86 TA originally came with computer controlled carb. I swapped the 305 for a 350 and removed the wiring harness to the computer. Everything is working great except the fan is not kicking on. I have checked and the fan connector is getting 12V with the key on and the engine hot, and no voltage when it is cooled back down. But for some reason, the fan is just not turning on. This is leading me to believe the fan motor is bad, but I just want to make sure that I'm not missing something and that unplugging the ECM shouldn't have an effect on the fan. It is just odd because the fan was working properly before, and I am getting voltage to the connector.

The fan did sit outside for a couple of weeks while I was doing the swap, I can't remember if it rained during that time. Could that have caused the motor to die on me? I did check and the fan itself is not seized up.

 

I don't have access to TunerPro or any BINs at the moment since I'm at work, but there's a decent chance that the fan is ECU controlled to some extent, like in a '92. I don't know for sure off the top of my head for an '86 305, but I do know that ECU fan control (on/off at certain temps/ speeds) was present on at least some thirdgens. If your motor has two coolant temp sensors (usually one in the head with a button connector for the gauge, and a 2 wire in the intake for the ECU), then the relay might just not be getting the signal to send power on to the fan. If this is the case, I believe it is possible to set up a separate trigger system for the fan with a switch that turns on/off at a specified temp without going through the ECU.... there oughta be some folks on here who've gone through the same thing before who can provide more details, but reckoned I could at least throw out a possibility as to why the fan won't kick on.

 

The fan relay is triggered by the ecm. There are 2 coolant temp sending units, one for the gauge, one for the ecm. Since you now don't need to tell the ecm anything, use that port to put in a sending unit to trigger the fan relay at the temperature you need.

 

So, to add a little context here. The car originally had 3 temp sending units. The one on the driver side head for the gauge, the one on the passenger side head for the fan, and the one on the thermostat housing which I assume went to the computer. I now have both the temp sending unit and the fan switch relocated to the intake due to fitment issues in the new heads. The third switch in the thermostat housing has been removed.

If I'm understanding correctly, I need to connect the fan switch directly to the relay? Sorry, I'm very much a noob when it comes to electrical and I am trying to learn.

 

Also, how could the fan connector be getting 12V if the relay is not being triggered, and how could the fan not kick on if it is getting power?

 

Oh interesting, hadn't heard of the 3 sensor setup... just did some digging and came across a thread from 2009, here. Posts #11 and #15 might help you out, turns out I was indeed barking up the wrong tree with the ECU. If you had the switches out at any point, there might be a chance that you accidentally swapped the two head sensors... they both use a similar blade connector, entirely possible that they just need to be swapped. I'm well into unfamiliar territory now though, so I'll let you check that thread out for yourself, guy was running into the same situation as you

 

Thanks for the link! I will check it out.

 

I thought curbed cars didn't use the ecm to trigger the fan? I thought that was just TPI cars.

if so, then it would use the fan switch in the passenger head to ground the circuit and activate the fan.


Yu could try grounding the wire to see if the fan comes on. It could be the location doesnt have a good ground, or the switch went bad?


Take the fan out and see if it works with 12v applied



.