Refer to Engine Controls Component Views
Fuel System with Fuel Pressure Gauge Kit
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 since the ignition switch is turned ON or after 2 seconds once 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 the step numbers on the diagnostic table.
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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 voltage(s) will drop below 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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Fuel pressure being below 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, poor 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 above 405 kPa (58 psi) as the gauge outlet hose is pinched.
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Check the spark plug that is associated with a particular fuel injector for fouling or saturation in order to determine if that particular fuel injector is leaking.
| • | The fuel pump check valve |
| • | The fuel pump flex pipe |
| • | The fuel injector(s) |
Step | Action | Value(s) | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||||
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 limits? | 358-405 kPa (52-58 psi) | |||||||||||||
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Important: The fuel pressure may vary slightly when the fuel pump stops running. Then, the fuel pressure should stabilize and then remain constant. Observe the fuel pressure after the fuel pump stops running. Does the fuel pressure drop more than the specified value in 10 minutes? | 34 kPa (5 psi) | |||||||||||||
4 |
Does the fuel pressure drop more than the second specified value in 10 minutes? | 69 kPa (10 psi) 14 kPa (2 psi) | ||||||||||||
Is the fuel pressure suspected of dropping-off during acceleration, during cruise, or during hard cornering? | -- | |||||||||||||
6 | Visually and physically inspect the following items for a restriction:
Was a restriction found? | -- | ||||||||||||
7 |
Was a problem found in any of these areas? | -- | ||||||||||||
Is the fuel pressure within the specified limits? | 290-379 kPa (42-55 psi) | System OK, Go to Symptoms | ||||||||||||
9 |
Is the fuel pressure within the specified limits and remain constant? | 290-379 kPa (42-55 psi) | ||||||||||||
10 |
Important:: Repeat pressurizing the fuel system with the scan tool as necessary to achieve the highest possible fuel pressure. Does the fuel pressure remain constant? | -- | ||||||||||||
11 |
Does the fuel pressure indicated by the fuel pressure gauge remain constant? | -- | ||||||||||||
Is the fuel pressure above the specified limit? | 405 kPa (58 psi) | |||||||||||||
Is the fuel pressure within the specified limits? | 358-405 kPa (52-58 psi) | |||||||||||||
14 | Visually and physically inspect the fuel rail outlet passages for a restriction. Was a restriction found? | -- | ||||||||||||
Is the fuel pressure above the specified value? | 0 kPa (0 psi) | |||||||||||||
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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 indicated by the fuel pressure gauge rise above the first specified value? | 405 kPa (58 psi) 490 kPa (71 psi) | |||||||||||||
17 | Refer to Fuel Pump Electrical Circuit Diagnosis in order to diagnose the fuel pump electrical circuit. Was a problem found with the fuel pump electrical circuit? | -- | ||||||||||||
18 | Visually and physically inspect the following items:
Was a problem found in any of these areas? | -- | ||||||||||||
19 | Locate and repair the loss of vacuum to the fuel pressure regulator. Is the action complete? | -- | System OK | -- | ||||||||||
20 | Replace the fuel pressure regulator. Refer to Fuel Pressure Regulator Replacement . Is the action complete? | -- | System OK | -- | ||||||||||
21 | Replace the modular fuel sender. Refer to Fuel Sender Assembly Replacement . Is the action complete? | -- | System OK | -- | ||||||||||
Locate and replace any leaking fuel injector(s). Refer to Fuel Injector Replacement . Is the action complete? | -- | System OK | -- | |||||||||||
23 | Locate and correct the restriction in the fuel return pipe. Is the action complete? | -- | System OK | -- | ||||||||||
24 | Repair the problem as necessary. Is the action complete? | -- | System OK | -- |
