Fuel System Diagnosis. Chevrolet Cavalier 1996

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1996 🢒 Cavalier 🢒 Engine 🢒 Engine Controls - 2.4L 🢒 Fuel System Diagnosis


(1)	Flexible Hose
(2)	Fuel Hose Pinch Point
(3)	Return Line
(4)	Pressure Line
(5)	Bleed Hose
(6)	Fuel Hose Pinch Point
(7)	Fuel Hose Pinch Point
(8)	Fuel Pressure Gauge Kit J 29658-D
(9)	Quick-Connect Adapters

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 the in-tank fuel pump OFF 2 seconds after the ignition switch is turned ON or 2 seconds after 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 passage within the lower manifold assembly. The fuel pump is designed to provide fuel at a pressure above the pressure needed by the fuel injectors. A fuel pressure regulator, attached to the lower manifold assembly, keeps the fuel available to the fuel injectors at a regulated pressure. Unused fuel is returned to the fuel tank by a separate fuel return pipe.

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

To relieve the fuel pressure, refer to Fuel Pressure Relief Procedure When the ignition switch is ON and the fuel pump is running, the fuel pressure indicated by the fuel pressure gage should be 284-325 kPa (41-47 psi). This pressure is controlled by the amount of pressure the spring inside the fuel pressure regulator can provide.

A fuel system that can not maintain a constant fuel pressure 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).

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 sensors will stop toggling. The oxygen sensor output voltage(s) will drop below 500 mV. Also, the fuel injector width will increase.

Important: Make sure the fuel system is not operating in the Fuel Cut-Off Mode . This can cause false indications by the scan tool.

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.

A rich condition may result from the fuel pressure being above 325 kPa (47 psi). A rich condition may 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.

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.

A lean condition may result from the fuel pressure being below 284 kPa (41 psi). 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), hesitation, poor driveability, lack of power, surging, and misfiring.

Restricting the fuel return pipe causes the fuel pressure to rise above the regulated fuel pressure. Using a scan tool to pressurize the system, the fuel pressure should rise above 325 kPa (47 psi) as the gage outlet hose is pinched.

Check the spark plug associated with a particular fuel injector for fouling or saturation in order to determine if that particular fuel injector is leaking.

The fuel pressure regulator filter screen is designed to trap any contaminants introduced during engine assembly. If the fuel pressure regulator screen is dirty, it can be removed with a small pick and discarded without potential harm to the fuel pressure regulator.

Table A-7- Fuel System Diagnosis

Step

Action

Value(s)

Yes

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Turn the ignition OFF.
Turn the air conditioning system OFF.
Relieve the fuel pressure. Refer to the Fuel Pressure Relief Procedure .
Install fuel pressure gage. Refer to illustration.
Turn the ignition ON.
Bleed the air out of the fuel pressure gage into an approved gasoline container.
Turn the ignition OFF for 10 seconds.
Turn the ignition ON.

Important: The fuel pump will run for approximately 2 seconds. Cycle the ignition as necessary in order to achieve the highest possible fuel level

Observe the fuel pressure indicated by the fuel pressure gage with the fuel pump running.

Is the fuel pressure within the specified limits?

284-325 kPa (41-47 psi)

Go to Step 3

Go to Step 11

Important: The fuel pressure may vary slightly when the fuel pump stops running, the fuel pressure should stabilize and remain constant.

After the fuel pump stops running, does the fuel pressure remain constant?

Go to Step 4

Go to Step 9

Is the fuel pressure suspected of dropping-off during acceleration, cruise, or hard cornering.

Go to Step 5

Go to Step 7

Visually and physically inspect the following items for a restriction:

•	The in-line fuel filter.

•	The fuel feed pipe.

Was a restriction found?

Go to Step 25

Go to Step 6

Remove the modular sender assembly. Refer to Fuel Sender Assembly Replacement
Visually and physically inspect the following items:

•	The fuel pump strainer for a restriction.

•	The fuel pump flex pipe for leaks.

•	Verify the fuel pump is the correct fuel pump for this vehicle.

•	The fuel pump electrical wiring for high resistance.

Was a problem found in any of these areas?

Go to Step 25

Go to Step 21

Start the engine.
Allow the engine to idle at normal operating temperature.

Does the fuel pressure drop by the amount specified?

21-69 kPa (3-10 psi)

Go to Symptoms

Go to Step 8

Disconnect the vacuum hose from the fuel pressure regulator.
With the engine idling, apply 12-14 inches of vacuum to the fuel pressure regulator.

Does the fuel pressure indicated by the fuel pressure gage drop by the amount specified?

21-6 kPa (3-10 psi)

Go to Step 19

Go to Step 20

Turn the ignition OFF.
Place the bleed hose of the fuel pressure gage into an approved gasoline container.
Turn the ignition ON.
Bleed the air out of the fuel pressure gage.
Using a scan tool pressurize the fuel system.

Important: The fuel pump will run for approximately 2 seconds. Repeat Step 5 as necessary in order to achieve the highest possible fuel pressure.

Wait for the fuel pressure to build.
Pinch the gage inlet hose (refer to 6 on illustration).

Does the fuel pressure remain constant?

Go to Step 21

Go to Step 10

Using a scan tool pressurize the fuel system.
Wait for the fuel pressure to build.
Pinch the fuel return hose (refer to 2 on illustration).

Does the fuel pressure indicated by the fuel pressure gage remain constant?

Go to Step 20

Go to Step 22

Is the fuel pressure above the specified limit?

325 kPa (47 psi)

Go to Step 12

Go to Step 15

Relieve the fuel pressure by placing the bleed hose of the fuel pressure gage into an approved gasoline container and opening the relief valve.
Disconnect the fuel return hose quick-connect fitting, refer toServicing Quick Connect Fittings
Place the open end of the flexible hose into an approved gasoline container.
Turn the ignition OFF for approximately 10 seconds.
Turn the ignition ON.
Observe the fuel pressure gage with the fuel pump running.

Is the fuel pressure within the specified limits?

284-325 kPa (41-47 psi)

Go to Step 23

Go to Step 13

Visually and physically inspect the fuel outlet passages for a restriction.

Was a restriction found?

Go to Step 25

Go to Step 14

Remove the fuel pressure regulator. Refer to Fuel Pressure Regulator Replacement

Visually and physical inspect the fuel pressure regulator filter screen for a restriction.

Was a restriction found?

Go to Step 24

Go to Step 20

Is the fuel pressure above the specified value?

0 kPa (0 psi)

Go to Step 16

Go to Step 17

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.

Relieve the fuel pressure by placing the bleed hose of the fuel pressure gage into an approved gasoline container and opening the relief valve.

Important:: The fuel pump will run for approximately 2 seconds. Repeat Step 2 as necessary in order to achieve the highest possible fuel pressure.