The Ford fuel system resembles the design and type on most vehicles used today. On the more modern cars and trucks, the gas tank contains a pump that sends fuel through the lines, which contain filters, and then onto the throttle body or fuel rail. A fuel pressure regulator controls the amount of fuel sent back into the system. Any one of the components can contribute to a problem. Diagnosing a fuel flow problem requires a process of elimination, which means ruling out a good working part and finding the defective component.
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Things you need
- Owner's repair manual
- Floor jack
- Jack stands
- Flexible hose
- Fuel pressure gauge
- Fuel line wrenches
- Drain pan
Set the vehicle shifter in park or neutral, according to your transmission type. Apply the emergency brake. Raise the bonnet. Use a floor jack to raise the vehicle rear end and place two jack stands under the chassis frame. Raise the front end of the vehicle and set two jack stands under the chassis frame.
Remove the gas tank cap and insert a flexible hose down the inlet neck as far as it will go, but do it gently. Pull the hose out and visually check for wetness on the hose, which will rule out a defective gas gauge on the dashboard. Be certain to tighten the gas cap properly -- a loose gas cap that works under pressure will affect the fuel flow delivery. Start the engine and slide under the gas tank.
Hold a stethoscope to the uppermost part of the tank and listen for a humming sound, which will be the electric fuel pump. No sound will usually indicate a defective circuit wire to the pump or a bad fuel pump motor. Go to your main fuse box panel; refer to your owner's manual for its location. Pull the fuse box lid and look at the schematic for the fuel pump relay and/or fuse.
Check the fuse for a blown filament. Replace any blown fuse. Exchange the fuel pump relay with another one of identical design that currently runs another component. With the engine running, listen with the stethoscope again. If you can hear a humming sound, the fuse or relay was defective. Shut off the engine.
Move to the engine compartment and locate the test port Schrader valve on the fuel rail. Check your owner's manual for its location. Place a rag over the Schrader valve. Unscrew the Schrader valve cap and use a screwdriver tip to release the fuel pump pressure. Replace the cap. Loosen the fuel intake line with a fuel wrench. Hook up a fuel pressure gauge to a T-fitting, connecting the top of the T-fitting lines to the tank side line and the injector side line.
Turn the ignition key to the "On" position. Read the gauge. For a fuel port injection system, the psi (pounds per square inch) should read 45 to 55 psi. For a throttle body fuel system, it should read 14 to 18 psi. Anything reading less will indicate a problem with the fuel pump, intake line or in-line fuel filter underneath the chassis. Turn off the ignition key.
Start the engine, with the fuel pressure gauge still attached. The psi readings should not change from your specifications. Work the throttle lever or pull the throttle cable to rev the engine once. Look at the gauge. The psi should jump up about 2.27kg. above your normal fuel specification pressure. If the pressure did not jump up when you revved the engine, the fuel pressure regulator has failed and needs replacement.
Slide under the vehicle and check the fuel line running from the front of the engine to the gas tank. Look for kinks, cuts or damage in the flexible hose or solid line. Locate the in-line fuel filter under the chassis by referring to your owner's manual. Place a drain pan under the filter. Use a screwdriver to loosen the hose clamps on the filter.
Pull out the filter and blow through both nozzle ends. A clogged filter will not allow air to pass from one or both sides. Replace the filter with a new one, if clogged. Use a screwdriver to reattach the old filter to the fuel hoses if it checks out.
Tips and warnings
- If you have eliminated the gas tank level, the fuel pump, fuel filter and fuel pressure regulator as the problem components, you will have to pull the fuel rail and check each individual fuel injector head. This procedure should be done at a shop, where nozzle pressures and spray patterns can be evaluated by a technician, under a Plexiglas canopy.
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