Fuel System Pressure Test. Cadillac DeVille 1996

For 1990-2009 cars only

Makes 🢒 Cadillac 🢒 1996 🢒 DeVille 🢒 Engine 🢒 Engine Controls - 4.0L and 4.6L 🢒 Fuel System Pressure Test


(1)	Fuel Feed Pipe
(2)	In-Line Fuel Filter
(3)	Fuel Return Pipe
(4)	Fuel Pump Flex Pipe
(5)	Integral Reservoir
(6)	Fuel Pipe Shut-off Adapters
(7)	Fuel Pressure Guage
(8)	Fuel Pressure Connection
(9)	Fuel Rail
(10)	Fuel Pressure Regulator

Refer to

Fuel Injectors

Engine Controls Components
IAT/ ECT/ TP/ MAP and BBV Sensors
Fuel Pump and Relay
OBD II Symbol Description Notice
ESD Notice
for an electrical diagram of this circuit.

The Fuel Pressure Check determines if the fuel system is providing fuel pressure. The components involved include the fuel tank, sending unit, pump, pipes and hoses, pressure regulator, fuel rail, and injectors. Also checked is the electrical operation of the fuel pump relay. This chart requires J 34730-1A , Fuel Pressure Gauge J 37287 , Inlet and Return Fuel Line Shut-off Adapters.

Test Description

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

With the ignition switch ON and the fuel pump running, the fuel pressure indicated by the fuel pressure gauge should be 333-376 kPa (48-55 psi). This pressure is controlled by the amount of pressure the spring inside the fuel pressure regulator can provide.

A fuel system that drops more than 5 psi in 10 minutes has a leak in one or more of the following areas:

•	The Fuel Pump Check Valve.

•	The Fuel Pump Flex Pipe.

•	The Fuel Pressure Regulator.

•	The Fuel Injector(s).

Fuel pressure that drops-off during acceleration, cruise, or hard cornering can cause a lean condition. A lean condition can cause loss of power, surging, or misfire. A lean condition can be diagnosed using a scan tool.

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 not running.

A rich condition may result from the fuel pressure being above 376 kPa (55 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 333 kPa (48 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.

Notice:: Do not allow the fuel pressure to exceed 414 kPa (60 psi). Fuel Pressure in excess of 414 kPa (60 psi) may damage the fuel pressure regulator.

Restricting the Fuel Return Pipe with the J 37287 Fuel Pipe Shut-Off Adapter 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 376 kPa (55 psi) as the valve on the Fuel Pipe Shut-Off Adapter connected to the Fuel Return Pipe becomes partially closed.

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. If checking the spark plug associated with a particular fuel injector for fouling or saturation does not determine that a particular fuel Injector is leaking, use the following procedure:

Step

Action

Value(s)

Yes

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

Go to Step 2

Go to A Powertrain On Board Diagnostic (OBD) System Check

Turn the ignition OFF.
Turn the air conditioning system OFF.

Caution: Relieve the fuel system pressure before servicing fuel system components in order to reduce the risk of fire and personal injury.

After relieving the system pressure, a small amount of fuel may be released when servicing the fuel lines or connections. In order to reduce the chance of personal injury, cover the regulator and the fuel line fittings with a shop towel before disconnecting. This will catch any fuel that may leak out. Place the towel in an approved container when the disconnection is complete.

Install the J 34730-1A fuel pressure gauge. Refer to the illustration associated with the circuit description.
Place the bleed hose of the fuel pressure gauge into an approved gasoline container.
Turn the ignition ON.
Bleed the air out of the fuel pressure gauge.
Turn the ignition OFF for 10 seconds.
Turn the ignition ON.

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

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

Is the fuel pressure within the specified limits?

333-376 kPa (48-55 psi)

Go to Step 3

Go to Step 12

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

Note fuel pressure after pump stops running.
Does the fuel pressure drop more than the specified value in 10 minutes?

34 kPa (5 psi)

Go to Step 10

Go to Step 4

Relieve fuel pressure to the specified value.
Monitor the fuel pressure.

Does pressure drop more than the specified value in 10 minutes?

69 kPa (10 psi)

14 kPa (2 psi)

Go to Step 18

Go to Step 5

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

Go to Step 6

Go to Step 8

Visually and physically inspect the following items for a restriction:

•	The in-pipe fuel filter.

•	The fuel feed pipe.

Was a restriction found?

Go to Step 23

Go to Step 7

Remove the fuel 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.

•	The fuel pump strainer for correct position and installation on fuel sender assembly.

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

Was a problem found in any of these areas?

Go to Step 23

Go to Step 18

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

If engine fails to start, go to Engine Cranks but Does Not Run .

Does the fuel pressure drop by the amount specified?

21-69 kPa (3-10 psi)

Go to Symptoms

Go to Step 9

Important: The fuel pressure regulator vacuum line should be inspected for fuel leaks from the regulator diaphragm.

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 drop by the amount specified?

21-69 kPa (3-10 psi)

Go to Step 19

Go to Step 20

Turn the Ignition OFF. Relieve the fuel pressure. Refer to the Fuel Pressure Relief Procedure .
Disconnect the fuel feed pipe and the fuel return pipe from the fuel rail. Refer to Servicing Quick Connect Fittings .
Install the J 37287 fuel pipe shut-off adapters between the fuel feed pipe and the fuel return pipe and the fuel rail. Refer to the illustration associated with the circuit description.
Open the valves on the Fuel Pipe Shut-Off Adapters.
Turn the Ignition ON.
Pressurize the fuel system by using a scan tool.
Place the bleed hose of the fuel pressure gauge into an approved gasoline container.
Bleed the air out of the fuel pressure gauge.
Wait for the fuel pressure to build.
Close the valve in the fuel pipe shut-off adapter that is connected to the fuel feed pipe.

Does the fuel pressure remain constant?

Go to Step 18

Go to Step 11

Open the valve in the fuel pipe shut-off adapter that is connected to the fuel feed pipe.
Pressurize the fuel system by using a scan tool.
Wait for the fuel pressure to build.
Close the valve in the fuel pipe shut-off adapter that is connected to the fuel return pipe.

Does the fuel pressure guage remain constant?

Go to Step 20

Go to Step 22

Is the fuel pressure above the specified limit?

376 kPa (55 psi)

Go to Step 13

Go to Step 15

Relieve the fuel pressure. Refer to the Fuel Pressure Relief Procedure .
Disconnect the fuel return pipe from the fuel Rail. Refer to Servicing Quick Connect Fittings .
Attach a length of flexible fuel hose to the fuel rail return outlet passage.
Place the open end of the flexible fuel hose into an approved gasoline container.
Turn the Ignition OFF for approximately 10 seconds.
Turn the Ignition ON.
Observe the fuel pressure with the Fuel Pump running.

Is the fuel pressure within the specified limits?

333-376 kPa (48-55 psi)

Go to Step 23

Go to Step 14

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

Was a restriction found?

Go to Step 24

Go to Step 21

Is the fuel pressure above the specified value?

0 kPa (0 psi)

Go to Step 16

Go to Step 17

Relieve the fuel pressure. Refer to Fuel Pressure Relief Procedure .
Disconnect the fuel return pipe from the fuel rail. Refer to the Servicing Quick Connect Fittings .
Install the J 37287 fuel pipe shut-off adapter between the fuel return pipe and the fuel rail. Refer to the illustration associated with the circuit description.
Open the valve on the fuel pipe shut-off adapter.
Turn the ignition OFF.
Pressurize the fuel system by using a scan tool.
Place the bleed hose of the fuel pressure gauge into an approved gasoline container.
Bleed the air out of the fuel pressure gauge.

Notice:: Do not allow the fuel pressure to exceed 414 kPa (60 psi). Fuel Pressure in excess of 414 kPa (60 psi) may damage the fuel pressure regulator.

Slowly close the valve in the Fuel Pipe Shut-Off Adapter that is connected to the Fuel Return Pipe.

Does the fuel pressure rise above the specified value?

333-376 kPa (48-55 psi)

Go to Step 21

Go to Step 7

Perform fuel system electrical check. Refer to DTC P0231 Fuel Pump Feedback Circuit Low Voltage diagnosis.

Was a problem found with the fuel pump electrical circuit?

Go to Step 24

Go to Step 18

Visually and physically inspect the following items:

•	The in-line fuel filter for obstructions.

•	The fuel feed pipe for a restriction.

•	The fuel pump strainer for obstructions.

•	The fuel pump flex pipe for leaks.

Important: It will be necessary to remove the fuel sender assembly in order to inspect the fuel pump strainer and the fuel pump flex pipe. Refer to Fuel Sender Assembly Replacement .

Was a problem found in any of these areas?

Go to Step 24

Go to Step 19

Replace the modular fuel sender assembly. Refer to Fuel Sender Assembly Replacement .

Is the action complete?

Go to Step 25

Locate and repair the loss of vacuum to the fuel pressure regulator.

Is the action complete?

Go to Step 25

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

Is the action complete?

Go to Step 25

Lift fuel rail and injectors. Refer to Fuel Injection Fuel Rail Assembly Replacement .
Locate and replace any leaking fuel injector(s).
If a fuel injector leak is not found, locate the fuel rail assembly leak.
Replace the fuel rail assembly.

Is the action complete?

Go to Step 25

Locate and correct the restriction in the fuel return pipe.

Is the action complete?

Go to Step 25

Repair the problem as necessary.

Is action complete?

Go to Step 25

Turn the ignition OFF.
Turn the air conditioning system OFF.

Caution: Relieve the fuel system pressure before servicing fuel system components in order to reduce the risk of fire and personal injury.

Install the J 34730-1A fuel pressure gauge. Refer to the illustration associated with the circuit description.
Place the bleed hose of the fuel pressure gauge into an approved gasoline container.
Turn the ignition ON.
Bleed the air out of the fuel pressure gauge.
Turn the ignition OFF for 10 seconds.
Turn the ignition ON.

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

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

Is the fuel pressure within the specified limits?

333-376 kPa (48-55 psi)

Go to Step 26

Go to Step 12

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

Note fuel pressure after pump stops running.
Does the fuel pressure drop more than the specified value in 10 minutes?

34 kPa (5 psi)

Go to Step 4

System OK