Key On Engine Off (KOEO) Testing Procedures 
We have covered three separate methods of testing the EEC-IV so we will need to simplify our descriptions from here on.  Whether you are using the Check Engine light, a volt meter, or a Code Scanner we will simply refer to it as a "reader."  

During the KOEO test the EEC-IV will output codes twice during its display cycle.  For instance if a code 23 and 66 were present the EEC would display 23, 23, 66, 66.  The EEC will display codes in the following order: 

1. Fast codes - used at the factory and are not readable by most scanners.
2. KOEO codes - any codes generated during the KOEO test.  If everything checks out OK, you should receive a code 11.  These codes will be repeated twice.
3. Pause of 6 - 9 seconds.
4. Separator Pulse - this pulse signifies the end of the KOEO codes.
5. Pause of 6-9 seconds.
6. Continuous Memory Codes - any codes generated during continuous self-test will be displayed here.  If everything checks out OK, you should receive a code 11.  These codes will be repeated twice.

1. Make sure you have a paper and pencil ready so that you can write down any codes output by the KOEO test.
2. With your reader disconnected from the EEC-IV diagnostic port, start and run the engine until it is at normal operating temperature.
3. Shut the engine off and wait 10 seconds, then connect your reader.
4. With the engine off, and your reader connected, turn the ignition to "Run" but do not start the car.  Throughout this test do not depress the throttle!
5. You will hear a few clicks and whirrs from the engine bay as solenoids are activated and sensors are tested.  The reader will flash briefly as high speed codes are output by the EEC-IV.  These codes are read at the factory and are not intelligible to most scanners.  Ignore this flash.
6.  If everything checks out OK you should receive a code "11."  If not, the EEC-IV will display any errors it has received.  Record these code numbers.
7. After a 6 to 9 second pause your reader should flash once, this is a separator pulse to let you know that no more KOEO codes are present.
8. After another 6 to 9 second pause your reader will begin receiving Continuous Memory Codes.  If no Continuous Memory Codes are present, you should receive a code "11."  If Continuous Memory Codes are present, your EEC-IV will display each code twice.  Record these numbers.
9. When all codes have been downloaded turn the ignition to "OFF."
10. If you wish to perform the test again simply wait ten seconds and then go to step four.
11. Check your code readings here and correct any problems, then re-run the KOEO test before continuing on to the KOER test.

Key On Engine Running (KOER) Testing Procedures 
After you have corrected any problems in the KOEO test you are now ready to perform the KOER EEC-IV test.  This test checks all sensors and engine functions while they are in their normal operating states.  This test requires up to three inputs from the driver during the test.  The first input requires that the brake pedal be depressed, the second requires that the steering wheel be turned at least one-half turn and then released.  Finally on cars equipped with an E40D automatic transmission, the Overdrive Cancel Switch (OCS) must be deactivated, then reactivated. 

As with the KOEO test, the KOER test will output codes twice during its display cycle.  The EEC will display codes in the following order: 

1. Engine Running I.D. Pulse - this pulse is used to identify the type of engine.  The EEC-IV will pulse half the number of cylinders.  For example, on a 5.0 Liter Mustang the EEC-IV will pulse four times, on a 2.3 Liter Mustang it will pulse two times.
2. Pause of 6 to 20 seconds
3. Dynamic Response Test - this is a single pulse that indicates that you should briefly move the throttle to Wide Open Throttle (WOT).  This test checks to verify the functinality of the Throttle Position (TP), Mass Air Flow (MAF), and Manifold Air Pressure (MAP) sensors.
4. Pause of 4 to 15 seconds during this time Fast Codes will be displayed.
5. KOER codes - any codes generated during the KOER test.  If everything checks out OK, you should receive a code 11.  These codes will be repeated twice.
6. KOER codes- if you press the throttle to WOT briefly the EEC-IV will begin a cylinder balance test.  When the test has completed its first cycle it will display result codes.  The test will continue to cycle at twice the threshold of the previous test until the engine is shut off. 

1. Make sure you have a paper and pencil ready so that you can write down any codes output by the KOEO test.
2. With your reader disconnected from the EEC-IV diagnostic port, start and run the engine at 2,000 RPM for two minutes.  This will bring the Heated Exhaust Gas Oxygen sensor to its normal operating temperature.
3. Shut the engine off and wait 10 seconds, then connect your reader.
4. Connect your reader, and start the car.  Don't depress the throttle unless you receive a Dynamic Response Code.
5. Your reader will flash your Engine ID Code, if you have a 5.0 Liter Mustang this will be four flashes.  Immediately after you see the Engine ID Code depress the brake pedal, turn the steering wheel at least 1/2 turn, and for E4OD Automatic Transmission cars cycle the Overdrive Cancel Switch.
6. After a pause of 6 to 20 seconds you may receive a Dynamic Response Code.  This will be a single pulse on your reader that indicates the EEC-IV is requesting a WOT input from you. If you detect this code, briefly depress the throttle to WOT.  Failure to do so will generate an error code.
7.  After a pause of about 4 to 15 seconds, and if everything checks out OK, you should receive a code "11."  If not, the EEC-IV will display any errors it has received, they will be displayed twice.  Record these code numbers.
8. Check your code readings here and correct any problems, then re-run the KOER test before continuing on.
9. Once you have completed the KOER test you may shut off the ignition or continue on with the Cylinder Balance test.