Fuel Pressure: Testing and Inspection

OPERATIONAL CHECK (QUICK CHECK):
1. Turn the ignition switch OFF

Fuel Pump Drive Terminal:

2. Apply battery voltage to the fuel pump drive connector to power the fuel pump.
3. Pinch the fuel hose to check that fuel pressure is felt.
NOTE: The fuel pump is mounted in the fuel tank and it operates submerged in fuel, therefore its operating sound is hard to hear without removing the fuel filler cap.


PRESSURE TEST (DIAGNOSTIC CHECK):
1. Reduce the internal pressure of the pipes and hoses by the following procedures.
a. Disconnect the fuel pump harness at the rear of the fuel tank.
b. Start and run the engine until it stalls. Turn OFF the ignition key.
c. Disconnect the battery negative terminal.
d. Connect the fuel pump harness connector.

Fuel High Pressure Hose Connection:

2. Disconnect the high pressure fuel hose at the delivery end.
CAUTION: Cover the hose connector with a shop towel to prevent splashing of fuel caused by residual pressure in the fuel line.

Fuel Pressure Test Equipment:

Fuel Pressure Test Connection:

3. Using the fuel pressure gauge adapter (MD998742-01) or equivalent, install the fuel-pressure gauge at the delivery pipe (fuel rail).
4. Connect the battery negative terminal.
5. Apply battery power to the fuel pump drive terminal to activate the fuel pump. With fuel pressure applied check that no fuel is leaking at any of the connections.

Fuel Pressure Regulator, Vacuum Hose Removed:

6. Disconnect the vacuum hose from the pressure regulator, and plug the hose end. Measure the fuel pressure at idle.

Standard Value: 35.6-38.4 psi (245-264 kPa)

7. Measure the fuel pressure when the vacuum hose is connected to the pressure regulator.

Standard Value: 28.4 psi (196 kPa).

8. If the results of the measurements made in steps 6 and 7 are not within the standard values, refer to the symptoms listed below to determine the probable cause and make the necessary repairs before re-testing.
a. Fuel pressure too low:
1. Clogged fuel filter---Replace
2. Fuel bleeds down to return hose---Replace the fuel pressure regulator
3. Low pump output pressure---Check for leak in-line (could be leaking inside the fuel tank) or bad fuel pump.
b. Fuel pressure too high:
1. Regulator stuck closed---Replace the fuel pressure regulator
2. Clogged or bent fuel return hose---repair hose
c. No difference with or without vacuum connected:
1. Non-responsive regulator---Replace the fuel pressure regulator
2. Plugged vacuum line or no source vacuum---replace line or repair vacuum source
9. Stop the engine and check for a change in fuel pressure readings. Pressure should hold for 5 minutes. If the gauge reading drops, observe the rate of drop. Determine the cause according to the following symptoms.
a. Fuel pressure drops slowly:
1. Injector leakage---Identify leaking injector and replace.
2. Regulator is leaking to return line---Confirm and replace regulator.
3. Check valve in the fuel pump is leaking---Replace the pump.
b. Fuel pressure drops immediately:
1. Regulator is leaking to return line---Confirm and replace regulator.
2. Check valve in the fuel pump is open---Replace the pump.