Engine 1986 GT ECT question

Magnet86

5 Year Member
Jul 21, 2018
66
8
18
Hagerstown, MD
I checked the ECT on the car today and found 19100 ohms with the air temp about 91 F or so. I also checked the replacement I have, a new old stock sensor and it showed 19900 ohms. This seems close but one of my manuals lists ohms as closer to maybe 22000 or so. As they both were close to each other, I may be off on the reading- I had to guess what it should be between what is listed on the chart. Does this sound good? Its the original one and I've had some issues with idle and timing lately but should have them taken care of. New fan clutch, cooling system flush, new stat, adjusted the idle and checked timing plus new distributor stator and a relocated new TFI module. If the reading is good I'd rather not replace it as I'm sure coolant will gush out. I know I should drain it down but I'm getting tired of replacing coolant.
Thanks.
 
  • Sponsors (?)


Overheating although the new fan clutch seems to be doing its job. New stat and flushed cooling system also. I have about as much coolant in the system as possible, very close to what the 'do it yourself' maintenance guide says it will hold. I drove it today and it seemed fine but only went a few blocks. Plus its about 90 here so it did very well.
The last time I tried this on my third trip down the block with the goal of driving maybe ten to twenty blocks then back to the driveway, it hesitated as if the timing was too advanced. Not a good feeling. Made it back but not sure why that happened. I then swapped distributors even though both have new stators in them. I may have had the diz bolt not tight enough but that's hard to tell. I didn't swap the diz until a few days later.
Timing is good now and the TPS is adjusted within range. Just under 1 volt at closed throttle. Idle speed is just below the 720 to 750 range. Car has plenty of power and response. I think I just need to drive it more and get it back on the road.
 
Dump codes sticky

Look at the top of the 5.0 Tech forum where the sticky threads are posted. One of them is how to dump the computer codes. Codes may be present even if the CEL (Check Engine Light) isn’t on. You don’t need a code reader or scanner – all you need is a paper clip, or if your lady friend has a hair pin, that will do the job.
I highly suggest that you read it and follow the instructions to dump the codes. http://www.stangnet.com/mustang-forums/threads/how-to-pull-codes-from-eec4.889006/





Code 21 or 116 – ECT sensor out of range. Broken or damaged wiring, bad ECT sensor.

[color= blue]Revised 6-Apr-2017 to add diagrams and resistance check for ECT wiring.[/color]

Note that that if the outside air temp is below 50 degrees F that the test for the ECT can be in error. Warm the engine up until you get good hot air from the heater and then dump the codes again.

The computer Engine Coolant Temperature sensor has absolutely nothing to do with the temperature gauge. They are different animals. The ECT sensor is normally located it the passenger side front of the engine in the water feed tubes for the heater. It has two wires that connect by a weathertight plastic connector.

The water temperature sender for the temp gauge is located in the driver's side lower intake manifold. It has a single wire that connects by a push on connector on the temp sender.


If you have replaced the ECT sensor and are still having ECT like problem symptoms, check the ECT wiring .

Computer wiring harness connector, wire side
71316.gif


Computer wiring harness connector, computer side
88243.gif



See the graphic for the 10 pin connector circuit layout.
68512.jpg


Check the resistance of the green wire on the ECT connector to the green wire on pin 7 of the computer connector. You should see less that 1 Ω (ohm)

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

88-91_5.0_EEC_Wiring_Diagram.gif


94-95_5.0_EEC_Wiring_Diagram.gif
Wiring_Diagram.gif[/

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