Fuel Pump Mercury Topaz I

COMPONENT TESTING

Note. Specific component testing information not available. Refer to any tests performed during REMOVAL & INSTALLATION or OVERHAUL procedures

DESCRIPTION

Two types of fuel pumps are currently used. Most carbureted gasoline vehicles use an engine-mounted mechanical pump. Gasoline vehicles with fuel injection use an electric pump normally located in or near the fuel tank.

Some models use a low pressure electric pump in conjunction with a high pressure electric pump. Usually one pump will be located in the fuel tank, the other externally. This provides adequate fuel delivery during extreme vehicle maneuvers or steep inclines with low fuel tank levels.

Vehicle manufacturers recommend that the pump be replaced as an assembly if found defective. Check pumps for fuel pressure, volume, and vacuum (suction). DO NOT attempt to overhaul or repair pump assembly. Some pumps will have an extra connection for fuel and vapor return to aid in hot starting and prevention of vapor lock.

TESTING

If a complaint is diagnosed as a fuel supply problem, fuel pump, lines, and tank must be tested or inspected before replacing fuel pump. Make the following tests and inspections

FUEL LINES & HOSES

Inspect all metal fuel lines for damage from vibration, impact, or kinking. Inspect rubber hoses for cracks, kinks, or deterioration. If fuel line between engine and fuel tank is suspected of being clogged, disconnect at engine and fuel tank and blow clear with compressed air. NEVER use compressed air on a fuel line which is still connected to a fuel pump.

FILTERS & SCREENS

Inspect and clean (or replace) all filters and screens in both pump inlet and outlet lines and at carburetor/throttle body. In some cases, fuel tank pickup screen can be clogged enough to affect fuel delivery at high speed.

WIRING CONNECTIONS

Inspect all wiring and electrical connections for breaks, loose connections and corrosion. Faulty fuel pump wiring or connections can cause inaccurate testing and diagnosis results.

Mechanical

1. Be sure there is gasoline in the tank. Disconnect ignition wire from distributor.
2. Disconnect fuel line at carburetor inlet fitting. Install length of fuel resistant hose over end of fuel line. Place end of hose into a gasoline container.
3. Crank engine. Compare amount of fuel pumped to specifications for each manufacturer. Pump output should be about 1 pint in 30 seconds.
4. If little or no gasoline flows from hose, check fuel lines or gas tank filter for kinks, restrictions or leaks. If lines and filter are clear, pump is defective and must be replaced.

PRESSURE TEST

Note. The following is only a general procedure. For specific manufacturers electric fuel pump testing procedures, see the appropriate Fuel Injection article in this Section.

Electrical

1. Disconnect fuel line from injector inlet "T". Install a "T" connector with a pressure gauge in the line and reconnect line to injector. Some models are equipped with a fitting which allows pressure test without disconnecting fuel lines.
2. Hold pressure gauge about 16" (406 mm) above fuel pump. Pinch off fuel return line (if equipped). Start engine and observe pressure.
3. After pressure check, reconnect steel line. If pressure is not within specifications or varies greatly, replace fuel pump.

1. Disconnect fuel line from carburetor. Connect line to a pressure gauge. Hold gauge about 16" (406 mm) above pump level. Pinch off fuel return line (if equipped).
2. Start engine and allow to idle (using gas in carburetor bowl). Observe pressure gauge. Pressure should be about 4-7 psi (.28-.49 kg/cm 2 ) for 4 and 6 cylinder engines, and about 6-9 psi (.42-.63 kg/cm 2 ) for V8 engines.
3. Replace pump if pressure is too high or low, or if pressure varies greatly with the engine speed.

1. Reconnect fuel line to carburetor inlet and check for leaks. Disconnect hose at inlet side of fuel pump. Raise end of hose so fuel will not run out. Connect vacuum gauge to pump inlet with short length of hose.
2. Start engine and allow to idle. Check vacuum level. Gauge should read at least 5-7.7 in. Hg. If not, replace pump.

SPECIFICATIONS

FUEL PUMP SPECIFICATIONS (TYPICAL)