Symptoms Suggesting a Bad Fuel Pump:
* No Start: This is the most obvious sign. The engine cranks but won't fire because it's not getting fuel.
* Hard Starting (especially when hot): The pump might be weakening and struggling to deliver enough fuel under pressure.
* Engine Stalling/Hesitation: Intermittent stalling, especially under acceleration, suggests the pump isn't supplying fuel consistently.
* Reduced Power/Performance: A weak pump may not be able to keep up with fuel demand under load.
* Whining Noise from the Tank: You might hear a whining or buzzing sound coming from the fuel tank when the ignition is turned on. This is the pump's motor working. A loud, abnormal noise could indicate problems. (This is less reliable as pumps can fail silently).
* Fuel Pressure Issues (requires gauge): This is the most definitive test. You'll need a fuel pressure gauge to measure the pressure at the fuel rail. The specifications for your 1990 F-150's fuel pressure are in your owner's manual or a repair manual. Low or fluctuating pressure points directly to the pump.
Testing Procedures (in order of least to most invasive):
1. Check the Fuel: The simplest thing first – is the fuel tank actually low on gas? An empty tank will obviously prevent starting.
2. Listen for the Fuel Pump: Turn the ignition key to the "ON" position (don't start the engine). You should hear a brief humming sound from the fuel tank area. If you don't hear anything, the pump might be dead or the inertia switch is tripped.
3. Check the Inertia Switch: This is a safety device that cuts the fuel supply in a collision. Locate the inertia switch (usually under the dash or in the engine bay – consult your owner's manual) and reset it if it's tripped (usually a small button to push).
4. Inspect the Fuel Filter: A clogged fuel filter can restrict fuel flow and mimic symptoms of a bad pump. Replace the filter if it's dirty. This is a relatively cheap and easy fix.
5. Check Fuel Pressure (Requires Gauge): This is the most definitive test. You'll need a fuel pressure gauge and the correct adapter to connect it to the fuel rail. Compare your reading to the specifications in a repair manual. Low or inconsistent pressure strongly suggests a bad fuel pump.
6. Visual Inspection (Advanced): If the above steps don't reveal the problem, you might need to remove the fuel tank to inspect the pump itself for damage or corrosion. This is a more involved process and should only be attempted if you have experience with automotive repair.
Important Note: Gasoline is highly flammable. Always work in a well-ventilated area and take proper precautions to prevent fires. If you're not comfortable performing these checks yourself, take your truck to a qualified mechanic. They have the tools and expertise to diagnose the problem accurately and safely.
