Cooling Fan comes on only with ECT disconneted

35th sc bird

Registered User
The fan comes when I disconnect the ect, I did check the resistance on the ect and it seems to be in line with what my Chilton book said it should be/ Any ideas from here why the fan is not coming on when the car reaches temperature? Thanks
 
When you say "reaches temperature", what temperature is it reaching?

And DON'T go by the gauge in the dash. It's a glorified idiot light, with sometimes no resemblence to the actual temp.

Plus, there's two TSBs on the sending units - one for the sending unit failing and reading LOW, one for it failing and reading HIGH, depending on the production date of the sending unit!

RwP
 
Keep in mind the factory setting for the EEC to turn on low speed fan is 220 degrees which is quite a bit up/over on the temp gauge. A suitable scan tool with coolant temp readout would come in handy to see what the temp actually is. Also if the cooling system was recently drained and refilled and not bled there could be a lot of air trapped in the system which could cause the two coolant sensors to see different temps. After a coolant change I've seen the gauge temp sensor read quite a bit hotter than the EEC temp sensor until air is replaced by coolant in the cooling system.
 
I've replaced ECT sensors for the same reason.. that is a "late" fan and of course, the results were essentially the same.. nothing was fixed. After scratching my head, I have rewired all of my SCs to have a 3 position switch (EEC/Manual Low/Manual Hi) on the dash that lets me turn on the fan directly when needed. I also wired in a tiny LED next to that switch that indicates that indeed the fan is running.

Anyways, the solution to the problem is to replace the EEC itself. What happens is the circuity on the EEC control card, degrades. You can study an EEC board schematic to see how this can occur. :confused:

The temp gauge on the dash works just fine BTW, as long as the contacts are clean and the sender (its a sender.. not a sensor!) is in good condition.
 
Anyways, the solution to the problem is to replace the EEC itself. What happens is the circuity on the EEC control card, degrades. You can study an EEC board schematic to see how this can occur.

It can occur but very unlikely, I've tuned hundreds of factory ford ecu's and I've never had an ECT input fail never, not a single one.

most likely the engine isn't getting up to temp for the fan to come on

I highly recommend getting a stock performance tuned chip to have the fans come on at a much lower temp, not to mention a chip can also be programmed to shut off the engine if it gets too hot to protect it from overheating
 
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