My car is acting weird today. Drove it to work this morning and the torque converter kept unlocking when it shouldn't. If I held the gas steadily increasing speed, it would hold locked. As soon as I let back even the smallest amount off the gas, it would unlock, then lock and unlock again until I started gently accelerating and then it would hold locked. Checked it for codes before driving it home this afternoon and nothing showed up. I drove it home and it was doing the same thing, the slightest movement of the pedal caused it to unlock and then lock back up again. I got pissed at it and punched it a few times on a long stretch of road until it redlined at 5000. After that, the dang thing started acting normal again. I drove the rest of the way back to town without a problem. Then just before turning down the road to my house, at 37MPH, it did it one more time, so I know it still has a problem. It was acting up so bad this morning that I am going to hook a switch up to the ALDL to keep the converter locked up when it starts acting up again to keep from burning up my transmission.
My question is this. Could I have a bad TPS that is intermittently doing this or possibly a bad ECM? How can I troubleshoot this, there are no stored trouble codes at all and the engine is running great.

 

It's probably the switch for the lockup converter. It should be a big white plug on the side of the tranny. Try unplugging it and see if that helps. You should have a 700r4 which is not computer controlled so it shouldn't be kicking back any codes that I can think of. I know back around that time a ton of GM cars had that same issue. My buddy works for the dealership and told me to unplug mine on the one car I had that was having issues with it and I never had a problem with it again. Worth a shot. It's free and requires minimal work...

 

Will the converter lock up with this plug disconnected?

 

Well I drove it again tonight for about 40 mile interstate trip. It ran flawlessly the whole time. I didn't notice one time that the converter unlocked when it shouldn't have. Maybe giving it a little 'attitude adjustment' the other day fixed it! I am still hooking up a manual overide to lock up the converter through the ALDL this weekend for the next time it acts up to help me troubleshoot it. I would really like to have it work rather than just disconnect the lockup clutch with the way fuel prices are soaring these days. I need every mpg I can get.

 

Today it started acting up again real bad. I pulled over and hooked up my switch to the A anf F terminals of the ALDL and drove back home. It stops the car from going in and out of lockup now. It engages at second gear and holds lockup under all conditions. If I floor it the RPM's go up like it's unlocking, but cannot tell yet if it's just passing gear or really unlocking. What can I check now?

 

Ok after driving it some more I have determined that it possibly could be the transmission. With the lockup switch ON it will still slip a litle sometimes in 3rd. O/D seems fine. Could the bands be slipping or something?

 

There's no such thing... no "switch for the lockup converter". Seems like this same erroneous advice has been given before on some other matter, IIRC when somebody had a motor that either misfired or ran too lean, and the engine reacted unfavorably to the increased load of the locked converter. Wasn't the right thing to do then, isn't the right thing to do for this either. A properly wokring car will .... ummm.... work properly when completely assembled.

A "switch" is a set of contacts that operates when some condition or other is met. The TCC doesn't have that in the transmission. What the trans DOES have however, is a SOLENOID (an elctromagnet), which works a little hydraulic valve, which in turn sends fluid to the TCC when the solenoid is powered. The "switch" that works the solenoid, is a transistor ("driver") in the ECM.

The big white plug goes to the SOLENOID for the lockup converter however, and to the SWITCH that tells the ECM that the trans is in either 3rd or 4th (and therefore is eligible to be commanded into lockup by the ECM).

Unplugging that connector disables the TCC. Not the right thing to do.

Jumpering the ALDL terminals operates the TCC at all times. Also not the right thing to do.

Plug it back in and un-jump the ALDL. Fix the REAL problem.

Your TPS guess is amost certainly correct. Just replace it. Those go bad sometimes by being sort of intermittent; like a scratchy volume control in an old radio or something. That's exactly what the TPS is, is the same kind of electronic device as a volume control; except instead of taking a large audio signal and providing an output that's some fraction of that based on wehre it's set, it takes a 5VDC input and gives an output that's based on where it's set (where the throttle shaft is). They tend to get "scratchy" right where they spend the most time: either right at idle, or right around cruising.

Don't worry about what the trans acts like with the wire unplugged and/or the ALDL jumpered. It doesn't matter.

 

IIRC some rebuilt 700r4 had a ball added to the lockup oil control to manually (?) cause lockup at a peticular time (oil flow pressure).

When I rebuilt tranny for my 85 4x4 diesel, the rebuild manual said to install the ball. I didn't. I was running a manual bypass (old dimmer switch on kick panel), to the seat belt lite, and wired to the lockup.

This allowed me to unlock tcc when needed per load. I didn't like the throttle position switch because by the time it unlocked it down shifted. what a pita.

Rebuilders install them so the tcc always lock at some line pressure. Saves replacing a cooked tranny as limited cooling in unlock.

There is a guy on the drivetrain board that is way better than me about these critters. Try asking over there.

Also the 87/88 chip I have, the tcc will unlock everytime you decel (coast). Hard on tcc clutch.

The 86 chip doesn't, when it goes into decel, (built 700's do not have the rear override clutch, for freewheeling ), the engine compression brakes (really slows down with 10:1).

With crusie control, it is fast, slow, then repeat. level ground with little rolling hills are a real pita.