Schematic Reference: Engine Controls Schematics
Circuit Description
When the ignition switch is turned to the "START" position, the circuit opening relay will be energized to allow the fuel pump to operate and pressurize the system. The fuel pump will continue to operate if the Engine Control Module (ECM) receives an ignition signal when the engine is started. The fuel pump operates as long as the circuit opening relay is energized by the ECM. When the circuit opening relay is de-energized, the fuel pump will stop operating. The fuel pump delivers fuel to the fuel rail where the pressure is maintained by the fuel pressure regulator at 284 kPa (41 psi) higher than the pressure inside the intake manifold. Excess fuel is returned to the fuel tank through a return pipe and hoses.
Diagnostic Aids
Check for leakage around all fuel hose/pipe connections. A plugged fuel injector could be the cause of a hard/no-start condition or loss of power/poor fuel economy. Refer to Symptoms for mechanical checks and inspections if fuel spray and pressure is normal.
Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
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The OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
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To relieve the fuel pressure, refer to the Fuel Pressure Relief Procedure. With terminals "Fp" and +B jumpered and the ignition switch "ON" with the fuel pump running, the fuel pressure indicated by the fuel pressure gauge should be 265-304 kPa (38-44 psi). This pressure is controlled by the amount of pressure the spring inside the fuel pressure regulator can provide.
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A fuel system that can not maintain a constant fuel pressure if it has a leak in one or more of the following areas:
| • | The Fuel Pump Check Valve. |
| • | The Fuel Pump Flex Pipe. |
| • | The Valve or Valve Seat within the Fuel Pressure Regulator. |
| • | The Fuel Injector(s). |
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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 misfire. A lean condition can be diagnosed using a scan tool. If an extremely lean condition occurs, the Oxygen Sensor(s) 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 at idle, 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 fuel pressure regulator. When this happens, the result is 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 "OFF".
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A rich condition may result from the fuel pressure being above 325 kPa (47 psi). A rich condition may cause a DTC P0130 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 faulty fuel pressure regulator.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Was the Engine On-Board Diagnostic (OBD) System Check performed? | -- | |||||||||||
Is the fuel pressure within the specified limits? | 265-304 kPa (38-44 psi) | |||||||||||
Does the fuel pressure indicated by the fuel pressure gauge remain constant? | -- | |||||||||||
Is the fuel pressure suspected of dropping-off during acceleration, cruise, or hard cornering? | -- | |||||||||||
5 | Visually and physically inspect the following items for a restriction:
Was a restriction found? | -- | ||||||||||
6 | Repair the restriction as necessary. Is the action complete? | -- | -- | |||||||||
7 | Visually and physically inspect the following items:
Was a problem found in any of these areas? | -- | ||||||||||
8 | Repair the condition as necessary. Is the action complete? | -- | -- | |||||||||
9 | Replace the fuel pump. Is the action complete? | -- | -- | |||||||||
10 |
Does the fuel pressure indicted by the fuel pressure gauge drop by the amount specified? | 21-69 kPa (3-10 psi) | Go to Symptoms | |||||||||
Does the fuel pressure indicated by the fuel pressure gauge drop by the amount specified? | 21-69 kPa (3-10 psi) | |||||||||||
12 | Locate and repair the loss of vacuum to the fuel pressure regulator. Is the action complete? | -- | -- | |||||||||
13 | Replace the fuel pressure regulator. Is the action complete? | -- | -- | |||||||||
14 |
Does the fuel pressure indicated by the fuel pressure gauge remain constant? | -- | ||||||||||
15 | Visually and physically inspect the fuel feed pipe for leakage, between the fuel rail and fuel pump. Is the fuel feed pipe leaking? | -- | ||||||||||
16 | Repair the fuel feed pipe. Is the action complete? | -- | -- | |||||||||
17 |
Does the fuel pressure indicated by the fuel pressure gauge remain constant? | -- | ||||||||||
18 | Replace the fuel pressure regulator. Is the action complete? | -- | -- | |||||||||
19 | Locate and replace any leaking fuel injector(s). Is the action complete? | -- | -- | |||||||||
Is the fuel pressure indicated by the fuel pressure gauge above the specified limit? | 304 kPa (44 psi) | |||||||||||
21 |
Is the fuel pressure within the specified limits? | 265-30 kPa (38-44 psi) | ||||||||||
22 | Locate and correct the restriction in the fuel return pipe. Is the action complete? | -- | -- | |||||||||
23 | Visually and physically inspect the fuel rail outlet passages for the restriction. Was a restriction found? | -- | ||||||||||
24 | Is the fuel pressure indicated by the fuel pressure gauge above the specified value? | 0 kPa (0 psi) | ||||||||||
25 |
Do not let the fuel pressure exceed the specified value. Does the fuel pressure indicated by the fuel pressure gauge rise above the specified value? | 305 kPa (45 psi) | ||||||||||
26 | Use Chart A-7A table to diagnose the fuel pump electrical circuit. Was a problem found with the fuel pump electrical circuit? | -- | ||||||||||
27 | Visually and physically inspect the following items:
Was a problem found in any of these areas? | -- | ||||||||||
28 | Repair the problem as necessary. Is the action complete? | -- | -- | |||||||||
29 |
Is the fuel pressure within the specified limits? | 265-304 kPa (38-44 psi) | ||||||||||
30 | Does the fuel pressure indicated by the fuel pressure gauge remain constant? | -- | ||||||||||
31 |
Does the engine start and continue to run? | -- | ||||||||||
32 |
Are any DTCs displayed? | -- | Go to Applicable DTC Table | System OK |
