just installed a rebuilt quadrajet on my 87 caballero and cannot get the lock-up torque converter to engage. what could cause this?

The only connection between the carburetor and the transmission is the TV cable and that shouldn't cause the TCC to not lock up. Does the tranny shift through all of the gears OK? Do you shift into 4th gear? The ECM signal for the TCC solenoid doesn't come on until the tranny is in 4th gear. Is the "SES" light on?

:mrgreen:

There is one thing you might check if you are having problems with the lock up torque converter not locking, that is the temp sensor that is in the intake manifold. If it is not working properly it will not send a signal to the ECM and the ECM thinks the engine is still too cold to allow the converter to lock up. I had the same problem before I installed a 700R4. After changing the sensor the converter started working properly again. They are not expensive and easy to change. Good luck. Harald K.

That's true. It will also cause the ECM to stay in open loop. It's also possible that a defective TPS will prevent the TCC lockup.

The TCC will engage when:

1. Vehicle speed is above 24 mph
2. Engine is at normal operating temperature (above 70*C, 156*F)
3. Throttle position sensor output is not changing, indicating a steady road speed
4. Brake switch is closed

This is a good reason to have a scanner handy. All of these tests can be done with an inexpensive ALDL scanner.

:mrgreen:

Thanks for the tips. I'll check them out early next week. I do remember that several years ago, I had the tranny rebuilt and had the same problem the very day I left the tranny shop. I took it back the next day and the rebuilder took it on a test drive. He said the TPS was bad. I replaced it and the problem was solved. This time though, the TPS should not be bad with a brand new rebuild. Could it be that the TPS voltage is out of specs? Would that cause the problem?

Are you sure that the TPSwas replaced when the carb was rebuilt? The TPS signal should be about 0.5V at curb idle and up to 5.0V at WOT. If the TPS is bad you should get a code 21 or 22.

:mrgreen:

The SES light is not on, there are no error codes and I THINK the TPS was replaced during the rebuild. At least the TPS connector looks brand new. I have not set the TPS voltage yet. If the voltage is out of spec, will that cause the torque converter to fail to lockup?

So far, thanks to you all, I have the following list of potential causes.
1) Throttle Position Sensor bad/malfunctioning
2) TCC solenoid in tranny bad/malfunctioning
3) Temp sensor in intake manifold bad/malfunctioning
4) Brake light switch could be bad/malfunctioning

I do not own an ALDL scanner but have a friend who does. Will get access to it early next week.

Before I forget it, does anyone think a faulty O2 sensor could cause the ECM to fail to provide the signal for the converter to lockup?

...does anyone think a faulty O2 sensor could cause the ECM to fail to provide the signal for the converter to lockup?
No, it's not needed for the TCC lockup.

:mrgreen:

Thanks, Harlad K for the tip on the intake manifold temp. sensor. Today, I looked closely at the intake manifold and could not positively identify this sensor. I did see one in the coolant thermostat housing that appears to feed info. to the ECM. The coolant sensor that drives the temp gauge on the dash is located down on the block under the exhaust. Can you tell me where the sensor is located exactly and what does it look like? The engine is a 5.0 liter V-8.

Thanks in advance for your assistance.