I have an '88 TPI Formula with dual fans and the only way I can get the primary to shut off is to unplug the relay. It is pretty annoying because the car really wont get up to operating temp anytime soon.

Here is what I've tried so far... I unplugged the relay and the 'trigger' wire from the ecm, this worked but obviously the fan would never turn back on. I have even unplugged the trigger wire AT the ecm to make sure the trigger wire is not crimped anywhere, and it seems to be fine. I have also tried a total of 3 different computers in the car with different chips in each one and still the same thing. The coolant temp sensor only reads about 150* during these tests, the guage agrees with the computer too.

I have unplugged the AC pressure switch and it still runs, then I put in a jumper across the plug with no results at all.

Any more ideas?

 

I have the SAME exact problem so right now its wired to a switch cause no one could help me, good luck with responses Ill be watching this thread too.

 

I forgot to say that it is the driver's side fan that is always on, that is the primary isn't it?

 

sounds like the ecm is being grounding by the connection that goes to the temp sensor unit in the front of the block/intake manifold.

 

ahhh i see that would be why changin the sensor didnt do anything for the problem oh yea and the driver side is the primary

 

I MAY have fixed my problem. I tried using a chip that has the A/C high pressure switch set to 'Normally Closed' instead of normally open. I thought this wouldn't work since my switch seemed to be normally open. But it seams to have done the trick.

Before I tried the chip, I ohmed the CTS at the computer and got about 1.5K ohms. When the harness is connected to the computer it goes to about 1.3K ohms. This was with the ignition off. With the ignition on the circuit seemed to have no resistance. I tried this a few times with no luck.

After the new chip the fans turned on at exactly 190*. I have the same temp set for when the A/C is on and off. I turned the car off and let it sit until the temp dropped to under 190* and the fan didn't turn on until it warmed up past 190* again.

Maybe I 'adjusted' something when I probed the computer harness, but I'm kinda happy now.