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Discussion Starter · #1 ·
It seems that I remember reading there are two coolant temperature sensors on the 2nd generation one for the gauge and one that reports to the ECU for fuel mixture. Is this correct or did I somehow dream this up? The gauge is reading correct. I've looked on Rock Auto and can only find one ECT sensor. If there are two someone please tell me how to find the other one on Rock Auto. Something is definitely screwing up my gas mileage on the '94. I've replaced plugs/wires both of which it needed, PDFE sensor which I had a code for, cleaned the MAF sensor and located and repaired a vacuum leak yet the mileage is still low. This leads me to believe it's a problem with the ECT sensor or the O2 sensor. I have a brand new O2 sensor here at the house but can't seem to get anything on it where I can turn it to remove the old O2 sensor for the a/c lines.
 

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You are correct there are only the two coolant temp sensors; the one with two wires in the connector connects to the PCM and the one with a single wire to it drives the temp gauge. For unscrewing the O2 sensor I use a crowfoot wrench made by SK, It is a 13/16" 'flare nut' style wrench, and has the square hole for a 3/8" ratchet. I also normally take out the fan motor and shroud to make it easier to reach the O2 sensor. Tomorrow in the daylight I will get the SK number from my crowfoot wrench. Im already in my pajamas tonight.
 

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the socket I used was an SK 42228, and its 7/8", not 13/16", though the 13/16" size might also work. if you do a search for SK 42228 you can see what it looks like. Im sure lots of toolmakers have the same thing. I prefer the 6 point fractional flare nut, rather than the 12 point version. Most all 1of my sockets and wrenches are the 6 point kind.
 

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Discussion Starter · #4 ·
Thanks denisond3. Am I correct in assuming the coolant sensor that helps control a/f ratio is also the sensor that controls the cooling fan? I don't have any codes stored in the ECU. I ordered an ECT sensor from Rock Auto last night. Hopefully that will take care of my poor mileage issue.

I've got a regular 6 pt. O2 sensor socket and can get it on the sensor but then there's no room to turn the ratchet because the a/c lines are in the way. Right now I'm in the middle of a laminate flooring project that will probably take me the rest of this week then maybe I can get back to looking at the car.
 

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Yes, the temp sensor (with two wires to it) is how the PCM knows the adjust the a/f radio, and when the sensor is indicating the watertemp is about 205 degrees, it should turn on the low speed fan. If the water temp gets above about 215 degrees, the PCM turns on the high speed fan. But this depends on the relay inside the underhood fuse box, and the two relays inside the fender (behind the air filter housing and inlet horn) are working. And of course that the fan itself is okay. I have had a fan that burned out its front bearing.

Each summer on a hot day, I warm up the engine, then park it in the sun, with the engine idling. I keep an eye on the needle of the temp gauge, so I know how hot it is showing when the fan comes on. I watch till the temp gauge shows it is cooling down, and for the radiator fan to shut off - and to do it a second time.**
If your car has a working a.c. system, the PCM will turn the fan on its high speed whenever the a.c. is running. None of mine have a working a.c. system anymore though.
Of my five escorts, the temp gauges all show a different normal driving temp when cruising along, and a different point where the fan comes on during the annual test.
 

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Discussion Starter · #7 ·
You might also consider verifying that the temperature sensor in the airbox is functioning properly.
That's a good thought, I hadn't thought about the IAT sensor. If the ECT sensor doesn't do the trick I'll look into the IAT sensor. With gas hovering around $4.25 a gallon I need to find the problem.
 

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Discussion Starter · #8 ·
Hopefully I've found the problem. I was checking the resistance on the IAT sensor this afternoon and it showed it open. Sensor has been ordered and should be here Friday. Once I get the sensor in and have had a chance to check mileage I'll give an update.
 

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Discussion Starter · #9 ·
My last post was incorrect. Upon rechecking the IAT sensor it tested good. Apparently when I tested the other day I had the multi meter set at the wrong ohm setting. I had received the new IAT sensor today and was checking the ohm reading on it prior to installing it and decided to recheck the old one before putting the new one in and the readings were the same.
 
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