Fuel System Diagnosis With Returnless Fuel System
System Description
The control module enables the fuel pump relay when the ignition switch is turned ON. The control module will disable the fuel pump relay within 2 seconds unless the control module detects ignition reference pulses. The control module continues to enable the fuel pump relay as long as ignition reference pulses are detected. The control module disables the fuel pump relay within 2 seconds if ignition reference pulses cease to be detected and the ignition remains ON.
The fuel system is a returnless on-demand design. The fuel pressure regulator is a part of the fuel sender assembly, eliminating the need for a return pipe from the engine. A returnless fuel system reduces the internal temperature of the fuel tank by not returning hot fuel from the engine to the fuel tank. Reducing the internal temperature of the fuel tank results in lower evaporative emissions.
The fuel tank stores the fuel supply. An electric turbine style fuel pump attaches to the fuel sender assembly inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter and the fuel feed pipe to the fuel injection system. The fuel pump provides fuel at a higher rate of flow than is needed by the fuel injection system. The fuel pump also supplies fuel to a venturi pump located on the bottom of the fuel sender assembly. The function of the venturi pump is to fill the fuel sender assembly reservoir. The fuel pressure regulator, a part of the fuel sender assembly, maintains the correct fuel pressure to the fuel injection system. The fuel pump and sender assembly contains a reverse flow check valve. The check valve and the fuel pressure regulator maintain fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times.
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Schematic Reference: Fuel Hose/Pipes Routing Diagram | ||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||
2 |
Important: Inspect the fuel system for external leaks before proceeding with this diagnostic.
Does the fuel pump operate? | -- | Go to Step 3 | |||||
3 |
Important: Verify that adequate fuel is in the fuel tank before proceeding with this diagnostic.
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:
Is the fuel pressure within the specified range? | 385-425 kPa (55-62 psi) | Go to Step 4 | Go to Step 8 | ||||
4 |
Important: The fuel pressure may vary slightly when the fuel pump stops operating. After the fuel pump stops operating, the fuel pressure should stabilize and remain constant. Monitor the fuel pressure gage for 1 minute. Does the fuel pressure decrease by more than the specified value? | 34 kPa (5 psi) | Go to Step 7 | Go to Step 5 | ||||
5 |
Does the fuel pressure decrease by more than the second specified value? | 69 kPa (10 psi) 14 kPa (2 psi) | Go to Step 12 | Go to Step 6 | ||||
6 |
Does the scan tool parameters indicate a lean condition? | -- | Go to Step 9 | |||||
7 |
Does the fuel pressure remain constant? | -- | Go to Step 12 | Go to Step 11 | ||||
8 | Is the fuel pressure more than the specified value? | 427 kPa (62 psi) | Go to Step 12 | Go to Step 9 | ||||
9 | Inspect the fuel feed pipe for a restriction. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 | ||||
10 | Inspect the harness connectors and the ground circuits of the fuel pump for poor connections. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12 | ||||
11 |
Did you complete the replacement? | -- | Go to Step 13 | -- | ||||
12 | Replace the fuel sender. Refer to Fuel Sender Assembly Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- | ||||
13 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | Go to Step 3 | ||||
Fuel System Diagnosis Without Returnless Fuel System
System Description
The control module enables the fuel pump relay when the ignition switch is turned ON. The control module will disable the fuel pump relay within two seconds unless the control module detects ignition reference pulses. The control module continues to enable the fuel pump relay as long as ignition reference pulses are detected. The control module disables the fuel pump relay within two seconds if ignition reference pulses cease to be detected and the ignition remains ON.
The fuel tank stores the fuel supply. The electric fuel pump supplies fuel through an in-line fuel filter to the fuel injection system. The pump provides fuel at a higher rate of flow than is needed by the fuel injection system. The fuel pressure regulator maintains the correct fuel pressure to the fuel injection system. A separate pipe returns unused fuel to the fuel tank.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests for an internal fuel leak.
-
This step tests the fuel pump check valve for a leak down condition.
-
This step tests the fuel pressure regulator.
-
This step tests for a loss of fuel pressure between the fuel feed pipe shut-off adapter and the fuel pump.
-
This step tests for a leaking fuel injector or for a leaking fuel pressure regulator.
-
This step tests for a restricted fuel return pipe.
-
This step determines if the fuel pressure regulator or the fuel pump is the cause of the low fuel pressure.
-
This step verifies that a circuit condition is not the cause of a fuel pressure concern.
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Fuel Hose/Pipes Routing Diagram | ||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||
2 |
Important: Before you proceed with this diagnostic, inspect the fuel system for damage and for external leaks.
Does the fuel pump turn ON when commanded with a scan tool? | Go to Step 3 | Go to Intermittent Conditions | |||||||||
3 |
Important: Before you proceed with this diagnostic, inspect the fuel system for damage and for external leaks.
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:
Is the fuel pressure within the specified value? | 380-427 kPa (55-62 psi) | Go to Step 4 | Go to Step 12 | ||||||||
|
Important: The fuel pressure may vary slightly when the fuel pump stops operating. After the fuel pump stops operating, the fuel pressure should stabilize, then remain constant. Observe the fuel pressure gage for 1 minute. Does the fuel pressure drop more than the specified value? | 34 kPa (5 psi) | Go to Step 9 | Go to Step 5 | |||||||||
Does the fuel pressure drop more than the second specified value? | 69 kPa (10 psi) 14 kPa (2 psi) | Go to Step 24 | Go to Step 6 | |||||||||
Does the fuel pressure drop the specified value when the engine is started? | 21-69 kPa (3-10 psi) | Go to Step 7 | Go to Step 8 | |||||||||
7 |
Do any of the scan tool parameters indicate a lean condition? | -- | Go to Step 17 | |||||||||
8 |
Does the fuel pressure drop the specified value when the vacuum is applied? | 21-69 kPa (3-10 psi) | Go to Step 21 | Go to Step 23 | ||||||||
9 |
Is the fuel pressure regulator leaking fuel? | -- | Go to Step 23 | Go to Step 10 | ||||||||
Does the fuel pressure remain constant? | -- | Go to Step 19 | Go to Step 11 | |||||||||
Does the fuel pressure remain constant? | -- | Go to Step 23 | Go to Step 20 | |||||||||
12 | Is the fuel pressure more than the specified value? | 427 kPa (62 psi) | Go to Step 14 | Go to Step 13 | ||||||||
13 | Is the fuel pressure more than the specified value? | 0 kPa (0 psi) | Go to Step 16 | Go to Step 17 | ||||||||
Is the fuel pressure within the specified value? | 380-427 kPa (55-62 psi) | Go to Step 22 | Go to Step 15 | |||||||||
15 | Inspect the fuel rail outlet passage for a restriction. Did you find and correct the condition? | -- | Go to Step 25 | Go to Step 23 | ||||||||
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? | 427 kPa (62 psi) | Go to Step 23 | Go to Step 17 | |||||||||
17 | Inspect the following components for restrictions:
Did you find and correct the condition? | -- | Go to Step 25 | Go to Step 18 | ||||||||
Test for an intermittent and for a poor connection at the harness connectors and the ground circuits of the fuel pump. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 25 | Go to Step 19 | |||||||||
19 |
Did you find and correct the condition? | -- | Go to Step 25 | Go to Step 24 | ||||||||
20 |
Did you complete the replacement? | -- | Go to Step 25 | -- | ||||||||
21 | Repair the vacuum source to the fuel pressure regulator. Did you complete the repair? | -- | Go to Step 25 | -- | ||||||||
22 | Locate and repair the restricted fuel return line. Did you complete the repair? | -- | Go to Step 25 | -- | ||||||||
23 |
Important: Before your replace the fuel pressure regulator, inspect for a missing or damaged fuel pressure regulator O-ring seal. Replace the fuel pressure regulator. Refer to Fuel Pressure Regulator Replacement . Did you complete the replacement? | -- | Go to Step 25 | -- | ||||||||
24 | Replace the fuel pump. Refer to Fuel Sender Assembly Replacement . Did you complete the replacement? | -- | Go to Step 25 | -- | ||||||||
25 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | Go to Step 3 | ||||||||
