Torque Converter Intermittent Lockup Problems

[WhatTheFehl]

Just as the title says. I'm sure the question has been asked before, but I couldn't find anything through the search feature. The issue is that sometimes the torque converter in my car locks up perfectly and functions just fine, then other times it doesn't lock up at all. Pulling up on the brake pedal doesn't have any effect. The transmission shifts perfectly otherwise. What could be the issue here? A failed sensor somewhere? I'm not sure.

It's a 1995 Grand Prix 4T60E

[slick]

Whats the engine temperature when it does and does not?

[WhatTheFehl]

I've never noticed any sort of pattern with engine temperature or anything to be completely honest.

[AL]

When I drove this car it was after we had been driving around for a good portion of the night and it was at operating temp and it still wouldn't lock up on the highway

[WhatTheFehl]

When I drove this car it was after we had been driving around for a good portion of the night and it was at operating temp and it still wouldn't lock up on the highway

Yes, but Friday night driving home from work it locked up perfectly on the highway the whole way.

[AL]

I was just answering slicks question

[WhatTheFehl]

I know, but I was reinforcing the randomness of the situation

[Galaxie500XL]

My '95 LQ1 Cutlass does the same thing once the trans temp rises above 180 degrees. Seems to be a common problem with the 4T60E, I believe it's related to either the PWM solenoid, or the TCC clutch solenoid, which are inside the transmission. A poster a few months ago reported success with cutting the lead at the transmission wires for the PWM solenoid, but myself, I'm planning a rebuild for the transmission before warm weather arrives.

[Brian P]

The PWM solenoid should not be confused with the TCC apply/release solenoid. The PWM in simplest terms acts as a fluid pressure (or flow) regulator to the torque converter clutch to soften the application of the TCC. The PWM solenoid has a very high failure rate during its early years of introduction in the W-line (1994-1997 or so). They tend to act up and cause slipping or lack of clutch activity when the transmission has been warm for a period of driving and eventually will fail altogether.

The PCM controls the ground circuit to this solenoid via "pulsations". You could try cutting the control wire, or if you want to be neat about it, pull the terminal out of the plug. This wire is located in pinout "C" of the transmission harness connector just above the vacuum modulator (under the airbox, front of tranny). The wire is "dark brown".

It's worth a shot if nothing else. With the PWM solenoid out of the equation, the application of the torque converter clutch will be abrupt but it should be consistent.

[Galaxie500XL]

True, but a bad PWM solenoid can lead to the symptom. The PCM monitors "slip" from the torque converter. If the PWM is too slow in allowing full hydraulic pressure for lockup (I think 3-5 seconds), the PCM will detect the excess slip, and disable further lockup attempts until the next start cycle.

[WhatTheFehl]

PWM = Pulse Width Modulation Solenoid? (ACDELCO Part # 2141861 on RockAuto)

I'm assuming that even though it is a fairly cheap part ($40), it is such a pain in the ass to replace that unless I'm planning a transmission rebuild it isn't worth the trouble?

[Galaxie500XL]

Well, starting in '95, the side cover was redesigned to allow a transmission mount to be attached...which means there's lots of fun to be had.

I figured my Cutlass has 207,000 miles on it, and the torque converter sounds like a coffee can full of rocks on takeoff, so I'm just going to rebuild the transmission.

[WhatTheFehl]

With any luck this engine/transmission combination won't be in there a whole lot longer (really want a 3500 and haven't decided on transmission), though I'm not sure how much longer it will be before the car will be promoted from DD to project. In the meantime, I sure wish I could have the few MPGs that I'm losing because of this back.

[Crazy K]

FOLLOW WOOL SMITHS ADVICE.

The difference you feel or see of having or not having a working PWM is minimal. SIMPLE. EASY. STRAIGHT FORWARD. DO ET!!! I've done this on three transmissions and never looked back.

you may also benefit from an auxiliary(external) transmission cooler... though saying that will bring someone like Bob out of the woodwork to argue.......

[Galaxie500XL]

X2 on the cooler...I added one from a 3.8 Regal to my '95 LQ1, the cost was minimal, and keeps the transmission temp down long enough for me to make my usual commute back and forth to work each day without encountering the lockup issue. On long trips, though, especially in summer, 30 miles is about as far as I can drive before the PCM disables the TCC.