Fuel System Pressure Test. Chevrolet S10 Pickup

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1996 🢒 S10 Pickup - 2WD 🢒 Engine 🢒 Engine Controls - 4.3L (VIN W) 🢒 Fuel System Pressure Test


(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 remains on as long as the engine cranks or runs and the PCM receives reference pulses. If no reference pulses exist, 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 in order 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 returns to the fuel tank by a separate fuel return pipe.

Test Description

The numbers below refer to the step numbers in the diagnostic table.

In order to relieve the fuel pressure, refer to Fuel Pressure Relief . With the ignition switch ON and the fuel pump running, the fuel pressure indicated by the fuel pressure gauge should be 284-325 kPa (41-47 psi).

A fuel system that cannot maintain a constant fuel pressure may have a leak in one or more of the following areas:

•	The Fuel Pump Check Valve

•	The Fuel Pump Connecting Hose

•	The Valve or Valve Seat within the Fuel Pressure Regulator

•	The Fuel Injectors

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

A fuel pressure which drops off during acceleration, cruise, or a hard cornering may cause a lean condition. A lean condition can cause a loss of power, surging, or a misfire. A scan tool can diagnose a lean condition. If an extremely lean condition occurs, the Oxygen Sensors will stop toggling. The oxygen sensor output voltages will drop below 500 mV. Also the Fuel Injector Pulse Width will increase.

When the engine idles, the manifold pressure is low (high vacuum). This low pressure (high vacuum) is applied to the fuel pressure regulator diaphragm by the spring inside the fuel pressure regulator. When this happens, the result is lower fuel pressure. The fuel pressure at idle 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. The driveability condition associated with rich condition can include a hard starting (followed by black smoke) and a strong sulfur smell from 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. The 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 causes the fuel pressure to rise above the regulated fuel pressure. Using a scan tool in order to pressurize the system, the fuel pressure should rise above 325 kPa (47 psi) as the gauge 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.

Step

Action

Value(s)

Yes

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

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Turn OFF the ignition.
Turn OFF the air conditioning system.
Relieve the fuel pressure. Refer to the Fuel Pressure Relief .
Install the fuel pressure gauge. Refer to figure on the facing page.
Turn ON the ignition.
Bleed the air out of the fuel pressure gauge into an approved gasoline container.
For 10 seconds, turn OFF the ignition.
Turn ON the ignition.

Important: The fuel pump will run for approximately 2 seconds. Cycle the ignition 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?

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. After 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 fuel pump. Refer to Fuel Sender Assembly Replacement (Fuel Pump) .
Visually and physically inspect the following items:

•	The fuel pump strainer for a restriction

•	The fuel pump coupling hose for leaks.

Was a problem found in any of these areas?

Go to Step 25

Go to Step 21

Turn ON the ignition and the engine.
Allow the engine to idle at the normal operating temperature.

Does the fuel pressure drop by the amount specified?

21-69 kPa (3-10 psi)

Go to Driveability 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 gauge drop by the amount specified?

21-69 kPa (3-10 psi)

Go to Step 19

Go to Step 20

Turn OFF the ignition.
Place the bleed hose of the fuel pressure gauge into an approved gasoline container.
Turn ON the ignition.
Bleed the air out of the fuel pressure gauge.
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 gauge inlet hose (refer to A on the illustration.

Does the fuel pressure remain constant?

Go to Step 21

Go to Step 10

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

Does the fuel pressure indicated by the fuel pressure gauge 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 gauge into an approved gasoline container and opening the relief valve.
Disconnect the fuel return hose fitting. Refer to the figure.
Place the open end of the flexible hose into an approved gasoline container.
For approximately 10 seconds, turn OFF the ignition.
Turn ON the ignition.
Observe the fuel pressure indicated by the fuel pressure gauge 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 return 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 physically inspect the fuel pressure regulator filter screen and 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 gauge into an approved gasoline container and opening the relieve valve.
Using a scan tool, pressurize the fuel system.
Bleed the air out of the fuel pressure gauge.

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