K Tahoe 4WD V8-4.8L VIN V (2000)
^ The fuel injectors
4. A fuel system that drops more than 14 kPa (2 psi) in 10 minute after being relieved to 69 kPa (10 psi) indicates a leaking fuel pump check valve.
5. 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. You can diagnose a lean condition using a scan tool. It an extremely lean condition occurs, the heated oxygen sensors will stop
toggling. The heated oxygen sensor output voltages will drop below 300 mV. The fuel injector pulse 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.
8. When the engine is at idle, the manifold pressure is low. This low pressure is applied to the fuel pressure regulator diaphragm. The low pressure
will offset the pressure being 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 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.
12. A rich condition may result from the fuel pressure being above 427 kPa (62 psi). A rich condition may cause DTC P0132, DTC P0152, DTC
P0172 or DTC P0175 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 the fuel pressure being below 379 kPa (55 psi). A lean condition may cause DTC P0131, DTC P0151, DTC
P0171, or DTC P0174 to set. Driveability conditions associated with lean conditions can include hard starting, 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. Using a scan
tool to pressurize the fuel system, the fuel pressure should rise above 427 kPa (62 psi) as the valve on the fuel pipe shut-off adapter connected to
the fuel return pipe becomes partially closed.
22. 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:
A. Remove the fuel rail.
B. Reinstall the crossover pipe to the right fuel rail.
C. Connect the fuel feed pipe and the fuel return pipe to the fuel rail.
D. Lift the fuel rail just enough to leave the fuel injector nozzles in the fuel injector ports.
E. Pressurize the fuel system by using the scan tool fuel pump enable.
F. Visually and physically inspect the fuel injector nozzles for leaks.
