Technical Question

[97 Zee]

I just replaced the Optispark and waterpump in my 97 Z28 78,000 miles. I thought I replaced everything correctly but when I took it for a ride and let it sit, the temp gauge went up past 210 (and they normally came on just past 210 on the guage) and the fans did't kick on. So I checked everything when I got home only to find out that I had the waterpump Temp sending unit wire switched with the Air temp sending unit in the flexable elbow that is hooked to the throttle body. There exactly the same except for one is black in color and one is gray. My question is.... Might I have messed up somthing in the ecu?? Because now that I switched them the fan still dosnt come on.

[Injuneer]

Now that you corrected the wiring problem, is it still going past 210degF? The low speed fans come on at 226degF? Is it getting that high? Remember, the dash gauge isn't necessarily all that accurate, and could easilly be 5-10degF off.

[97 Zee]

Yes it is still going past 210 and the fan is not comming on. If I remember correctly, The fan use to come on just past 210, what ever the actual temp. is I dont know. I guess I could just let it go to where there is no question ,on the guage, that it is past 226. and see if they come on. I'm pretty sure I'm there now tho. I guess I was mostly concerned that I might have done some real damage to the ecu. do you think with the wire swap that I did it might be possable. I'm hoping not.

[Injuneer]

You did not damage the ECU (PCM) by interchanging the coolant temp sensor (CLT) and inlet air temp sensor (IAT). Both those sensors are thermistors, with identical electrical characteristic (ohms vs. temp). You could switch them all day long, and not hurt the PCM.

But, the wrong data going to the PCM can cause problems. As a result of swapping the sensors, the PCM was thinking the engine was colder than it really was. Obviously is affects whether the fans turn on, but it also cause the engine to run in an enriched condition reserved for cold starts (depending on how cold the air temp was), and prevents the PCM from entering "closed loop" and correctly controlling the A/F ratio. I doubt any of this would have harmed anything.

First, make sure your fans still work. Turn on the A/C. Fans should come on. If they do not come on, and if they still do not come on after you verify the engine temp is over 226degF (this can only be done by looking at the PCM with a scanner), you need to start tracking down the power supply, looking at the fuses and the three fan relays in the electrical convenience box on the drivers fender, under the hood.