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.
1990 Ford Bronco II RWD, Standard, M5OD-R1FACTORY OEM SERVICE PROCEDURE
Fuel Pump Relay Power Check
- Turn ignition on. Use voltmeter to measure voltage between ground and terminals "B" (Red) and "C" (Black/Yellow) or "A" (Yellow). See Figure . If voltage at each terminal is more than 10.5 volts, voltage supply is okay. Proceed to FUEL PUMP RELAY RESISTANCE CHECK . If voltage reading is 10.5 volts or less, proceed to steps 2 and 3.
- If voltage at terminal "B" (Red) is less than 10.5 volts, repair fuel pump relay-to-EEC power relay circuit. If the voltage at terminal "C" (Black/Yellow) is less than 10.5 volts, check 30-amp fuse in power distribution box. If fuse is okay, repair Black/Yellow wire between power distribution box and fuel pump relay.
- If the voltage at terminal "A" (Yellow) is less than 10.5 volts, check circuit between fuel pump relay and Batt (+). Repair as necessary. If circuit is okay, perform QUICK TEST in TESTS W/CODES article.
Factory Service Tools
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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