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-Fans not coming on at temp or with AC on ( ac system is empty)
-I Jump A/B on ALDL and Fans turn on
-I get 12v power at connector for Relays
-Both Fans turn on when directly powered
-When unplugging coolant temp sensor
both fans turn on and when plugging back in stays on even turned when turn car off and back on but after car sits for few min the fans are off again
I’ve changed CTS, both relays and had to repair engine harness both relays where rattling why I replaced
( Engine harness was fried and it also fried original ecm i repaired entire engine harness and replace ecm with used one but still using original prom )
this the last thing trying to figure out since getting her back up and running everything else is runs good
could it be bad prom from when ecm was damaged due to electrical issue that burn the wires ?
Last edited by Zach James; Apr 30, 2024 at 10:26 AM.
I can't say I've had your issue exactly, but when I bought my 84 the factory relay on my coolant fan was melted and the fan would not spin. I also replaced the relay with an aftermarket relay that had similar wiring and the fan still wouldnt spin. Same as you I connected direct power and the fan spun without a problem. What I ended up doing was buying one of those cheap relays on amazon and wiring it in. Now in my case I am controlling the coolant fan with my FiTech unit as I wired it in, in place of the temp sensor as most would wire in a toggle on switch in the dash. But it is capable as running as a standalone and will come on when the sensor hits it temp. you could also wire in a manual override as mentioned above. Just a thought that might get you by even as a temp solution for very little cost, I paid something like $20. Here is a picture:
-Fans not coming on at temp or with AC on ( ac system is empty)
-I Jump A/B on ALDL and Fans turn on
-I get 12v power at connector for Relays
-Both Fans turn on when directly powered
-When unplugging coolant temp sensor
both fans turn on and when plugging back in stays on even turned when turn car off and back on but after car sits for few min the fans are off again
I’ve changed CTS, both relays and had to repair engine harness both relays where rattling why I replaced
( Engine harness was fried and it also fried original ecm i repaired entire engine harness and replace ecm with used one but still using original prom )
this the last thing trying to figure out since getting her back up and running everything else is runs good
could it be bad prom from when ecm was damaged due to electrical issue that burn the wires ?
key on, ground temp sensor wire and fan should come on. at least it does on my 84. temp switch or wiring to temp switch could be bad. good luck
I can't say I've had your issue exactly, but when I bought my 84 the factory relay on my coolant fan was melted and the fan would not spin. I also replaced the relay with an aftermarket relay that had similar wiring and the fan still wouldnt spin. Same as you I connected direct power and the fan spun without a problem. What I ended up doing was buying one of those cheap relays on amazon and wiring it in. Now in my case I am controlling the coolant fan with my FiTech unit as I wired it in, in place of the temp sensor as most would wire in a toggle on switch in the dash. But it is capable as running as a standalone and will come on when the sensor hits it temp. you could also wire in a manual override as mentioned above. Just a thought that might get you by even as a temp solution for very little cost, I paid something like $20. Here is a picture:
interesting I’ll look into it was trying to get it running like stock as it should before anything but this might be easy solution
Normally, grounding the sensor wire closes the circuit to energize the fan relay. I tapped into the ground wire and ran it to a switch I placed under the dash so that I can turn on the fan anytime the engine is running. I just had to run a wire from the other side of the switch to a nearby ground. Too easy. That allows you to keep driving while you diagnose your sensor problem. Also, turning on the AC should turn on your fan.
Cooling fan diagnosing
