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Diagnostic Aids

WARNING: This page is about a different car, the 1995 Ford Explorer and 1995 Ford Aerostar. However, it is still accessible from the selected car via links, so may be relevant.

Enter this test when directed by QUICK TEST. This test is only intended to diagnose:

Purpose of octane adjust shorting bar is to provide optimum spark advance for fuel used. If engine detonates (spark knock), remove octane shorting bar. This retards spark advance about 3-4 degrees. If engine continues to detonate, use fuel with a higher octane rating.

Fig 1: Octane Adjust Circuit (4.0L)
G93J40757
OCT ADJ WIRE COLOR & TEST PIN IDENTIFICATION

Application Test Pin No. Wire Color
Aerostar 44 Dark Green
Explorer 29 Dark Green
TEST PIN NO. 46 (SIG RTN) WIRE COLOR IDENTIFICATION

Application Wire Color
All Models Gray/Red

1) Code 341  Code 341 indicates octane adjust shorting bar is not in place or OCT ADJ circuit is open. Turn ignition off. Inspect octane adjust in-line connector. If shorting bar has been removed, go to next step. If shorting bar is in place, go to step 4).

2) Check For Modification Decal  If vehicle has modification decal indicating octane adjust shorting bar was removed as a factory authorized procedure, testing is complete. If engine is detonating, go to appropriate TESTS W/O CODES (EEC-IV) article in the ENGINE PERFORMANCE section below. If vehicle does not have modification decal, go to next step.

3) Check For Code 341  Replace octane adjust shorting bar. Perform KOEO SELF-TEST. If Code 341 is present, go to next step. If code is not present, testing is complete. If driveability faults are present, go to appropriate TESTS W/O CODES (EEC-IV) article in the ENGINE PERFORMANCE section below.

4) Check Octane Adjust Circuit Continuity  Continuity should exist from OCT ADJ circuit, through in-line connector and shorting bar, to SIG RTN circuit. Turn ignition off. Disconnect 60-pin PCM connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between test pin No. 46 and OCT ADJ test pin at breakout box. If resistance is more than 5 ohms, repair open OCT ADJ circuit, shorting bar or SIG RTN circuit. Repeat QUICK TEST. If resistance is 5 ohms or less, replace PCM and repeat QUICK TEST.

5) Check For Code 111  Start engine. Warm to normal operating temperature. Turn ignition off. Perform KOEO SELF-TEST. If Code 111 is present, go to next step. If Code 341 is present, return to step 1). For all other codes, return to QUICK TEST.

6) Verify In-Line Shorting Bar Is Installed  Turn ignition off. Inspect octane adjust in-line connector. If shorting bar is installed, go to step 8). If shorting bar is not installed, go to next step.

7) Check For Modification Decal  If vehicle has modification decal indicating octane adjust shorting bar was removed as a factory authorized procedure, testing is complete. If engine is detonating, go to appropriate TESTS W/O CODES (EEC-IV) article in the ENGINE PERFORMANCE section. If vehicle does not have modification decal, go to step 10).

8) Check For Technical Service Bulletin (TSB)  If a TSB authorizing removal of octane adjust shorting bar exists, go to next step. If a TSB authorizing removal of octane adjust shorting bar does not exist, testing is complete. If driveability faults are present, go to appropriate TESTS W/O CODES (EEC-IV) article in the ENGINE PERFORMANCE section.

9) Remove Octane Adjust Shorting Bar  Turn ignition off. Remove octane adjust shorting bar. Test drive vehicle to verify complaint. If detonation is present, go to next step. If detonation is not present, system is okay. Testing is complete.

10) Check Octane Adjust Circuit For Short To Ground  Turn ignition off. Disconnect 60-pin PCM connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between OCT ADJ terminal at in-line connector and test pins No. 40, 46 and 60 at breakout box. If resistance is 10,000 ohms or less, repair short circuit and repeat QUICK TEST. If each resistance is more than 10,000 ohms, go to next step.

11) Check PCM  Turn ignition off. Disconnect octane adjust shorting bar. Turn ignition on. Measure voltage between OCT ADJ test pin terminal and test pins No. 40 and 60 at breakout box. If voltage is 4 volts or less, replace PCM. Repeat QUICK TEST. If engine still detonates, go to appropriate TESTS W/O CODES (EEC-IV) article in the ENGINE PERFORMANCE section. If voltage is more than 4 volts, remove breakout box and go to appropriate TESTS W/O CODES (EEC-IV) article in the ENGINE PERFORMANCE section.

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