Russ. I've already tried that. I even replaced it. I'm fortunate to have two of these cars, so swapping parts is free. Dave C.

 

[Russ Merritt]

Gotta be the VSS then.