Ford Mid-Size Cars 1971-1985 Repair Guide

EEC-IV System



One part of the Powertrain Control Module (PCM) is devoted to monitoring both input and output functions within the system. This ability forms the core of the self-diagnostic system. If a problem is detected within a circuit, the controller will recognize the fault, assign it an identification code, and store the code in a memory section. The stored code(s) may then be retrieved during diagnosis.

The EEC-IV system is capable of storing both ongoing "hard'' and intermittent "soft'' faults. As a result, it is possible to monitor irregularities which may not be immediately present.

While the EEC-IV system is capable of recognizing many internal faults, certain faults will not be recognized. Because the computer system reads only electrical signals, it cannot sense or react to mechanical or vacuum faults affecting engine operation. Some of these faults may affect another component which will set a code. For example, the PCM monitors the output signal to the fuel injectors, but cannot detect a partially clogged injector. As long as the output driver responds correctly, the computer will read the system as functioning correctly. However, the improper flow of fuel may result in a lean mixture. This would, in turn, be detected by the oxygen sensor and noticed as a constantly lean signal by the PCM. Once the signal falls outside the pre-programmed limits, the engine control assembly would notice the fault and set an identification code.

Additionally, the EEC-IV system employs adaptive fuel logic. This process is used to compensate for normal wear and variability within the fuel system. Once the engine enters steady-state operation, the engine control assembly watches the oxygen sensor signal for a bias or tendency to run slightly rich or lean. If such a bias is detected, the adaptive logic corrects the fuel delivery to bring the air/fuel mixture towards a 14.7: 1 or "centered'' ratio. This compensating shift is stored in a non-volatile memory which is retained by battery power even with the ignition switched OFF . The correction factor is then available the next time the vehicle is operated.

If the negative battery cable is disconnected for longer than 5 minutes, the adaptive fuel factor will be lost. After repair, it will be necessary to drive the car at least 10 miles to allow the processor to relearn the correct factors. If possible, the driving period should include steady-throttle open road driving. During the drive, the vehicle may exhibit driveability symptoms not noticed before. These symptoms should clear as the PCM computes the correction factor. The PCM will also store Code "19'' indicating loss of power to the controller.

Failure Mode Effects Management (FMEM)

The engine controller assembly contains back-up programs which allow the engine to operate if a sensor signal is lost. If a sensor's input is seen to be out of range-either high or low-the FMEM program is used. The processor substitutes a fixed value for the missing sensor signal. The engine will continue to operate, although performance and driveability may be noticeably reduced. This function of the controller is sometimes referred to as the limp-in or fail-safe mode. If the missing sensor signal is restored, the FMEM system immediately returns the system to normal operation.

Hardware Limited Operation Strategy (HLOS)

This mode is only used if the microprocessor fails to operate, or if the fault is too extreme for the FMEM circuit to handle. In this mode, the processor has ceased all computation and control, and the entire system is run on fixed values. The vehicle may be operated, but performance and driveability will be greatly reduced. The fixed or default settings provide minimal calibration, allowing the vehicle to be carefully driven in for service.


Hand-Held Scan Tools

Although stored codes may be read using a suitable analog voltmeter, the use of a hand-held scan tool, such as Ford's Self-Test Automatic Readout (STAR) tester or the second generation SUPER STAR tester, or equivalent, is highly recommended. There are many manufacturers of such tools, but the purchaser must be certain that the tool is appropriate for the intended use.

Both the STAR and SUPER STAR testers are designed to communicate directly with the EEC-IV system and interpret the electrical signals. The scan tool allows any stored faults to be read from the engine controller memory. Use of the scan tool provides additional data during troubleshooting, but does not eliminate the use of the charts. The scan tool makes information collection easier, but the data must still be correctly interpreted by an operator familiar with the system.

Other Diagnostic Tools

See Figure 1

The most commonly required electrical diagnostic tool is the digital multimeter, allowing voltage, ohms (resistance) and amperage to be read by one instrument. Many of the diagnostic charts require the use of a voltmeter or ohmmeter during diagnosis.

The multimeter must be a high impedance unit, with 10 megohms of impedance in the voltmeter. This type of meter will not place an additional load on the circuit it is testing; this is extremely important in low voltage circuits. The multimeter must be of high quality in all respects. It should be handled carefully and protected from impact or damage. Replace the batteries frequently in the unit.

Additionally, an analog (needle type) voltmeter may be used to read stored fault codes if the STAR tester is not available. The codes are transmitted as visible needle sweeps on the face of the instrument.

Although code retrieval does not require additional equipment, diagnostic procedures such as pinpoint testing will be easier with a "breakout box'' (a device which connects into the EEC-IV harness and contains testing ports for the dozens of wires in the harness). Direct testing of the harness connectors at the terminals or by backprobing is not recommended; damage to the wiring and terminals is almost certain to occur.

Other necessary tools for testing/troubleshooting include a quality tachometer with inductive (clip-on) pickup, a fuel pressure gauge with system adapters and a vacuum gauge with an auxiliary source of vacuum.

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Fig. Fig. 1: Breakout Box


Diagnosis of a driveability problem requires attention to detail and following the diagnostic procedures in the correct order. Resist the temptation to begin extensive testing before completing the preliminary diagnostic steps. The preliminary or visual inspection must be completed in detail before diagnosis begins. In many cases, this will shorten diagnostic time and often cure the problem without electronic testing.

Visual Inspection

This is possibly the most critical step of diagnosis. A detailed examination of all connectors, wiring and vacuum hoses can often lead to a repair without further diagnosis. Performance of this step relies on the skill of the person performing it; a careful inspector will check the undersides of hoses as well as the integrity of hard-to-reach hoses blocked by the air cleaner or other components. Wiring should be checked carefully for any sign of strain, burning, crimping or terminal pull-out from a connector.

You should always check connectors at components or in harnesses as required. Pushing them together will usually reveal a loose fit. Pay particular attention to ground circuits, making sure they are not loose or corroded. Remember to inspect connectors and hose fittings at components not mounted on the engine, such as the evaporative canister or relays mounted on the fender aprons. Any component or wiring in the vicinity of a fluid leak or spillage should be given extra attention during inspection.

Additionally, inspect maintenance items such as belt condition and tension, battery charge and condition, and the radiator cap carefully. Any of these simple items may affect the system enough to set a fault.

Reading Codes

See Figures 2 and 3


A hand-held scan tool, such as the STAR or SUPER STAR tester, may be used to retrieve stored fault codes. Simply connect the tester's service connectors to the vehicle's Self-Test connectors.

Follow the directions given later in this section under Quick Test Procedures for performing the KOEO and KOER tests. Be sure to release the tester's push button, if applicable, before beginning the Self-Test.

Digital codes, such as "23'' will be output and displayed as numbers on the hand-held scan tool. (The codes may also be read using an analog voltmeter. For further details on this alternative method, please refer to the following portion of this section.)

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Fig. Fig. 2: STAR tester displays. Note that the colon (: ) must be present before codes can be received

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Fig. Fig. 3: STAR tester and analog voltmeter hook-ups-EEC-IV system


See Figure 4

In the absence of a scan tool, an analog voltmeter may be used to retrieve stored fault codes. Set the meter range to read 0-15 volts DC. Connect the positive (+) lead of the meter to the positive battery terminal and connect the negative (-) lead of the meter to the self-test output pin of the diagnostic connector.

Follow the directions for performing the KOEO and KOER tests. To activate the tests, use a jumper wire to connect the signal return pin on the diagnostic connector to the self-test input connector. The self-test input line is the separate wire and connector with or near the diagnostic connector.

The codes will be transmitted as groups of needle sweeps, whose cadence corresponds to the codes' numerical representation. Please refer to the accompanying illustration for details on counting the needle sweeps in order to determine the transmitted code. Continuous Memory (intermittent fault) codes, if present, are separated from the KOEO codes by a 6-second delay, a single sweep and another 6-second delay.

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Fig. Fig. 4: Code display patterns on an analog voltmeter


Quick Test Procedures

The EEC-IV system may be interrogated for stored codes using the Quick Test Procedures. These tests will reveal "on-demand'' faults immediately present during the test, as well as any intermittent or "continuous'' codes set within the previous 20 warm-up cycles. If a code was set before a problem self-corrected (such as a momentarily loose connector), the code will be erased if the problem does not reoccur within 20 subsequent warm-up cycles.

The Quick Test procedure is divided into multiple sections, the most common of which are: Key On Engine Off (KOEO), Key On Engine Running (KOER), and Continuous Testing. Other tests may be performed, including Output State checking and, on SEFI engines, cylinder balance testing. These series of diagnostic procedures must be performed correctly if the system is to run the internal Self-Test checks and provide accurate fault codes.

If the vehicle passes all three sections of the Quick Test, the EEC-IV system is all right and the vehicle's problem exists elsewhere. Once the Quick Test has been performed and all fault codes recorded, refer to the code charts found later in this section.

In all cases, code 11 is used to indicate PASS during testing. Note that the PASS code may appear, followed by other stored codes. These are codes from the Continuous Memory and may indicate intermittent faults, even though the system does not presently contain the fault. The PASS designation only indicates that the system passes all internal tests at the moment.

To prevent injury and/or property damage, always block the drive wheels, firmly apply the parking brake, place the transmission in PARK or NEUTRAL and turn all electrical loads OFF before performing the Quick Test procedures.


See Figure 5

Unless instructed otherwise, do not disconnect any sensor with the key ON or a service code may be stored.

  1. Connect the scan tool or voltmeter to the self-test connectors. When using a STAR tester, make certain the test button is unlatched or up.
  3. Start the engine and run it until normal operating temperature is reached.
  5. Turn the engine OFF for 10 seconds.
  7. Activate the test button on the STAR tester, if applicable. This will ready the Self-Test mode.
  9. Turn the ignition switch ON , but do not start the engine.

Do not depress the throttle on gasoline engines during the test.

  1. The KOEO codes will be transmitted. After the last KOEO code, a single separator pulse will be transmitted. Six to nine seconds after this pulse, the codes from the Continuous Memory will be transmitted.
  3. Record all service codes displayed.

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Fig. Fig. 5: Code transmission during KOEO test. Note that the Continuous Memory codes are transmitted after a pause, a separator code, and another pause.


See Figure 6

Unless instructed otherwise, do not disconnect any sensor with the key ON or a service code may be stored.

  1. Make certain the self-test button is released or de-activated on the STAR tester, if applicable.
  3. Start the engine and run it at 2000 rpm for two minutes. This action warms up the oxygen sensor.
  5. Turn the ignition switch OFF for 10 seconds.
  7. Activate or latch the self-test button on the scan tool, if applicable.
  9. Start the engine. The engine identification code will be transmitted. This is a single digit number representing half the number of cylinders in a gasoline engine. On the STAR tester, this number may appear with a zero (for example, 20 = 2). The code is used to confirm that the correct processor is installed and that the Self-Test has begun.
  11. If the vehicle is equipped with a Brake On/Off (BOO) switch, the brake pedal must be depressed and released after the ID code is transmitted.
  13. If the vehicle is equipped with a Power Steering Pressure Switch (PSPS), the steering wheel must be turned at least 1 / 2 turn and released within 2 seconds after the engine ID code is transmitted.
  15. Certain Ford vehicles will display a dynamic response code 6-20 seconds after the engine ID code. This will appear as one pulse on a voltmeter or as a "10'' on the STAR tester. When this code appears, briefly take the engine to wide open throttle. This allows the system to test the throttle position and vane air flow sensors.
  17. All relevant codes will be displayed and should be recorded. Remember that codes refer only to faults present during this test cycle. Codes stored in Continuous Memory are not displayed in this test mode.
  19. Do not depress the throttle during testing unless a dynamic response code is displayed.

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Fig. Fig. 6: Code transmission during KOER testing begins with the engine identification code, and may include a dynamic response code


Once entered, this mode allows the technician to attempt to recreate intermittent faults by wiggling or tapping components, wiring or connectors. The test may be performed during either KOEO or KOER procedures. The test requires the use of either an analog voltmeter or a hand-held scan tool.

  1. To enter the Continuous Monitor mode during KOEO testing:
    1. Turn the ignition switch ON .
    3. Activate the test, wait 10 seconds, then deactivate and reactivate the test; the system will enter the continuous monitor mode.
    5. Tap, move or wiggle the harness, component or connector suspected of causing the problem; if a fault is detected, the code will store in the memory. When the fault occurs, either the STAR tester will light a red indicator (and possibly beep) or the analog meter needle will sweep once.

  3. To enter this mode in the KOER test:
    1. Start the engine and run it at 2000 rpm for two minutes. This action warms up the oxygen sensor.
    3. Turn the ignition switch OFF for 10 seconds.
    5. Start the engine.
    7. Activate the test, wait 10 seconds, then deactivate and reactivate the test; the system will enter the continuous monitor mode.
    9. Tap, move or wiggle the harness, component or connector suspected of causing the problem; if a fault is detected, the code will store in the memory.
    11. When the fault occurs, either the STAR tester will light a red indicator (and possibly beep) or the analog meter needle will sweep once.



This testing mode allows the operator to energize and de-energize most of the outputs controlled by the EEC-IV system. Many of the outputs may be checked at the component by listening for a click or feeling the item move or engage using a hand placed on the case. To enter this check:

  1. Enter the KOEO test mode.
  3. When all codes have been transmitted, depress the accelerator all the way to the floor and release it.
  5. The output actuators are now all ON. Depressing the throttle pedal to the floor again switches all the actuator outputs OFF.
  7. This test may be performed as often as necessary, switching between ON and OFF by depressing the throttle.
  9. Exit the test by turning the ignition switch OFF , then disconnecting the jumper wire at the diagnostic connector or releasing the test button on the scan tool.


The EEC-IV system allows a cylinder balance test to be performed on engines equipped with the Sequential Electronic Fuel Injection system. Cylinder balance testing identifies a weak or non-contributing cylinder.

Enter the cylinder balance test by depressing and releasing the throttle pedal within 2 minutes of the last code output in the KOER test. The idle speed will become fixed and engine rpm is recorded for later reference. The engine control assembly will shut off the fuel to the highest-numbered cylinder (4 or 8), allow the engine to stabilize and then record the rpm. The injector is turned back on and the next one shut off and the process continues through cylinder No. 1.

The controller selects the highest rpm drop from all the cylinders tested, multiplies it by a percentage and arrives at an rpm drop value for all cylinders. For example, if the greatest drop for any cylinder was 150 rpm, the processor applies a multiple of 65% and arrives at 98 rpm. The processor then checks the recorded rpm drops, checking that each was at least 98 rpm. If all cylinders meet the criteria, the test is complete and the PCM outputs Code 90, indicating PASS.

If one cylinder did not drop at least this amount, then that cylinder number is output instead of the 90 code. The cylinder number will be followed by a zero, so 30 indicates that cylinder No. 3 did not meet the minimum rpm drop.

The test may be repeated a second time by depressing and releasing the throttle pedal within 2 minutes of the last code output. For the second test, the controller uses a lower percentage (and thus a lower rpm) to determine the minimum acceptable rpm drop. Again, either Code 90 or the number of the weak cylinder will be output.

Performing a third test causes the PCM to select an even lower percentage and rpm drop. If a cylinder is shown as weak in the third test, it should be considered non-contributing. The tests may be repeated as often as needed if the throttle is depressed within two minutes of the last code output. Subsequent tests will use the percentage from the third test instead of selecting even lower values.


Continuous Memory Codes

These codes are retained in memory for 20 warm-up cycles. To clear the codes for the purposes of testing or confirming repair, perform the KOEO test. When the fault codes begin to display, de-activate the test by either disconnecting the jumper wire (if using a voltmeter) or releasing the test button on the hand-held scanner. Stopping the test during code transmission will erase the Continuous Memory. Do not disconnect the negative battery cable to clear these codes; the Keep Alive memory will be cleared and a new code (19) will be stored for loss of PCM power.

Keep Alive Memory

The Keep Alive Memory (KAM) contains the adaptive factors used by the processor to compensate for component tolerances and wear. It should not be routinely cleared during diagnosis. If an emissions related part is replaced during repair, the KAM must be cleared. Failure to clear the KAM may cause severe driveability problems since the correction factor for the old component will be applied to the new component.

To clear the Keep Alive Memory, disconnect the negative battery cable for at least 5 minutes. After the memory is cleared and the battery reconnected, the vehicle must be driven at least 10 miles so that the processor may relearn the needed correction factors. The distance to be driven depends on the engine and vehicle, but all drives should include steady-throttle cruising on open roads. Certain driveability problems may be noted during the drive because the adaptive factors are not yet functioning.