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
High Pressure Fuel Pump Testing
CAUTION:
Fuel system is under pressure. Before removing any 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. Install fuel pressure gauge. Turn ignition switch to the "RUN" position. Ground jumper lead and check fuel pressure. See FUEL PRESSURE SPECIFICATIONS . If fuel pressure is within specification, go to step 5). If fuel pressure is not within specification, go to step 2).
- If fuel pressure is low but greater than 3 psi (indicates pump is working), go to step 3). If not, go to step 4).
- Check fuel system for plugged fuel filter or restricted fuel lines. Check for low voltage at the fuel pump (voltage should be with .5 volt of battery voltage). Disconnect fuel return line. If fuel is returning , replace pressure regulator. If filters are clear, voltage correct and no fuel return, replace fuel pump.
- Ensure that battery voltage and ground are present at fuel pump connector. If circuits and voltages are correct, replace fuel pump.
- Disconnect grounded test lead and note fuel pressure. Fuel pressure should remain within 3 psi for 3 minutes after disconnecting test lead. If fuel pressure holds, go to step 7). If not, go to step 6).
- Inspect for fuel leaks. If no leaks are found, disconnect and plug fuel return line. Ground test lead and raise pressure to normal level. If fuel pressure now holds, replace pressure regulator. If not, replace fuel pump.
- Disconnect vacuum to fuel pressure regulator and start engine. Fuel pressure should be within specification. See FUEL PRESSURE SPECIFICATIONS . If fuel pressure is correct, go to step 9). If fuel pressure is not, go to step 8).
- If fuel pressure is low, check fuel filter, fuel pressure regulator adjustment, fuel line restrictions or voltage to fuel pump. If all systems are normal, replace fuel pump.
- With engine idling and fuel pressure regulator vacuum hose disconnected, measure fuel pressure. Accelerate rapidly and note fuel pressure. If fuel pressure drops more than 5 psi, repeat step 8). If fuel pressure does not drop, fuel system is operating correctly.
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.