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



.

 

hmm, you may be right. The ecm may not have had the relay trigger in the earlier cars. My brain automatically thought of the efi ecms.

 

Yeah I'm pretty sure also that the carb ECM doesn't work the fan. Only the fan switch.

The fan connector "is getting 12V", if measured with a multimeter or the like, because the meter is looking at 12V through the relay coil, which is only a few k ohms. That's exactly what you should be seeing.

As said, ground the fan switch wire with the key on, and the relay should click, and the fan start running.

The 2 [mr_spock] sen-sores [/mr_spock] in the heads, neither of which is actually a "sen-sore", are the temp gauge sending unit, and the fan switch. The only "sen-sore" is the 2-pin one with a yellow and a black wire, that was originally in the water outlet. The other 2 have very different connectors from each other. The temp gauge one has the old-style "nail head" thing if it's still original, or maybe a blade if it's a replacement; the fan switch is a single-pin round Weatherpak.

 

Would the fan trigger wiring from temp switch to relay be a part of the ECU harness on CCC setups? If so he removed that...

Sofa is spot on. Before touching the coolant switch, test at the relay and then at the switch by providing ground to the trigger wire and see if fan activates while key on. If it does, then your switch was swapped accidently with gauge sender or has failed.

You can (and maybe should) order a switch with a lower activation temp that is close to whatever thermostat you are running. It is common for people to put lower temp thermostats in without changing the trigger temps of the fans (whether via tune on fuel injected setups or the switches on carb'd setups). Before I swapped from my old 2 speed fan to my brushless fan setup I had my EBL trigger low speed and then a 185*F switch activate high speed. Worked pretty well.

 

I had the same problem with my fan not working. I replaced the fan motor, but no avail. I replaced relays, didn't work. Gave up and just wired the fan to a switch inside the Camaro. When I see it go above 200 I switch it on. Works like a charm.

 

Until the one time it doesn't. Like, The Human forgets to do it. or perhaps, Another Human is driving the car for some reason, and maybe doesn't know about it, or know how to use it, or even realize that intervention is required, until sitting by the side of the road somewhere inconvenient (it's ALWAYS in an inconvenient place) with burst hoses and coolant spewing everywhere from an overheated engine.

In ANY control system, The Human is the weeeeeeeeekest link. ALWAYS. Any industrial engineer knows that, and avoids depending on The Human for ANYTHING in something like a production process, unless there's absolutely no other way. Systems like that should be designed to simply do their job and leave The Human out of it as much as possible. In the case of using a switch to turn on the fan, yeah, sure; Not a bad idea at all; go ahead and do that, as an "override" that allows The Human to turn it on if it wants to do so; butt make The System fully automatic so that it doesn't depend for survival on The Human.

 

It is 2026, there is absolutely zero reason to have to do this. Fan control is one of the most basic wiring schematics. We have limitless information available to us at our fingertips. Use it to learn how to properly repair the problem.