Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1987 Ford Mustang L4-140 2.3L SOHCFACTORY OEM SERVICE PROCEDURE
Engine Running Test
1. Start and operate engine at approximately 1500 RPM for 2 minutes to allow EGO sensor to reach normal operating temperature.
2. Turn ignition switch to OFF position and depress self-test button on STAR tester. The colon should appear in the tester display window.
3. Wait approximately 10 seconds, then start engine.
4. The first code to appear in the display window should be an engine identification code (20, 30 or 40).
5. After the engine identification code has appeared, the next code (dynamic response code 10) will appear. Within 15 seconds of receiving a code 10, momentarily place throttle in wide open position, then quickly allow throttle to return to idle position.
6. After the code 10 appears, the fast codes will follow. The fast codes will be viewed only as a slight flicker of the LED on the STAR tester. If the throttle is not momentarily placed in the wide open position with 15 seconds from the time the dynamic response code appears and quickly returned to idle, a code 77 will be displayed. Refer to Self-Test Service Codes.
7. If the system checks out satisfactorily for hard faults, a code 11 (system pass) will appear in the display window. This code indicates that there are no hard faults in any of the system outputs. This part of the self-test does not check for intermittent faults.
8. Any other codes displayed should be noted. These codes indicate that a hard fault in one or more of the system outputs exists. Repeat this test to verify that these codes exist.
9. Compare service codes obtained during this part of the self-test to the instructions described in the appropriate Quick Test procedure charts. Repair all hard faults as required.
10. Repeat Key-ON/Engine-OFF test part if intermittent faults were detected. Repair intermittent faults at this time.
Factory Service Tools
Use the Manual With the Right Hardware
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- β’ You smell fuel, burning insulation, or see smoke.
- β’ Brakes feel soft, pull hard to one side, or make grinding noises.
- β’ The engine overheats, stalls repeatedly, or misfires under load.
- β’ You are missing required tools, torque specs, or safe lifting equipment.
- β’ You are not confident in the next step or safety outcome.
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