Inspect and replace, if necessary, all underhood hoses Ford F150

Warning: Replacement of air conditioning hoses must be left to a dealer service department or air conditioning shop that has the equipment to depressurize the system safely and recover/recycle the refrigerant. Never remove air conditioning components or hoses until the system has been depressurized and the refrigerant recovered.


1. High temperatures under the hood can cause deterioration of the rubber and plastic hoses used for engine, accessory and emission systems operation. Periodic inspection should be made for cracks, loose clamps, material hardening and leaks.

2. Information specific to the cooling system hoses can be found in Inspect the cooling system.

3. Most (but not all) hoses are secured to the fittings with clamps. Where clamps are used, check to be sure they haven’t lost their tension, allowing the hose to leak. If clamps aren’t used, make sure the hose has not expanded and/or hardened where it slips over the fitting, allowing it to leak.

PCV system hose

4. To reduce hydrocarbon emissions, crankcase blow-by gas is vented through the PCV valve in the valve cover to the intake manifold via a rubber hose (or plastic quick-connect tube) on most models. The blow-by gases mix with incoming air in the intake manifold before being burned in the combustion chambers.

5. Check the PCV hose for cracks, leaks and other damage. Disconnect it from the valve cover and the intake manifold and check the inside for obstructions. If it’s clogged, clean it out with solvent.

6. For information specific to the PCV valve, see Check the PCV valve.

Vacuum hoses

7. It’s quite common for vacuum hoses, especially those in the emissions system, to be color coded or identified by colored stripes molded into them. Various systems require hoses with different wall thickness, collapse resistance and temperature resistance. When replacing hoses, be sure the new ones are made of the same material.

8. Often the only effective way to check a hose is to remove it completely from the vehicle. If more than one hose is removed, be sure to label the hoses and fittings to ensure correct installation.

9. When checking vacuum hoses, be sure to include any plastic T-fittings in the check. Inspect the fittings for cracks and the hose where it fits over each fitting for distortion, which could cause leakage.

10. A small piece of vacuum hose (1/4-inch inside diameter) can be used as a stethoscope to detect vacuum leaks. Hold one end of the hose to your ear and probe around vacuum hoses and fittings, listening for the «hissing» sound characteristic of a vacuum leak. Warning: When probing with the vacuum hose stethoscope, be careful not to come into contact with moving engine components such as drivebelts, the cooling fan, etc.

Fuel hose

Warning: Gasoline is flammable, so take extra precautions when you work on any part of the fuel system. Don’t smoke or allow open flames or bare light bulbs near the work area, and don’t work in a garage where a gas-type appliance (such as a water heater or clothes dryer) is present. Since fuel is carcinogenic, wear fuel-resistant gloves when there’s a possibility of being exposed to fuel, and, if you spill any fuel on your skin, rinse it off immediately with soap and water. Mop up any spills immediately and do not store fuel-soaked rags where they could ignite. The fuel system is under constant pressure, so, if any fuel lines are to be disconnected, the fuel pressure in the system must be relieved first (see Chapter 4 for more information). When you perform any kind of work on the fuel system, wear safety glasses and have a Class B type fire extinguisher on hand.

11. The fuel lines are usually under pressure, so if any fuel lines are to be disconnected be prepared to catch spilled fuel. Refer to Chapter 4 for the fuel system pressure relief procedure.

Warning: Your vehicle is equipped with fuel injection and you must relieve the fuel system pressure before servicing the fuel lines.

12. Check all flexible fuel lines for deterioration and chafing. Check especially for cracks in areas where the hose bends and just before fittings, such as where a hose attaches to the fuel pump, fuel filter and fuel injection unit.

13. When replacing a hose, use only hose that is specifically designed for your fuel injection system.

14. Spring-type clamps are sometimes used on fuel return or vapor lines. These clamps often lose their tension over a period of time, and can be «sprung» during removal. Replace all spring-type clamps with screw clamps whenever a hose is replaced. Some fuel lines use spring-lock type couplings, which require a special tool to disconnect. See Fuel and exhaust systems for more information on this type of couplings.

Metal lines

15. Sections of metal line are often used for fuel line between the fuel pump and the fuel injection unit. Check carefully to make sure the line isn’t bent, crimped or cracked.

16. If a section of metal fuel line must be replaced, use seamless steel tubing only, since copper and aluminum tubing do not have the strength necessary to withstand vibration caused by the engine.

17. Check the metal brake lines where they enter the master cylinder and brake proportioning unit (if used) for cracks in the lines and loose fittings. Any sign of brake fluid leakage calls for an immediate thorough inspection of the brake system.

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