Dan88GTA

Hello everyone. I just bought a 1987 IROC since my 88 GTA was dying on me. I'm still trying to get all the bugs worked out of the new car. When I bought it, both of the cooling fans were running all the time. I've done many searches on this board, and have found a lot of information, but still have not been able to solve this problem. The first thing I did was unplug the secondary fan from the sensor on the passengers side of the engine. The secondary fan stopped running with that unplugged. Right now, it's cold enough out where running with the secondary fan unplugged is not a problem. I'm guessing it's a bad temperature sensor which I will replace when it gets a little warmer out. If not, I will just wire that fan up to a switch. Right now, I am more concerned with fixing the primary fan since that one is still running all the time. I replaced the relay, which did nothing to fix the problem. I have also tried to trace back some of the wiring, but it does not look like it has been modified in any way. I'm not sure what else the problem could be here. Temperature sensor? ECM? I unplugged the temperature sensor on the intake manifold and the fan continued to run.
Here is my other question: I understand that the primary fan is controlled by the ECM. Will it hurt the ECM if I rewire the fan so it bypasses the ECM? I am thinking of wiring it up similar to the way the secondary fan is wired. In this case, I would put in a Jet fan switch, or similar fan switch and then wire the relay so that the black wire with red stripe goes to the fan, orange wire is power from the battery, tan with white stripe is power from the ingition, and green goes to the fan switch instead of the ECM. Is there any problem with this set up? I appologize for the long post. Thanks for your advice!

Danno

First thing is, do you have a SES light on? You say there a few bugs, if the SES is on the primary fan will run all the time. Second, there is a pressure sw in the AC system that is normally closed. If it's unplugged or defective the pri fan will run. If you unplug the CTS it will throw a code and the fan will come on so that test is self defeating. You can measure the resistance of the CTS with an ohmmeter. The values are posted here. You can wire around the ECM, however the aux fan sw comes on at a higher temp so you will need a different sw as you said. I don't like modifying the system. Running both fans all the time places a lot of load on the generator and will cause premature failure as well as the fan motors. Regardless of what you read the factory way is the best.

Lo-tec

Welcome to the boards. I believe this is the primary fan, but doesn't matter. The switch or the relay for this fan is bad, and it's easy to test for it. With the engine cold, test the switch in the pass head for continuity to ground. If it is grounded when cold, the switch is bad. I would replace it with a lower temp one. If not, it's probably the relay. You should be able to find a pinout for the relay on the board. You can wire in a manual overide switch easily also. Get an on/off switch, and wire one end into the lead to the switch, the other to ground. Grounding the relay completes the circuit.

Dan88GTA

No, the SES light is not on. I had read about the switch in the AC system, but in many I my searches I found that this was only for 88 and above. Would an 87 have this as well? If I do wire around the ECM, I will definitely be using a different fan switch. I do not like modifying the system either and would rather keep the thing stock. However, I am really not sure what else to do to solve this problem. Everytime I think I have it figured out, the fan continues to run.

Lo-tec

I found this:

http://members.rennlist.com/3liter6/cool8dual.pdf

and this with a wiring diagram:

https://www.thirdgen.org/techbb2/sho...WIRING+DIAGRAM

I would check both relays to see if they are OK, and work backwards from there to see if something else is turning them on (bad switch, etc).

Dan88GTA

That's the wiring diagram I have been using to try and find this problem. I have read the article about fan control as well. Both of the relays have just been replaced. Since the wiring looks ok, it leads me to believe that it's either the ECM or the temperature sensor. I think I may just wire it to bypass the ECM. That would solve my problem for now, and would be very easy to put back to stock if I figure out what is going on.

Lo-tec

Did you verify if the switch in the cyl head was bad? If you were to fix that fan so it operated correctly, you could use it as the primary (with an aftermarket lower temp switch) and setup a manual switch for the other one until you figure it out (or just disconnect it). If you're not using your A/C, you really don't even need 2 fans.

Dan88GTA

I thought the switch in the cylinder head was bad, but that was before I noticed that the secondary fan relay had been smashed and then taped back together. I have to wonder what people are thinking sometimes. I replaced the relay, and I will test the switch again this weekend. But what you said was exactly what I was thinking. I am planning on getting an aftermarket switch (on at 200 and off at 185) and using that fan as the primary. The other fan I will either hook up to a switch, or I will tie both fans together so they will both turn on and off from that switch. I started up my old 88 GTA last weekend to see how the fans worked. When the temperature got up to about 220, both of the fans switched on together. I never modified it in any way, so I can only assume that it worked that way during all the years I drove it. Maybe a previous owner tied the two fans together. No matter what, I never had any cooling or overheating problems with that car. It always ran at just under 220.