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Fuel System Pressure Test (VIN 1)
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Low Mount 3800 ALT!
Low mounts in stock today. Newest design has
tension belt assembly, cleaned, and blasted.
Checking and testing your Fuel Pressure on a
L67
What is the fuel pressure of a L67 engine. GM
service manual indicates 45-55 PSI at the rail test point. I have run as high as
62PSI, but the average on modified engines with the stock injectors is 58PSI.
Should you run these pressures? It is up to you and your tuning ability, and
what PCM programming you have. What works 100% for one person, does not work
100% for another person. Its an average of information, and what the engine is
happy with.
Service manual outline on troubleshooting Fuel
Pressures :
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|
|
(1) |
Fuel Pipe Shut-off Adapters |
|
(2) |
Fuel Return Pipe |
|
(3) |
Fuel Pump Flex Pipe |
|
(4) |
Modular Fuel Sender |
|
(5) |
Fuel Feed Pipe |
|
(6) |
In-Line Fuel Filter |
|
(7) |
Fuel Rail Assembly |
|
(8) |
Fuel Pressure Regulator |
|
(9) |
Fuel Pressure Guage |
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 the fuel feed pipe, and
in-line fuel filter to the Fuel Rail Assembly. The fuel pump is designed to
provide fuel at a pressure that is above the pressure needed by the fuel
injectors. A fuel pressure regulator, attached to the Fuel Rail, 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. The fuel pressure gauge J
34730-1A and fuel pipe shut off adapters J 37287 are used for fuel system
diagnosis.
Test Description
The numbers below refer to the step numbers on the Diagnostic Table.
2.
This step tests the system's ability to achieve the specified fuel
pressure.
3.
A fuel system that drops more than 5 psi during 10 minutes 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 |
-
5.
Fuel pressure that drops-off during acceleration, during cruise, or
during hard cornering may cause a lean condition. A lean condition can cause a
loss of power, surging, or misfire. You can diagnose a lean condition with scan
tool. If an extremely lean condition occurs, the oxygen sensors will stop
toggling. The oxygen sensor output voltages will drop to less than 500 mV. Also,
the fuel injector width will increase.
Important: Ensure
that the fuel system is not operating in the Fuel Cut-Off Mode. This can cause
false indications from the scan tool.
8.
When the engine is at idle, the manifold pressure is low, indicating a
high vacuum. This low pressure is applied to the fuel pressure regulator
diaphragm. The low pressure will offset the pressure that is being applied to
the fuel pressure regulator diaphragm by the spring inside the fuel pressure
regulator. When this occurs, the result is lower fuel pressure. The fuel
pressure at idle will vary slightly during 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.
12.
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.
13.
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.
15.
A lean condition may result from fuel pressure that is less than 333 kPa
(48 psi). A lean condition may cause a DTC P0131 or a DTC P0171 to set.
Driveability conditions that are associated with lean conditions can include
hard starting when the engine is cold, hesitation, poor driveability, lack of
power, surging, and misfiring.
16.
Restricting the fuel return pipe with the fuel pipe shut-off adapter
causes the fuel pressure to rise above the regulated fuel pressure. Use a scan
tool in order to pressurize the system. The fuel pressure should rise to more
than 376 kPa (55 psi) when the valve on the fuel pipe shut-off adapter that is
connected to the fuel return pipe becomes partially closed.
Notice: Do
not allow the fuel pressure to exceed 450 kPa (65 psi). Fuel pressure in excess
of 450 kPa (65 psi) may damage the Fuel Pressure Regulator.
22.
Check the spark plug that is associated with a particular fuel injector
for fouling or for saturation in order to determine if that particular fuel
injector is leaking.
|
Step |
Action |
Value(s) |
Yes |
No |
|
1 |
Did you perform the Powertrain
On-Board Diagnostic (OBD) System Check? |
-- |
Go to Step 2 |
Go to Powertrain On Board
Diagnostic (OBD) System Check |
|
2 |
- Turn OFF the ignition.
- Turn OFF the air conditioning system.
Caution: Wrap a
shop towel around the fuel pressure connection in order to reduce the
risk of fire and personal injury. The towel will absorb any fuel leakage
that occurs during the connection of the fuel pressure gage. Place the
towel in an approved container when the connection of the fuel pressure
gage is complete.
- Install the J 34730-1A fuel pressure gauge.
- 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
into an approved gasoline container.
- Turn OFF the ignition for 10 seconds.
- 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 level
- With the fuel pump running, observe the fuel
pressure that is indicated by the fuel pressure gauge.
Is the fuel pressure within the specified limits? |
333-376 kPa (48-55 psi) |
Go to Step 3 |
Go to Step 12 |
|
3 |
Important: The fuel pressure may
vary slightly when the fuel pump stops running. The fuel pressure should
stabilize and remain constant. Note the fuel pressure after the
fuel 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 |
|
4 |
Relieve the fuel pressure to the
specified value. Does the fuel pressure drop more than the specified
value in 10 minutes? |
69 kPa (10 psi)
14 kPa (2 psi) |
Go to Step 19 |
Go to Step 5 |
|
5 |
Is the fuel pressure suspected
of dropping-off during acceleration, during cruise, or during hard
cornering? |
-- |
Go to Step 6 |
Go to Step 8 |
|
6 |
Inspect the following items for
a restriction:
|
• |
The in-line fuel filter |
Did you find a restriction? |
-- |
Go to Step 24 |
Go to Step 7 |
|
7 |
- Remove the modular sender assembly. Refer to
Fuel Sender Assembly Replacement .
- Inspect the following components:
|
- |
The fuel pump strainer for a restriction
|
-
|
- |
The fuel pump strainer for correct
position, and for correct installation on the fuel sender
assembly |
-
|
- |
The fuel pump flex pipe for leaks |
-
|
- |
Verify that the fuel pump is the correct
fuel pump for this vehicle |
Did you find a problem in any of these areas? |
-- |
Go to Step 24 |
Go to Step 19 |
|
8 |
- Turn OFF the ignition 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. Note this
pressure.
- Start the engine.
- Allow the engine to idle at the normal
operating temperature.
Is the fuel pressure less than the noted fuel pressure by the amount
specified? |
21-69 kPa (3-10 psi) |
Go to Symptoms |
Go to Step 9 |
|
9 |
- 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 20 |
Go to Step 21 |
|
10 |
- Relieve the fuel pressure. Refer to Fuel
Pressure Relief Procedure
- Disconnect the fuel feed pipe and the fuel
return pipe from the fuel rail. Refer to Quick Connect Fitting(s)
Service (Metal Collar)
- Install the J 37287 fuel pipe shut-off
adapters between the fuel feed pipe and the fuel return pipe and the
fuel rail.
Notice: Do
not allow the fuel pressure to exceed 450 kPa (65 psi). Fuel pressure in
excess of 450 kPa (65 psi) may damage the Fuel Pressure Regulator.
- Open the valves on the fuel pipe shut-off
adapters.
- Turn OFF the ignition.
- Use a scan tool in order to pressurize the
fuel system.
- 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 19 |
Go to Step 11 |
|
11 |
- Open the valve in the fuel pipe shut-off
adapter that is connected to the fuel feed pipe.
- Use a scan tool in order to pressurize the
fuel system.
- 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 remain constant? |
-- |
Go to Step 21 |
Go to Step 22 |
|
12 |
Is the fuel pressure above the
specified limit? |
376 kPa (55 psi) |
Go to Step 13 |
Go to Step 15 |
|
13 |
- Relieve the fuel pressure. Refer to Fuel
Pressure Relief Procedure
- Disconnect the fuel return pipe from the fuel
rail. Refer to Quick Connect Fitting(s) Service (Metal Collar)
- Attach a length of flexible fuel hose to the
fuel rail return outlet passage
- Place the open end of the flexible hose into
an approved gasoline container.
- Turn OFF the ignition for 10 seconds.
- Turn ON the ignition.
- With the fuel pump running, observe the fuel
pressure gauge.
Is the fuel pressure within the specified limits? |
333-376 kPa (48-55 psi) |
Go to Step 23 |
Go to Step 14 |
|
14 |
Inspect the fuel rail outlet
passages for a restriction. Did you find a restriction? |
-- |
Go to Step 24 |
Go to Step 21 |
|
15 |
Is the fuel pressure more than
the specified value? |
0 kPa (0 psi) |
Go to Step 16 |
Go to Step 17 |
|
16 |
- Relieve the fuel pressure. Refer to Fuel
Pressure Relief Procedure
- Disconnect the fuel return pipe from the fuel
rail. Refer to Quick Connect Fitting(s) Service (Metal Collar)
- Install the J 37287 fuel pipe shut-off adapter
between the fuel return pipe and the fuel rail.
- Open the valve on the fuel pipe shut-off
adapter.
- Turn OFF the ignition.
- Use a scan tool in order to pressurize the
fuel system.
Notice: Do
not allow the fuel pressure to exceed 450 kPa (65 psi). Fuel pressure in
excess of 450 kPa (65 psi) may damage the Fuel Pressure Regulator.
- Place the bleed hose of the fuel pressure
gauge into an approved gasoline container.
- Bleed the air from the fuel pressure gauge.
- 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 |
|
17 |
Perform the Fuel System
Electrical Test. Refer to Fuel Pump Electrical Circuit Diagnosis . Did
you find a problem with the fuel pump electrical circuit? |
-- |
Go to Step 24 |
Go to Step 18 |
|
18 |
Inspect the following
components:
|
• |
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: You
must 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
Did you find a problem in any of these areas? |
-- |
Go to Step 24 |
Go to Step 19 |
|
19 |
Replace the modular fuel sender
assembly. Is the action complete? |
-- |
Go to Step 25 |
-- |
|
20 |
Locate and repair the loss of
vacuum to the fuel pressure regulator. Is the action complete? |
-- |
Go to Step 25 |
-- |
|
21 |
Replace the fuel pressure
regulator. Is the action complete? |
-- |
Go to Step 25 |
-- |
|
22 |
Locate and replace any leaking
fuel injectors. Is the action complete? |
-- |
Go to Step 25 |
-- |
|
23 |
Locate and correct the
restriction in the fuel return pipe. Is the action complete? |
-- |
Go to Step 25 |
-- |
|
24 |
Repair the problem as necessary.
Is the action complete? |
-- |
Go to Step 25 |
-- |
|
25 |
- Turn OFF the ignition.
- Turn OFF the air-conditioning system.
Caution: Wrap a
shop towel around the fuel pressure connection in order to reduce the
risk of fire and personal injury. The towel will absorb any fuel leakage
that occurs during the connection of the fuel pressure gage. Place the
towel in an approved container when the connection of the fuel pressure
gage is complete.
- Install the J 34730-1A fuel pressure gauge.
- Place the bleed hose of the fuel pressure
gauge into an approved gasoline container.
- Turn ON the ignition.
- Bleed the air from the fuel pressure gauge
into an approved gasoline container.
- Turn OFF the ignition for 10 seconds.
- 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 level
- With the fuel pump running, observe the fuel
pressure that is indicated by the fuel pressure gauge. Is the fuel
pressure within the specified limits?
|
333-376 kPa (48-55 psi) |
Go to Step 26 |
Go to Step 11 |
|
26 |
Important: The fuel pressure may
vary slightly when the fuel pump stops running. The fuel pressure should
stabilize and remain constant. Note the fuel pressure after the
fuel pump stops running.
Does the fuel pressure drop more than the specified value during
10 minutes? |
34 kPa (5 psi) |
Go to Step 10 |
System OK |
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