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 4WD, Standard, M5OD-R1FACTORY OEM SERVICE PROCEDURE
Low Pressure Fuel Pump Testing
CAUTION:
Fuel system is under pressure. Before removing and fuel lines, depressurize fuel system. Disconnect inertia switch and crank engine for a minimum of 15 seconds to depressurize system.
- Check fuel tank(s) for adequate fuel supply. Check for fuel leaks at fittings and lines. Install jumper lead to fuel pump test terminal of VIP test connector. See Figure . Use a test lead long enough to reach under vehicle. Raise vehicle and ground test lead. Use a stethoscope and listen for pump operation. If low pressure pump is running, go to step 2). If not, go to step 3).
- Disconnect test lead from ground. Remove reservoir inlet hose at reservoir. Place fuel hose in one quart calibrated container and ground test lead for 5 seconds. Fuel level should be at least 6 ounces. If fuel pump volume is correct, fuel pump is okay. If not, restrict fuel line momentarily to prime pump. If no flow develops, check for blocked fuel lines. If no blockage is found, replace pump.
- If pump does not run, inspect all electrical connections. Check inertia switch and fuel pump relay for operation. If high pressure pump runs, but low pressure pump does not and voltage is present, replace low pressure fuel pump.
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.
