Refer to
Fuel Tank Module
Circuit Description
When the ignition switch is turned on, the Powertrain Control Module (PCM) will turn on the in-tank fuel pump. The in-tank fuel pump will remain on as long as the engine is cranking or running and the PCM is receiving reference pulses. If there are no reference pulses, the PCM will turn off the in-tank fuel pump after 2 seconds, or 2 seconds after the engine stops running. The in-tank fuel pump is an electric pump within an integral reservoir. The in-tank fuel pump supplies fuel through an in-line fuel filter to the fuel rail assembly. The fuel pump is designed to provide fuel at a pressure above the pressure that is needed by the fuel injectors. A fuel pressure regulator, attached to the fuel rail assembly, keeps the fuel available to the fuel injectors at a regulated pressure. The unused fuel is returned to the fuel tank by a separate fuel return pipe.
Test Description
The numbers below refer to step numbers on the diagnostic table.
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In order to relieve the fuel pressure, go to Fuel Pressure Relief . When the ignition switch is on and the fuel pump is running, the fuel pressure indicated by the fuel pressure gauge should be 358-405 kPa (52-58 psi).
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A fuel system that drops more than 5 psi in 10 minutes has a leak in one or more of the following areas:
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Fuel pressure that drops-off during acceleration, cruise, or hard cornering may cause a lean condition. A lean condition can cause a loss of power, surging, or a misfire. You can use a scan tool in order to diagnose a lean condition. If an extremely lean condition occurs, the oxygen sensors will stop toggling. The oxygen sensor output voltages will drop to less than 500 mV. Also, the fuel injector pulse width will increase.
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When the engine is idling, the manifold pressure is low (high vacuum). This low pressure (high vacuum) is applied to the fuel pressure regulator diaphragm. The low pressure (high vacuum) will offset the pressure being applied to the fuel pressure regulator diaphragm by the spring inside of the fuel pressure regulator. This will cause lower fuel pressure. The fuel pressure at idle will vary slightly as the barometric pressure changes, but the fuel pressure at idle should always be less than the fuel pressure noted in Step 2 with the engine turned off
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A rich condition may result from the fuel pressure being above 405 kPa (58 psi). A rich condition can cause a DTC P0132 or a DTC P0172 to set. Driveability conditions associated with rich conditions can include hard starting followed by black smoke, and a strong sulfur smell in the exhaust.
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This test determines if the high fuel pressure is due to a restricted fuel return pipe or if the high fuel pressure is due to a malfunctioning fuel pressure regulator.
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A fuel pressure of less than 358 kPa (52 psi) can cause a lean condition. A lean condition may cause a DTC P0131 or a DTC P0171 to set. Driveability conditions associated with lean conditions can include hard starting when the engine is cold, a hesitation, reduced driveability, a lack of power, surging, and misfiring.
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Restricting the fuel flow causes the fuel pressure to rise above the regulated fuel pressure. Using a scan tool in order to pressurize the system, the fuel pressure should rise to more than 405 kPa (58 psi) as the gauge outlet hose is pinched.
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Inspect the spark plug that is associated with a particular fuel injector for fouling or saturation in order to determine if that fuel injector is leaking.
| • | The fuel pump check valve |
| • | The fuel pump flex pipe |
| • | The fuel injectors |
Step | Action | Values | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | |||||||||||
Important: To avoid false fuel pressure readings, thoroughly bleed all air out of the fuel pressure gauge. Important: The fuel pump will run for approximately 2 seconds. Cycle the ignition switch as necessary in order to achieve the highest possible fuel pressure. Is the fuel pressure within the specified range? | 358-405 kPa (52-58 psi) | Go to Step 3 | Go to Step 12 | |||||||||||
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Important: The fuel pressure may vary slightly when the fuel pump stops running. The fuel pressure should stabilize and remain constant. Observe the fuel pressure after the fuel pump stops running. Does the fuel pressure drop more than the specified value within 10 minutes? | 34 kPa (5 psi) | Go to Step 10 | Go to Step 4 | |||||||||||
4 |
Does the fuel pressure drop more than the second specified value within 10 minutes? | 69 kPa (10 psi) 14 kPa (2 psi) | Go to Step 21 | Go to Step 5 | ||||||||||
Is the fuel pressure suspected of dropping-off during any of the following conditions?
| -- | Go to Step 6 | Go to Step 8 | |||||||||||
6 | Visually and physically inspect the following items for a restriction:
Did you find a restriction? | -- | Go to Step 24 | Go to Step 7 | ||||||||||
7 |
Did you find a problem in any of these areas? | -- | Go to Step 24 | Go to Step 21 | ||||||||||
Is the fuel pressure within the specified range? | 290-379 kPa (42-55 psi) | Go to Symptoms | Go to Step 9 | |||||||||||
9 |
Is the fuel pressure constant within the specified range? | 290-379 kPa (42-55 psi) | Go to Step 19 | Go to Step 20 | ||||||||||
10 |
Important:: Repeatedly pressurize the fuel system with the scan tool as necessary in order to achieve the highest possible fuel pressure. Does the fuel pressure remain constant? | -- | Go to Step 21 | Go to Step 11 | ||||||||||
11 |
Does the fuel pressure remain constant? | -- | Go to Step 20 | Go to Step 22 | ||||||||||
Is the fuel pressure more than the specified value? | 405 kPa (58 psi) | Go to Step 13 | Go to Step 15 | |||||||||||
Is the fuel pressure within the specified range? | 358-405 kPa (52-58 psi) | Go to Step 23 | Go to Step 14 | |||||||||||
14 | Visually and physically inspect the fuel rail outlet passages for a restriction. Was a restriction found? | -- | Go to Step 24 | Go to Step 20 | ||||||||||
Is the fuel pressure more than the specified value? | 0 kPa (0 psi) | Go to Step 16 | Go to Step 17 | |||||||||||
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Notice: Do not allow the fuel pressure to exceed the specified value because damage to the fuel pressure regulator or the fuel pressure gage may result.
Does the fuel pressure increase to more than the second specified value? | 490 kPa (71 psi) 405 kPa (58 psi) | Go to Step 20 | Go to Step 7 | |||||||||||
17 | Refer to Fuel Pump Electrical Circuit Diagnosis for fuel pump circuit diagnosis. Did you find and correct the condition? | -- | System OK | Go to Step 18 | ||||||||||
18 | Visually and physically inspect for the following conditions:
Did you find a problem in any of these areas? | -- | Go to Step 24 | Go to Step 21 | ||||||||||
19 | Locate and repair the loss of vacuum to the fuel pressure regulator. Did you find and complete the repair? | -- | System OK | -- | ||||||||||
20 | Replace the fuel pressure regulator. Refer to Fuel Pressure Regulator Replacement . Did you complete the repair? | -- | System OK | -- | ||||||||||
21 | Replace the modular fuel sender. Refer to Fuel Sender Assembly Replacement . Did you complete the repair? | -- | System OK | -- | ||||||||||
Locate and replace any leaking fuel injectors. Refer to Fuel Injector Replacement . Did you complete the repair? | -- | System OK | -- | |||||||||||
23 | Locate and correct the restriction in the fuel return pipe. Did you complete the repair? | -- | System OK | -- | ||||||||||
24 | Repair the problem as necessary. Did you complete the repair? | -- | System OK | -- |
