Questionwhere is the fuel pressure regulator on a 1995 nissan pathfinder and how do you test it to see if it is the regulator or the fuel pump.
AnswerHi Mike -
Here is a detailed test for your fuel system -
Hope this helps -
aloha
calvin
If the pressure is not too far off, the computer will adjust the air/fuel mixture after the system begins closed loop operation. The vehicle will have a cold driveability problem that will disappear when it is warm.
To test fuel pressure, the pump must be operating. If it is not, check the fuel pump fuse.
On Fords there is an inertia switch in the circuit that powers the fuel pump.
Push the reset button on it first to see if the problem goes away.
It is possible that a fuel pump produces the specified pressure when the key is turned on or at engine idle, but does not produce enough pressure under load.
If the engine cuts out at higher speeds, the car should be road tested with a pressure gauge installed.
A pressure gauge with a long hose can be taped to the windshield so it can be viewed from the passenger compartment.
NOTE
Before a pressure gauge is installed, relieve the pressure in the fuel system.
Installing Pressure Gauge on TBI (Throttle Body Injection) Systems
Testing pressure in one type of throttle body fuel injection requires that the line entering the throttle body be disconnected.
A pressure gauge is installed in series with the line.
A pressure gauge is installed in the fuel line.
Another testing method recommended by some manufacturers is to install a gauge in series with the fuel filter inlet.
A fuel pressure gauge in series with the fuel filter inlet.
After the gauge is disconnected, install new gaskets on the banjo fitting.
Copper gaskets are reusable if not damaged or imprinted.
Installing Pressure Gauge on PFI (Port Fuel Injection) Systems
In port fuel injection systems, the gauge is installed at the Schrader valve on the fuel rail or on the fuel line to the cold start injector.
A gauge is installed in the fuel pressure test port on the fuel rail. Courtesy of Chrysler Corporation.
A gauge is installed into the hose connection for the cold start injector.
To perform the pressure test, the fuel pump is energized.
One method is to run the engine at idle speed. Another way is to cycle (turn on and off) the ignition key several times.
Sometimes the engine will not run and it may be necessary to energize the pump electrically. Procedures vary between manufacturers.
Fuel pressure must be at least equal to manufacturer's specifications.
Low Pressure Readings
Causes of low pressure could be a plugged fuel tank inlet sock, a kinked inlet line, or a bad auxiliary pump (some mechanical systems use an auxiliary pump in the fuel tank to push fuel to a higher pressure pump outside of the tank).
When pressure is too low, a fuel pressure regulator could also be the cause. Fuel pressure regulators usually fail by causing pressure that is too low, rather than too high.
High Pressure Readings
High fuel pressure readings will result in a rich-running engine. A restricted fuel return line to the tank or a bad duel regulator may be the problem.
There are two tests for determining the cause of high pressure:
Test 1
To isolate the cause of high pressure, relieve system pressure and connect a tap hose to the fuel return line.
Direct the hose into a container and energize the fuel pump.
If fuel pressure is now within specifications, the fuel return line is blocked.
If pressure is still high, the pressure regulator is faulty.
If the first fuel pressure reading is within specs, but the pressure slowly bleeds down, there may be a leak in the fuel pressure regulator, fuel pump check valve, or the injectors themselves.
Test 2
High pressure is usually caused by a bad pressure regulator or when a pressure return line to the fuel tank is kinked.
When there is a vacuum line to the pressure regulator, part of the procedure is to pull the vacuum hose off while the engine idles.
The pressure should rise about 10 psi in most systems when the hose is pulled.
If a pressure regulator requires adjustment, something else might be wrong with the system. On non-adjustable systems, the regulator must be replaced if the pressure is not correct.
Repeat the test by pressurizing the system and then pinching off the fuel line from the pump. If the pressure remains steady, the check valve is leaking.
To test to see if pressure is leaking through the pressure regulator, plug the fuel return line and repeat the test. If the pressure remains constant, the pressure regulator is leaking.
Leakage Test
During a system pressure test when the fuel pump is turned off, pressure in the system should remain constant for the next startup. If pressure drops while the engine is off, remove the fuel rail and repressurize it. The injectors should not leak.
If the injectors do not leak but pressure on the fuel gauge drops, the check valve in the fuel pump could be leaking.
Repeat the test by pressurizing the system and then pinching off the fuel line from the pump.
If the pressure remains steady, the check valve is leaking.
To test to see if pressure is leaking through the pressure regulator, plug the fuel return line and repeat the test.
If the pressure remains constant, the pressure regulator is leaking.
If pressure leaks from the system, cycling of the ignition switch more than once is often required before starting the engine. This is because more than two seconds of pump operation might be required to fill the fuel rail.
Other Tests
A cause of a rich mixture is a leaking fuel pressure regulator. If the diaphragm of the regulator is ruptured, fuel will move into the intake manifold through the diaphragm, causing a rich mixture. The regulator can be checked by using two simple tests.
After the engine has been run, disconnect the vacuum line to the fuel pressure regulator.
Location of a fuel pressure regulator on an in-line EFI engine.
If there are signs of fuel inside the hose or if fuel comes out of the hose, the regulator's diaphragm is leaking.
The regulator can also be tested with a hand-operated pump. Apply 5 in. Hg (127 mm Hg) to the regulator. A good regulator diaphragm will hold that vacuum.
