My cooling fans do not come on during normal operation. The fuse and relays are good. In traffic and at a stop, the temp will climb to 230+ with no fan operation. With air moving over the radiator while driving, the engine temp stays around 160. Turning on the A/C does not actuate the fans either. I can force the fans on by grounding the green and blue wires and the 5-6 DLC jumper trick turns them on too. Where do I go from here?

My LT1 is a '96 with OBD1 conversion. I just finished a Meziere water pump and 160 degree thermo install. The fan issue in question was evident after the mechanical pump failure, but before the electric pump install. I have gone through Shoebox's cooling system info and don't know what to do next. I have no scan tools at my disposal. I am pretty sure I have all the air out of the cooling system.

Thank,
Justin

 

It's possible that your coolant temperature sensor in the water pump is faulty. PCM uses data from the sensor to determine fan activation. You've proven that the relays and the wiring is good right?

 

Yes... relays and wiring are good.

 

You can test the sensor itself using an ohm-meter. Resistance when cold should be between 2,000 and 5,700 ohms, and slowly lower to 200 - 300 ohms as engine temperature stablilzes. Voltage at the sensor should also be 5 volts.

 

Yup, the water pump temp sensor send the signal to the PCM, so that could be bad. The sensor is only like $10, so it is worth a try...
You did just mess with the WP, so it is a possibility. But it could also be the head temperature sensor, which goes straight to the gauge. Another thing is that OBD II fans opperate differently than OBD Is. Have you looked into that?

 

Ok guys. I have some updated info. I just downloaded the free version of pcmcomm.exe from carputing.com. The temps from the PCM are pretty close to those on the gauge cluster. They're within about 10 degrees or so anyway. Also, when the A/C is on the program shows that fan 1 is activated. However, I'm pretty damn sure that it is NOT running. Does this rule out the temp sensors and if so what's next?

 

It's tough to troubleshoot without a scanner, but the temp sensor might be a good direction to go (as already suggested). There is testing info on my Tech Page.