I've had this car about 5 yrs now, and as far as I can tell, the fans have never came on on their own. If I turn the AC on they'll work, but ifthe AC isoff my car will go to about 240 degrees and sit. I have replaced the Coolant Sensor and the wire connector. I still don't have any fans. If I disconnect the sensor, the fans kick on and the engine runs like poo.

The SES light says Random Multiple Misfires Detected and Engine Temp is different than what is expected (or something close to that).

Details of my car: bone stock 1997 Conv. z28 6 spd w/ 160k miles. Tune-up performed 50-60k miles ago (New GM opti, MSD wires, NGK plugs, and coil). New O2 sensors, PCV valve, and oil changelast weekend. I think the waterpump may be leaking, and if so, this will be the 3rd one since I've owned the car.

Any help would be appreciated, because when I go to a mechanic they want tostart withthat opti-spark.

 

Well, if water is leaking on the optispark, it will eventually mess it up. Random multiple misfire is usually due to a lean running condition, a bad sensor, or a marginal ignition part that affects all cylinders, such as the coil, coil control module, or the Opti. Also check the cat conveters and EGR. A clogged converter and bad EGR may also cause misfires.

Disconnect the electrical connector & see how things run with the MAF disconnected. If it runs better then try cleaning or replacing the MAF. Check the fuel pressure and pressure regulator, and if OK throw a few cans of fuel injector cleaner in a full tank of gas and see how it runs after the tank is almost empty. Get a scanner and check all the sensor outputs and verify that they make sense, look at the O2 sensors and verify that they are cycling up & down rapidly. If all this checks out OK, check out the ignition system.

 

My main concern is my fan problem. I've had it as long as I've owned the car. I've done just about everything to fix the misfireproblem, and usually what I try works for a week or two (except for the tune-up which worked for about 3 months) and then it goes back to where it is now. The one item that has never changed would be my fan mystery. So, I'm hoping that if I can solve that problem it will take care of the misfire.

I'm going to replace my intake gasket this weekend andclean/inspect the EGR valve. I have cleaned the MAF and replaced the MAP sensor as well. I replaced the air inlet elbow and it came with a new IAT sensor. I have used gm parts exclusively. Every year I change the fuel filter and run fuel system cleaner (including the manifold).

Although my gauge has never gone into the red, would the higher coolant temps cause the excessive waterpump leakage/failures?3 pumps in 5 years?!

Thanks again

 

I suggest you leave the AC on all the time till you figure the fan problem out. Make sure the refrigerant pressure in the AC system is correct, use a AC pressure gage and with a scan tool compare it what the PCM sees from the AC pressure sensor. Use a scan tool & see what temperature the PCM is reading from the ECT sensor. At around 225 deg you should see the PCM command the fans ON.

To test the fan control circuit:
1) Disconnect the plug from the ECT.
2) With a multimeter on Ohm scale, check the Black wire to engine ground, should be 0-5 Ohm. If not, then there is a problem with continuity to the sensor ground inside the PCM, or there is a bad engine ground.
3) Turn key to ON
4) With multimeter on Volts, check the voltage between the Black & Yellow wires, should be 5 Volts. If not, then there is a continuity problem to the 5 Volt source inside the PCM.
5) If both wires test good, then short the Black & Yellow wires to each other with a jumper wire. This simulates a very high temp, and the PCM should command the fans ON. If the fans go on then you can assume that the ECT sensor has problems. If the fans stay off, you can assume that there is a problem with the PCM.

 

Thanks for the detailed info, Pete. My fans finally came on today, it seems I just needed to be a little patient with my last "fix". I guess replacing the wiring to the sensor was the key. It seems to be a little hotter than 225 when they come on, but I'll take it for now. The SES light is also off. Now, if it will just stay off for more than a week...