Code 21 – ECT sensor out of range. Broken or damaged wiring, bad ECT sensor.
Note that that if the outside air temp is below 50 degrees F that the test for the
ECT can be in error.
The ECT sensor has absolutely nothing to do with the temperature gauge. They are
different animals. The ECT sensor is normally located it the RH front of the engine in
the water feed tubes for the heater.
The ACT & ECT have the same thermistor, so the table values are the same
ACT & ECT test data:
Use Pin 46 on the computer for ground for both ECT & ACT to get most accurate
readings.
Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts
Pin 25 on the computer - ACT signal in. at 50 degrees F it should be 3.5 volts. It is
a good number if the ACT is mounted in the inlet airbox. If it is mounted in the lower
intake manifold, the voltage readings will be lower because of the heat transfer.
Voltages may be measured across the ECT/ACT by probing the connector from
the rear. A pair of safety pins may be helpful in doing this. Use care in doing it
so that you don't damage the wiring or connector.
Here's the table :
50 degrees F = 3.52 v
68 degrees F = 3.02 v
86 degrees F = 2.62 v
104 degrees F = 2.16 v
122 degrees F = 1.72 v
140 degrees F = 1.35 v
158 degrees F = 1.04 v
176 degrees F = .80 v
194 degrees F = .61
212 degrees F = .47 v
230 degrees F = .36 v
248 degrees F = .28 v
Ohms measures at the computer with the computer disconnected, or at the sensor with the sensor disconnected.
50 degrees F = 58.75 K ohms
68 degrees F = 37.30 K ohms
86 degrees F = 27.27 K ohms
104 degrees F = 16.15 K ohms
122 degrees F = 10.97 K ohms
140 degrees F = 7.60 K ohms
158 degrees F = 5.37 K ohms
176 degrees F = 3.84 K ohms
194 degrees F = 2.80 K ohms
212 degrees F = 2.07 K ohms
230 degrees F = 1.55 K ohms
248 degrees F = 1.18 k ohms
Diagram courtesy of Tmoss & Stang&2birds
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
(website host) for help on 88-95 wiring
http://www.veryuseful.com/mustang/tech/engine/
Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif
Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif
Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif
Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg
Codes 44 & 94 - AIR system inoperative - Air Injection. Check vacuum lines for leaks, &
cracks. Disconnect the big hose from smog pump: with the engine running you should feel air
output. Reconnect the smog pump hose & apply vacuum to the first vacuum controlled valve: Its
purpose is to either dump the pump's output to the atmosphere or pass it to the next valve. The
next vacuum controlled valve directs the air to either the cylinder heads when the engine is cold or
to the catalytic converter when the engine is warm. Disconnect the big hoses from the back side of
the vacuum controlled valve and start the engine. Apply vacuum to the valve and see if the airflow
changes from one hose to the next.
The two electrical controlled vacuum valves mounted on the rear of the passenger side wheelwell
turn the vacuum on & off under computer control. Check to see that both valves have +12 volts
on the red wire. Then ground the white/red wire and the first solenoid should open and pass
vacuum. Do the same thing to the light green/black wire on the second solenoid and it should open
and pass vacuum.
Remember that the computer does not source power for any actuator or relay, but provides the
ground necessary to complete the circuit. That means one side of the circuit will always be hot, and
the other side will go to ground or below 1 volt as the computer switches on that circuit.
The computer provides the ground to complete the circuit to power the solenoid valve that turns
the vacuum on or off. The computer is located under the passenger side kick panel. Remove the
kick panel & the cover over the computer wiring connector pins. Check Pin 38 Solenoid valve #1
that provides vacuum to the first Thermactor control valve for a switch from 12-14 volts to 1 volt
or less. Do the same with pin 32 solenoid valve #2 that provides vacuum to the second
Thermactor control valve. Starting the engine with the computer jumpered to self test mode will
cause all the actuators to toggle on and off. If after doing this and you see no switching of the
voltage on and off, you can start testing the wiring for shorts to ground and broken wiring. An Ohm
check to ground with the computer connector disconnected & the solenoid valves disconnected
should show open circuit between the pin 32 and ground and again on pin 38 and ground. In like
manner, there should be less than 1 ohm between pin 32 and solenoid valve #2 and pin 38 &
Solenoid valve #1.
If after checking the resistance of the wiring & you are sure that there are no wiring faults, start
looking at the solenoid valves. If you disconnect them, you can jumper power & ground to them to
verify operation. Power & ground supplied should turn on the vacuum flow, remove either one and
the vacuum should stop flowing.
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif
http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif
See
http://forums.stangnet.com/attachment.php?attachmentid=50636&d=1180923382 for a very nice drawing of the Thermactor Air System (smog pump) plumbing
If you have a catalytic converter H pipe, you need to fix these codes. If you don't, then don't worry about them
