Hello,

I have a 88 TPI 5.0 with the dual fans.

I did some looking around these forums and have tested the following:

Both fan relays by the battery.

Wiring from the ECU to the Primary Fan, actually disconnected the ECU and shorted the pin to ground and the Primary Fan was operational.

I have also replace the ECU with a remanufactured unit from Autozone.

The issue is this - Secondary fan start at ~ 240deg F, but the primary one (drivers side) did not start. After I replace the ECU, both fans now start at ~ 240deg F.

I have checked the wiring on the drivers side sender unit, and it is ok.

I know the sensor on the passenger side is working, otherwise the Secondary fan would not operate. (unless the wiring had been modified)

I have a good reading on the dash gauge, appears to be ok. (based on when the secondary fan starts.)

This car is 98% orginal, I just bought it from the orginal owner. The wiring and all items appear stock. The vehicle has about 106k miles.

I am currently thinking maybe someone changed or modified the chip in the ECU?

I dont know, I am at a complete loss.

Any ideas?

Oh and yah.. I finally registered. Got tired of just lurking as a guest.

-Tom-

 

Look around in here and you will find all the info you need on cooling. It is a major issue for our cars. I recently posted the wiring diagrams for the cooling fans so if you do a search for my posts you should find it.
I believe the secondary fan will only turn on when ac is requested. So try that and see if that kicks on the fan, and yes the ecm only turns the fans on at I think its 130 or 140 like you said. Way too late in my opinion. But if you want to fix it, you have to learn how to program the ecm or get an aftermarket coolant temp switch.

Good Luck

 

I have looked at the site before I regestired. Been lurking around here for a few years.

Anyway, I have the service manual on the vehicle and already have the wiring diagrams.

My main questions was: Could someone actually set the ECU to operate the primary fan at a higher temperature?

I was not really clear on the OP.

I spoke with a friend at GM, and think I might have this thing resolved tomorrow. (its raining and I dont wrench unless its emergency in the wet)

Anywho, thanks for the reply.

-Tom-