Circuit Description
When you turn ON the ignition switch, the Vehicle Control Module (VCM) turns ON the in-tank fuel pump. The pump remains ON as long as the engine is cranking or running and the VCM is receiving reference pulses. If there are no reference pulses, the VCM shuts the fuel pump OFF within 2 seconds after the ignition was switched to the ON position or if the engine stops. The VCM will also turn ON the fuel pump for 2 seconds when the ignition is turned to the OFF position.
An electric fuel pump pumps the fuel through an in-line filter to the Central SFI unit. The pump is attached to the fuel level meter assembly inside of the fuel tank. The pump is designed to provide fuel pressure above what is needed by the fuel injectors. The pressure regulator keeps the fuel available to the injectors at a regulated pressure. Unused fuel is returned to the fuel tank by the fuel return pipe.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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Wrap a shop towel around the fuel pressure connection to absorb any small amount of fuel leakage that may occur when installing the fuel pressure gauge. Turn ON the ignition leaving the engine OFF, the fuel pressure should be 415-455 kPa (60-66 psi) when the pump is running. This pressure is controlled by a spring pressure within the regulator assembly.
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The fuel pressure that continues to fall is caused by one of the following items:
| • | The in-tank modular fuel sender is not holding pressure. |
| • | The fuel pressure regulator valve is leaking. |
| • | A Central SFI injector is leaking. |
| • | Fuel line is leaking. |
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If the fuel pressure is less than 379 kPa (55 psi) at idle, it falls into the following 3 areas:
| • | The pressure is regulated but less than 379 kPa (55 psi).The amount of fuel reaching the injector is sufficient, but the pressure is too low. The system will run lean, hard starting cold, no start, overall poor performance, and may set a DTC. Refer to Engine Cranks but Does Not Run . |
| • | A restricted flow causing pressure drop -- Normally, a vehicle with a fuel pressure of less than 300 kPa (44 psi) at idle is inoperable. However, if the pressure drop occurs only while driving, the engine will normally surge then stop running as the pressure begins to drop rapidly. This is most likely caused by a restricted fuel line or plugged filter. |
| • | A leaking or contaminated pressure regulator valve or seat interface may not allow the regulated pressure to be achieved. |
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Notice: DO NOT allow the fuel pressure to exceed 517 kPa (75 psi). Excessive pressure may damage the fuel system.
Restricting the fuel return line allows the fuel pressure to build above regulated pressure. With the fuel pump commanded ON, the fuel pressure should rise above 455 kPa (66 psi), as the valve in the return line is partially closed.
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When the engine is idling, the manifold pressure is low (high vacuum) and is applied to the fuel pressure regulator diaphragm. This will offset the spring and result in a lower fuel pressure. This idle pressure will vary somewhat depending on the barometric pressure; however, the pressure at idle should be less indicating the pressure regulator control.
Step | Action | Values | Yes | No | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||||||
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Caution: The fuel pump will operate for 2 seconds after you have turned off the ignition. Make sure that all the fuel pipes and fittings are securely fastened in order to prevent personal injury.
Caution: Wrap a shop towel around the fuel pressure connection in order to reduce the risk of fire and personal injury. The towel will absorb any fuel leakage that occurs during the connection of the fuel pressure gage. Place the towel in an approved container when the connection of the fuel pressure gage is complete. Important: The fuel pump may have to be commanded ON more than once in order to obtain the maximum fuel pressure. Is the fuel pressure within the specified value? | Central SFI - 413-455 kPa (60-66 psi) | |||||||||||||||
3 | Using the scan tool, command the fuel pump ON. After the pump stops, does the fuel pressure hold steady within the specified value? | Central SFI - 379-413 kPa (55-60 psi) | ||||||||||||||
Caution: Place a dry chemical (Class B) fire extinguisher nearby before performing any on-vehicle service procedures. Failure to follow these precautions may result in personal injury. Caution: Provide proper ventilation when working with fuel in enclosed areas where fuel vapors can collect. The lack of adequate ventilation may result in personal injury. Does the fuel pressure remain constant within the specified value? | Central SFI - 379-413 kPa (55-60 psi) | |||||||||||||||
5 | Is the fuel pressure suspected of dropping-off during acceleration, cruise, or hard cornering? | -- | ||||||||||||||
6 | Inspect the fuel feed line between the shut-off adapter and the engine fuel pipes. Was a problem found? | -- | ||||||||||||||
7 |
Caution: Place a dry chemical (Class B) fire extinguisher nearby before performing any on-vehicle service procedures. Failure to follow these precautions may result in personal injury. Caution: Provide proper ventilation when working with fuel in enclosed areas where fuel vapors can collect. The lack of adequate ventilation may result in personal injury. Does the fuel pressure remain constant? | -- | ||||||||||||||
8 |
Is the fuel pressure present? | -- | ||||||||||||||
9 |
Does the fuel pump run? | -- | ||||||||||||||
10 | Check for the following conditions:
Was a problem found? | -- | ||||||||||||||
11 | Repair or replace as necessary. Is the action complete? | -- | -- | |||||||||||||
12 | Check for a leaking fuel feed pipe in between the shut-off adapter and the modular fuel sender, if no leak is present, replace the modular fuel sender. Refer to Fuel Sender Assembly Replacement . Is the action complete? | -- | -- | |||||||||||||
13 |
Is the fuel pressure above the specified value? | Central SFI - 455 kPa (66 psi) | ||||||||||||||
14 |
Caution: Place a dry chemical (Class B) fire extinguisher nearby before performing any on-vehicle service procedures. Failure to follow these precautions may result in personal injury. Caution: Provide proper ventilation when working with fuel in enclosed areas where fuel vapors can collect. The lack of adequate ventilation may result in personal injury. Is the fuel pressure within the specified value while the pump is running? | Central SFI - 413-455 kPa (60-66 psi) | ||||||||||||||
Is the fuel pressure below the specified value? | Central SFI - 413 kPa (60 psi) | |||||||||||||||
16 | Locate and correct the restriction in the fuel return line. Is the action complete? | -- | ||||||||||||||
17 | Visually and physically inspect the engine fuel return outlet pipe (where the fuel line was disconnected) for restriction. Was a restriction found? | -- | ||||||||||||||
18 | Replace the engine fuel pipes. Refer to Fuel Hose/Pipes Replacement - Engine Compartment . Is the action complete? | -- | -- | |||||||||||||
19 | Perform the following items:
Was a problem found? | -- | ||||||||||||||
20 | Repair or replace as necessary the following items:
Is the action complete? | -- | -- | |||||||||||||
Caution: Place a dry chemical (Class B) fire extinguisher nearby before performing any on-vehicle service procedures. Failure to follow these precautions may result in personal injury. Caution: Provide proper ventilation when working with fuel in enclosed areas where fuel vapors can collect. The lack of adequate ventilation may result in personal injury. Notice: DO NOT allow the fuel pressure to exceed 517 kPa (75 psi). Excessive pressure may damage the fuel system. Does the fuel pressure rise above the specified value? | Central SFI - 455 kPa (66 psi) | |||||||||||||||
22 | Replace the fuel pressure regulator. Refer to Fuel Pressure Regulator Replacement . Is the action complete? | -- | -- | |||||||||||||
23 | Perform the following items:
Was a problem found? | -- | ||||||||||||||
24 | Repair or replace as necessary. Is the action complete? | -- | -- | |||||||||||||
25 | Replace the fuel feed line. Is the action complete? | -- | -- | |||||||||||||
Does the fuel pressure rise quickly? | Central SFI - 413-455 kPa (60-66 psi) | Go to Driveability Symptoms | ||||||||||||||
27 | Visually and physically inspect the following items for a restriction:
Was a problem found in any of these areas? | -- | ||||||||||||||
28 | Repair the problem as necessary. Is the action complete? | -- | -- | |||||||||||||
Locate and replace any leaking or grounded injectors. Refer to Test Description for this step. For grounded injector diagnosis, refer to Fuel Injector Circuit Diagnosis . Is the action complete? | -- | |||||||||||||||
30 | Use the scan tool in order to display the Capture Information and the Review Capture Information function. Are there any DTCs displayed that have not been diagnosed? | -- | Go to the applicable DTC table | System OK |
