Fuel System Diagnosis without FFS
Circuit Description
When you turn on the ignition switch, the control module enables the fuel pump relay which powers the fuel pump ON. The fuel pump remains ON as long as the engine is cranking or running and the control module receives ignition reference pulses. If there are no ignition reference pulses, the control module shuts the fuel pump OFF within 2 seconds after the ignition was switched to the ON position or if the engine stops.
The electric fuel pump is attached to the fuel sender assembly inside the left fuel tank. The in-tank fuel pump supplies fuel through a fuel feed pipe, and a fuel filter/fuel pressure regulator assembly, to the fuel rail. The fuel pump supplies fuel to the siphon jet pump in the right fuel tank. The siphon jet pump transfers fuel from the right fuel tank to the left fuel tank. The fuel pump provides fuel at a pressure greater than that needed by the fuel injectors. The fuel pressure regulator, part of the fuel filter, keeps the fuel available to the fuel injectors at a regulated pressure. Unused fuel returns to the left 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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This step verifies that the vehicle is not out of fuel.
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This step tests for an internal fuel leak.
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This step tests for a loss of fuel pressure between the fuel feed pipe shut-off adapter and the fuel injectors.
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This step tests for a loss of fuel pressure between the fuel feed pipe shut-off adapter and the fuel pump.
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This step tests if the loss of fuel pressure is caused by the fuel pressure regulator, or by the check valve that is located in the fuel feed rear pipe.
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This step determines if the fuel pressure regulator, or the fuel pump is the cause of the low fuel pressure.
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This step verifies that there is an adequate supply of fuel to the siphon jet pump.
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This step verifies the auxiliary fuel return rear pipe is not restricted.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
System 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 damage or for external leaks before proceeding with this diagnostic.
Does the fuel pump operate? | -- | Go to Step 3 | |||||||||
3 | Observe the Fuel Level Sensor Left parameter with a scan tool. Is the Fuel Level Sensor Left parameter less than the specified value? | 0.8 V | Go to Step 4 | Go to Step 6 | ||||||||
Observe the Fuel Level Sensor Right parameter with a scan tool. Is the Fuel Level Sensor Right parameter less than the specified value? | 0.8 V | Go to Step 5 | Go to Step 16 | |||||||||
5 |
Does a driveability condition still exist? | 19 liters (5 gallons) | Go to Step 6 | Go to Step 29 | ||||||||
6 |
Important:
Is the fuel pressure within the specified value? | 380-427 kPa (55-62 psi) | Go to Step 7 | Go to Step 13 | ||||||||
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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 10 | Go to Step 8 | |||||||||
8 |
Does the fuel pressure decrease by more than the second specified value? | 69 kPa (10 psi) 14 kPa (2 psi) | Go to Step 28 | Go to Step 9 | ||||||||
9 |
Does the scan tool parameters indicate a lean condition? | -- | Go to Step 19 | |||||||||
Does the fuel pressure remain constant? | -- | Go to Step 11 | Go to Step 23 | |||||||||
Does the fuel pressure remain constant? | -- | Go to Step 28 | Go to Step 12 | |||||||||
Does the fuel pressure remain constant? | -- | Go to Step 25 | Go to Step 26 | |||||||||
13 | Is the fuel pressure above the specified value? | 427 kPa (62 psi) | Go to Step 14 | Go to Step 15 | ||||||||
14 | Inspect the fuel return rear pipe for a restriction. Refer to Fuel Hose/Pipes Routing Diagram . Did you find and correct the condition? | -- | Go to Step 29 | Go to Step 25 | ||||||||
Notice: DO NOT allow the fuel pressure to exceed 517 kPa (75 psi). Excessive pressure may damage the fuel system. Does the fuel pressure increase to more than the specified value? | 427 kPa (62 psi) | Go to Step 25 | Go to Step 20 | |||||||||
Important: DO NOT add more than 15 liters (4 gallons) of fuel. Important: You may need to command the fuel pump relay ON a few times in order to obtain the specified time limit. Is the volume of fuel greater than the specified value? | 10 seconds 300 ml (0.633 pt) | Go to Step 17 | Go to Step 24 | |||||||||
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Important: Inspect the crossover hose if the right fuel tank is empty. Fuel flow to the right fuel tank is decreased during fueling if the crossover hose is collapsed or restricted.
Is the volume of fuel greater than the specified value? | 8 seconds 332.6 ml (0.703 pt) | Go to Step 22 | Go to Step 18 | |||||||||
18 | Inspect the auxiliary fuel return rear pipe for a restriction. Did you find and correct the condition? | -- | Go to Step 29 | Go to Step 27 | ||||||||
19 | Inspect the following components for a restriction:
Did you find and correct the condition? | -- | Go to Step 29 | Go to Step 28 | ||||||||
20 | Inspect the harness connectors and 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 29 | Go to Step 21 | ||||||||
21 |
Did you find and correct the condition? | -- | Go to Step 29 | Go to Step 28 | ||||||||
22 | Repair the restriction in the left fuel sender assembly. Did you complete the repair? | -- | Go to Step 29 | -- | ||||||||
23 |
Did you complete the replacement? | -- | Go to Step 29 | -- | ||||||||
24 | Locate and repair the restriction in the following:
Did you complete the repair? | -- | Go to Step 29 | -- | ||||||||
25 | Replace the fuel filter/regulator assembly. Refer to Fuel Filter Replacement . Did you complete the replacement? | -- | Go to Step 29 | -- | ||||||||
26 | Replace the fuel feed rear pipe with the check valve. Refer to Fuel Hose/Pipes Assembly Replacement . Did you complete the action? | -- | Go to Step 29 | -- | ||||||||
27 | Replace the right fuel sender assembly. Refer to Fuel Sender Assembly Replacement . Did you complete the replacement? | -- | Go to Step 29 | -- | ||||||||
28 | Replace the left fuel sender assembly. Refer to Fuel Sender Assembly Replacement . Did you complete the replacement? | -- | Go to Step 29 | -- | ||||||||
29 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | Go to Step 3 | ||||||||
Fuel System Diagnosis with FFS
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 two 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.
Two fuel tanks store the fuel supply. An electric turbine style fuel pump attaches to the fuel sender assembly inside the left 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 left fuel sender assembly. The function of the Venturi pump is to fill the fuel sender assembly reservoir. The primary fuel pressure regulator, a part of the left 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, the primary fuel pressure regulator, and the secondary fuel pressure regulator maintain fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times.
The fuel pump also supplies a small amount of pressurized fuel through the auxiliary fuel feed pipe to the siphon jet pump inside the right fuel tank. The pressurized fuel creates a Venturi action inside the siphon jet pump. The Venturi action causes the fuel to be drawn out of the right fuel tank. The fuel transfers from the right fuel tank to the left fuel tank through the auxiliary fuel return pipe. The auxiliary fuel return pipe inside the left fuel tank contains an anti-siphon hole in order to prevent fuel from siphoning from the left fuel tank into the right fuel tank. Both the auxiliary fuel feed pipe and the auxiliary fuel return pipe are located inside the convoluted stainless steel crossover hose.
The right fuel sender assembly contains a secondary fuel pressure regulator. The secondary fuel pressure regulator has a lower set point than the primary regulator in order to allow fuel to flow to the siphon jet pump on the right fuel sender. When the engine is shut off, the pressure in the feed pipes immediately drops to the secondary regulator set point. This prevents the siphon jet pump from operating and in turn prevents the equalization of the left and right fuel tanks. The secondary fuel pressure regulator maintains fuel pressure in the auxiliary fuel feed pipe which reduces the time to prime the siphon jet pump. The pressurization also reduces fuel vaporization and boiling in the auxiliary fuel feed pipe.
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Schematic Reference: Fuel Hose/Pipes Routing Diagram | ||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||
2 | Observe the Fuel Level Sensor Left and Right parameters with a scan tool. Is the Fuel Level Sensor Left parameter less than the specified value? | 0.8 V | Go to Step 3 | Go to Step 4 | ||||
3 |
Important: Venting of fuel vapors during refueling is done through the fill limiter vent valve (FLVV) located on the right fuel tank. The fuel system may be difficult to fill if the Fuel Level Sensor Right parameter is more than 2.3 volts, indicating that the right fuel tank is full. The addition of fuel may be easier when done at a slow rate with a portable gasoline container. Add the specified amount of fuel. Did you complete the action? | 15 L (4 gal) | Go to Step 4 | -- | ||||
4 |
Important: Inspect the fuel system for damage or for external leaks before proceeding with this diagnostic.
Does the fuel pump operate? | -- | Go to Step 5 | |||||
5 |
Important: The engine coolant temperature must be below the operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling. Important: The fuel pump relay may need to be commanded ON a few times in order to obtain the highest possible fuel pressure. Is the fuel pressure within the specified value? | 380-427 kPa (55-62 psi) | Go to Step 6 | Go to Step 13 | ||||
6 |
Important: The fuel pressure will decrease when the fuel pump stops operating. After the fuel pump stops operating, the fuel pressure should stabilize and remain constant. Observe the J 34730-1A for 5 minutes. Does the fuel pressure decrease to less than the specified value? | 350 kPa (51 psi) | Go to Step 12 | Go to Step 7 | ||||
7 | Observe the Fuel Level Sensor Right parameter. Is the Fuel Level Sensor Right parameter less than the specified value? | 1 V | Go to Step 8 | Go to Step 10 | ||||
8 | Fill the fuel system until the Fuel Level Sensor Right parameter is more than the specified value. Did you complete the action? | 1 V | Go to Step 9 | -- | ||||
9 | Drain the left fuel tank until the Fuel Level Sensor Left parameter is less than the specified value. Refer to Fuel Tank Draining . Did you complete the action? | 1.5 V | Go to Step 10 | -- | ||||
10 |
Does the Fuel Level Sensor Right parameter decrease while the Fuel Level Sensor Left parameter increases? | -- | Go to Step 11 | Go to Step 15 | ||||
11 |
Do the scan tool parameters indicate a lean condition? | -- | Go to Step 14 | |||||
12 |
Does the fuel pressure remain constant? | -- | Go to Step 15 | Go to Step 22 | ||||
13 | Is the fuel pressure more than the specified value? | 427 kPa (62 psi) | Go to Step 23 | Go to Step 14 | ||||
14 | Inspect the following components for a restriction:
Did you find and correct the condition? | -- | Go to Step 26 | Go to Step 15 | ||||
15 |
Does the flow meter indicate a leak? | -- | Go to Step 25 | Go to Step 16 | ||||
16 |
Does the flow meter indicate a leak? | -- | Go to Step 25 | Go to Step 17 | ||||
17 | Inspect for damaged O-rings at the crossover hose to fuel tank connections. Did you find and correct the condition? | -- | Go to Step 26 | Go to Step 18 | ||||
18 |
Does the flow meter indicate a leak? | -- | Go to Step 21 | Go to Step 19 | ||||
19 |
Does the flow meter indicate a leak? | -- | Go to Step 20 | Go to Step 23 | ||||
20 |
Did you find and correct the condition? | -- | Go to Step 26 | Go to Step 23 | ||||
21 |
Did you find and correct the condition? | -- | Go to Step 26 | Go to Step 24 | ||||
22 |
Did you complete the replacement? | -- | Go to Step 26 | -- | ||||
23 | Replace the left fuel sender assembly. Refer to Fuel Sender Assembly Replacement . Did you complete the replacement? | -- | Go to Step 26 | -- | ||||
24 | Replace the right fuel sender assembly. Refer to Fuel Sender Assembly Replacement . Did you complete the replacement? | -- | Go to Step 26 | -- | ||||
25 | Replace the fuel tank crossover tube/hose. Refer to Fuel Tank Crossover Tube Replacement . Did you complete the replacement? | -- | Go to Step 26 | -- | ||||
26 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | Go to Step 5 | ||||
