I changed water pump and thermostat on my '94 Z28. Both are working great. The only problem is idling at red lights, the engine starts to heat up but the fans don't come on. Once I get moving it cools back down. Could using teflon tape on the sending unit on the water pump (which I believe is the one for the PCM) be causing this problem?Or should I just assume the sending unit is bad or not getting good connection?

 

Electrically it should have no effect because the sensor does not rely on engine ground, but has a dedicated ground lead from the PCM. Unplug the connector from the ECT, and short the yellow and black wires going back to the PCM with a 150 Ohm resistor. This simulates a very hot engine and the fans should come on. (A dead short, instead of the resistor,will bring up the SES lite and confuse the issue)
(A) If no, there may be a problem with the fan control circuitry, or the fan motors. Check the wiring from the ECT to the PCM, the wiring from the PCM to the fan relays,the fan fuse, fan fusible link, fan motors.
(B) If yes, the sensor is bad.

 

Thank youfor the quick reply. The circuitry from the PCM to the motors is intact. Also, the motors work fine when wired up directly. I'll check from ECT to PCM. I appreciate the tip on the 150 ohm resistor.

 

id check the wiring, and then try running a relay switch into your dash to turn them on when you car gets hot.