About 1 1/2 years ago I replaced the fuel pump on my '95 Explorer. That didn't fix it right away. However, over the last six months my car's been starting like a champ. But lately (3 weeks) it will crank all day but it won't start unless I hear a short hum sound. I've been doing a little research about testing the fuel system pressure. I would try that but I don't have a pressure gauge. Also, before I forget, if I'm sitting at a red light idling and I turn on the defrost or the a/c, the car will die right then and there. I'm hoping it's something that I can do myself. I'll invest in a pressure gauge. Also can you tell me what my fuel system's pressure should be?
Thanks for any advice you can give me.
Fuel is supplied by an in-tank electric fuel pump. See Fig. 1 . Pump has a discharge check valve to maintain system pressure during shutdown and minimize starting problems.
Pump delivers fuel from fuel tank through fuel filter to fuel charging manifold assembly (fuel rail). Fuel charging manifold assembly incorporates electrically actuated fuel injectors directly above each intake port. Injectors spray metered quantity of fuel into intake air stream. Constant fuel pressure to injector nozzles is maintained by fuel pressure regulator.
Fuel Delivery Assembly (FDA)
The FDA consists of a fuel pump inside a reservoir that is attached to the pump and sender assembly. See Fig. 2 . In a 2-tank system there is one FDA per tank. Fuel sender assembly handles the fuel switching through internal valves.
Fuel reservoir is used to prevent fuel flow interruptions during extreme vehicle maneuvers when fuel tank level is low. Reservoir is located in-tank and is either molded or welded into fuel tank or is part of FDA.
Shuttle valve opens fuel return line to fuel tank when fuel pressure on shuttle diaphragm exceeds opposing check valve spring force. When pump is de-energized, supply check valve closes to maintain pump prime and fuel supply line pressure.
A portion of high pressure flow from the pump is diverted to operate the venturi jet pump. The jet pump draws fuel from the tank into the FDA. This ensures adequate fuel supply during extreme vehicle maneuvers and steep vehicle attitudes when fuel level is low. If FDA is defective, it must be replaced as an assembly.
Fuel Supply Manifold Assembly
Fuel supply manifold assembly (fuel rail) delivers high pressure fuel from fuel pump supply line to fuel injectors. Fuel pressure regulator is mounted on flange attached to rail.
Fuel Pressure Regulator
The fuel pressure regulator is attached to fuel supply manifold assembly, downstream of fuel injectors. It regulates fuel pressure supplied to injectors. Regulator is a diaphragm-operated valve with one side responding to fuel pressure and the other side to intake manifold vacuum.
When intake manifold vacuum is low, an internal spring increases pressure on diaphragm, blocking off fuel return passage and increasing fuel pressure. When manifold pressure is high, spring pressure is overcome by vacuum, opening fuel return passage and lowering fuel pressure. Excess fuel is by-passed through regulator and returned to fuel tank.
Fuel Pump Activation
When ignition switch is turned to START position, PCM operates fuel pump relay to provide fuel for starting engine. PCM senses engine speed and shuts off fuel pump by opening ground circuit to fuel pump relay when engine stops or engine speed drops to less than 120 RPM. When ignition switch is in ON position, EEC power relay is energized (contacts closed). Power is provided to fuel pump relay and timer in PCM. Fuel pump receives power through fuel pump relay contacts.
Inertia Fuel Shutoff (IFS) Switch
All models use an electrical interrupt switch in fuel system. During a collision or vehicle rollover, electrical contacts within inertia switch open, shutting off fuel supply to electric fuel pump. Fuel supply is interrupted even when engine is running.
A reset button is located on switch assembly. If electrical circuit trips, vehicle will not restart until switch is reset. Fuel system should be inspected before resetting switch.
IFS switch is located under instrument panel, near right side of transmission hump.
NOTE:After an accident, DO NOT reset IFS switch until entire fuel system has been inspected for leaks.
Precise fuel metering is accomplished with EEC-IV system. The PCM continually monitors engine operating conditions based on information received from various sensors and switches. In response to information received, PCM calculates optimum air/fuel mixture in relation to present engine operating conditions and affects required metering adjustments through output actuators control.
The PCM controls fuel injectors to meter pulse width or time each injector is energized. Each injector receives battery voltage through ignition switch circuit. The PCM-controlled ground circuit completes circuit to energize injector. The PCM receives inputs from engine sensors to compute fuel flow necessary to maintain air/fuel mixture ratio throughout entire engine operational range.
Each cylinder has a solenoid-operated injector which sprays fuel toward back of each intake valve. Injector bodies consist of solenoid-actuated pintle and needle valve assembly.