Background: My car is a 1988 305 TBI VIN E with a single fan and no A/C. When I bought it I was told the fan relay had blown and there was a switch under the dash to turn on the fan. The switch was connected to two wires that ran through the firewall to the pigtail which was unplugged from the relay. As far as I can tell, when the switch is closed power flows from the battery across the fan to ground making the fan run. I'm trying to return the car to stock and remove this very poorly wired switch.

Problem: I replaced the relay and warmed the car up to just over 105C (221F) and the fan didn't come on.

What I've tested: I jumped A and B on the ALDL still no fan. I heard some ticking from under the hood but it wasn't from the fan. Next I checked the resistance on the temperature sensor, the car had cooled some since the drive and as such the resistance was 401 ohms which seems right when I compared it with the gauge. With the engine running I disconnected the coolant sensor and the CEL came on. I also checked the fuse under the dash

My conclusion: The fusible link, fuse, fan and sensor are all working fine. The ECM is aware of the sensor and is receiving input. So the sensor gets hot and it's resistance lowers, the ECM interprets this and based on it's settings (which I can't check) sends a low amperage signal to the relay to open allowing high amperage current to turn the fan.

My question: why doesn't the fan turn on? Is there a way to test the wiring from the relay to the ECM? have I missed something obvious?

 

on your tbi car the coolant temp sensor in the passenger side head grounds the relay coil at the specified temperature.

 

 

here is some napa part numbers if your switch is bad and you want to select a different on temp.


still haven't found an adequate fan switch. You might have to call up your local Napa to see if they have them.

MPE FS111SB On 245-Off 229

MPE FS112SB 229-Off 213

ECH FS111 On 220-Off 204

ECH FS112 On 229-Off 213

http://www.summitracing.com/parts/hyp-4028

http://www.summitracing.com/parts/hyp-4026

 

Okay cool, so if I wanted to test this I should unplug the sensor and jump the two wires or ground one of them?

 

just ground the wire going to the sensor ( single wire ) and the fan should come on.

 

to test the fan switch and relay turn your key to the accessory position and ground the temp sensor wire. If the fan goes on you have a bad sensor. If it doest go on start testing the power and ground on the fan relay.

 

I'm looking at the wrong sensor. I was looking at the one next to the thermostat housing that has two wires coming out of it. I think I see the one you're talking about on the passenger side low down on the block but I'll have to wait till morning to see it clearly. Cheers and thanks very much for the help