So I have a 93 LX with 2.3L engine. I have replaced the following:
Thermostat
Temp Sensor
Water Pump
Radiator cap
Lower Rad Hose.
Car will get to operating temp when sitting at idle. But as soon as you start driving it drops to 130. If you drive more than 20 miles it will go into limp mode. Only code it shows is a code 21 (coolant temp out of range). Please help. Im baffled

 

https://www.stangnet.com/mustang-for...24-huh.525410/ a 1993 has limp mode?

The link above is to check your resitances at various operating temps. You should do this at two point. At the sensor connector and at the ECM pins. This will verify that the wiring itself is good and that there are no breaks, grounds or increased resistances from the sensor to the PCM that could be causing the issuing.

 

I assume limp mode because the car won't go over 15mph and if I get on the gas pedal it falls flat on its face and tries to backfire. Only code it shows is code 21. So I assumed it to be a type of "limp mode".

Thanks for the link I am going to check it out and see what kind of readings I get from the wires.

 

Did you run the code test while the engine was cold or did you idle or drive the vehicle for 10-15 minutes before you ran the test??If it was warm,the code is likely valid.If it was cold,I would clear the code out so you can run the test again.Make sure the engine is at operating temp before you run it this time.If the engines cold when you run the test,that itself will cause an ect code.If the code reappears,trouble shoot it using the link listed in post 2.You should know,however,that the ect sensor has nothing to do with your engine not reaching operating temp.The ect sensor is used by the ecu strictly for the purpose of controlling fuel & timing values,so it doesn't affect the temp gauge.You had mentioned replacing the temp sensor.Did you replace the ect sensor,cooling fan sensor or the coolant temp sender?? The diagrams below will show you each of the components locations,so you can verify the correct one was replaced.If the temp Sender is bad,it could be causing the gauge to read inaccurately.Youll normally experience hard starts,hot no starts,rough running or other driveability issues if the ect sensor is way out of range.Fuel consumption usually goes up too.I have seen brand new thermostats be faulty too,right out of the box.If the tstat is the correct temp rating and its working correctly and the cooling fan is only coming on when its supposed to,the coolant temp should run at a normal temp.Dont run a 180° tstat during the winter.The 192-195° oem tstat should really be used year round, especially in your 2.3 Have you popped the hood,when you first start the engine and once the engine reaches temp then drops back down to the lower temp you mentioned, to see if the cooling fan is running or not at these times?? If its running during those times/temps,the cooling fan switch or IRCM could be faulty & causing the cooler temps. The fan should most likely never need to be running during winter time while on the highway because the cold airflow through the radiator should be plenty enough to keep the coolant/engine at the correct temp.If the fan switch or ircm is faulty,it may be causing the cooling fan to run all the time,in which case, the coolant temp may be normal while idling or stopped,but once you're driving on the highway and the additional airflow is being forced through the radiator + the fan is also continuing to pull air through the radiator + air is also flowing over the engine from the increased speed also,you can see how quickly this could pull coolant temp way down or never let it reach operating temp to begin with.I would definitely make sure you replaced the correct sensor + check the fan to see if its coming on when it should not be + check the integrity of the new tstat.If theres a possibility the temp gauge just isnt reading correctly,you can check the gauge & wiring by pulling the wire off the sender,turn the key on then pull the rubber wire boot back enough to touch the metal portion of it directly to the block or cylinder head.The gauge should peg to the hottest or max point on the gauge.If it does,the gauge and wire are good so the sender could be bad.For the ect code,if the ect is bad,the ect sensor should be replaced. If you see that the fan is running constantly, disconnect the fan switch harness,shown in the diagram,and that should shut the fan off so you can then test drive it and see if temps go back to running at the correct temps.
The diagrams will verify which part youve replaced so far.

 

The only time I have got the fan to come on at all is when I unplug the coolant temp sensor I replaced. The sensor I replaced was in the heater core line right off the firewall. I haven't been able to locate any others. I will use the diagrams to find them. And I wondered if the thermostat was bad. I ordered a motorcraft one and just installed today. Burped system and got filled. Car ran for about 15 minutes and the gauge got up to about 150 160. Then once I started driving. It was back down to 130 within 1/4 mile. I drove it home about 17 miles and the heat was hot and the car ran great. The temp would try to rise a little when at a red light. Then back down to 130. Never got a check engine light. ( it comes on when it starts acting up then goes away after I start it back up.) I popped hood when I got home and all hoses plus radiator were very warm but not "hot" and when i twisted cap I had pressure releasing. So the new thermostat made slight change but the dash gauge is still not working. I am going to get an aftermarket gauge to hook up so I can see what the actual temp is. But before I do that I am going to check for those other sensors. Thank you so much for the detailed response!

 

I just took the diagram out and took a look. I don't have any sensors on the lower intake. Just the plug wires and injectors. Nothing around or in between.

 

Do you have the 2.3 with 8 spark plugs?? If yes,my apologies.I thought the 2.3 Mustang
had the 4 spark plug 2.3 I'll post new diagrams in the morning for the 2.3 with 8 plug configuration.They must have made the change to this 2.3 in 91-93?? Be back in the am with those diagrams.

 

Yes. My 2.3L has 8 plugs. I will check out the new diagrams and see what I can find. Thanks

 

Ok like I said previously,my apologies for the confusion.Im posting a new diagram & a previous diagram for the coolant temp sender (for the gauge) just in case you need it.However the sender is in the same location for both 2.3 engine types.After doing some research,it appears that your fan is indeed controlled by the temp reading from the ect sensor in your heater hose vs a fan switch. The ecu uses the ect reading for fuel & timing adjustments & also to indicate when the fan needs to be turned on/off.According to the Chiltons manual,a ect reading of 221° is the fan turn on temp & 200° is the fan turn off temp.The fan is also turned on when the ac is running and the vehicle is at/below a speed of 43mph and its turned off when the vehicle is at/above a speed of 48mph.So when the coolant temp reaches 221° & the ecu sees this signal from the ect sensor,the ecu then signals the ircm & it activates the fan.
Make sure you clear that ect code out by clearing the ecu kam (keep alive memory) This is done by disconnecting the neg battery cable for at least 5 minutes.If you fail to do this,the adaptive correction factor that was being used for the defective ect sensor,will be applied as the correction factor for the new sensor and driveability issues may occur down the road,even if nothing is wrong with the sensor.Long story short,adaptive factors are simply values the ecu uses for each sensor that compensates for its tolerance & wear as it ages.It allows the ecu to continue using the readings a out of range sensor is outputting,up to a certain point.So dont forget to do this if you haven't done so already.I'd say the ect sensor likely solved your issues,if the code & driveability issues are now gone.
I assume its cold where you're located,& if so,you can try placing some cardboard in front of the radiator to see if that helps the coolant temp increase somewhat since your problem seems to be occurring primarily once you're moving on the highway.The cardboard will block alot of the cold air hitting the radiator so maybe that'll help.
The cooler temp reading will increase fuel consumption somewhat,because the ecu richens the fuel mixture the cooler the ect reading is.
Do that sender wire and gauge check I mentioned to make sure they're both functioning correctly because its possible the temp sender may be acting up,causing the gauge to read the wrong temp??

 

Ok so I unhooked neg terminal. Waited 15 mins then hooked back up. Put cardboard in front of radiator. Drove it around 8 miles after letting idle for 10 mins. !Temp got up to around 145 while driving!. Im going to go for a longer drive momentarily and see what happens. Fingers crossed but I believe the ecm reset may have fixed it. Thank you so much!