In Tank Lift Pump vs High Pressure Fuel Pump

DocB · **Posted:** Mon Nov 13, 2017 2:13 pm

Thanks fellas. Thinking about getting the whole shebang from Sasquatch. Just awaiting their response if a wiring harness is available.
Still wondering what the intermittant humming sound is coming from the fuel tank area at start up. Sort of like an on/off stuck motor sound.

@Jeff-might not be a bad idea to install the heater stand pipe while the tank is down.

APC9199 · **Posted:** Mon Nov 13, 2017 2:59 pm

DocB wrote:

Thanks fellas. Thinking about getting the whole shebang from Sasquatch. Just awaiting their response if a wiring harness is available.
Still wondering what the intermittant humming sound is coming from the fuel tank area at start up. Sort of like an on/off stuck motor sound.

@Jeff-might not be a bad idea to install the heater stand pipe while the tank is down.

There shouldn't be anything in the rear of the vehicle that will make that noise unless there is some aftermarket electronic device back there (AMP, speakers, etc). What you are hearing is most likely a lift pump! An easy way to check would be to open the hood and locate the relay supplying power to the lift pump wiring. Turn the key on (do not start) and quickly pull the relay. You only have about 15 seconds to do this before the pump shuts off automatically, so be quick! If the sound stops when you pull the relay, then you likely have a lift pump already. Alternatively, you could open the bleeder valve on the fuel filter head with a piece of tube connected to it. Feed it into a bottle, then turn the ignition on (do not start). If fuel starts flowing steadily, you have a lift pump.

WWDiesel · **Posted:** Mon Nov 13, 2017 4:03 pm

APC9199 wrote:

DocB wrote:

Thanks fellas. Thinking about getting the whole shebang from Sasquatch. Just awaiting their response if a wiring harness is available.
Still wondering what the intermittant humming sound is coming from the fuel tank area at start up. Sort of like an on/off stuck motor sound.

@Jeff-might not be a bad idea to install the heater stand pipe while the tank is down.

There shouldn't be anything in the rear of the vehicle that will make that noise unless there is some aftermarket electronic device back there (AMP, speakers, etc). What you are hearing is most likely a lift pump! An easy way to check would be to open the hood and locate the relay supplying power to the lift pump wiring. Turn the key on (do not start) and quickly pull the relay. You only have about 15 seconds to do this before the pump shuts off automatically, so be quick! If the sound stops when you pull the relay, then you likely have a lift pump already. Alternatively, you could open the bleeder valve on the fuel filter head with a piece of tube connected to it. Feed it into a bottle, then turn the ignition on (do not start). If fuel starts flowing steadily, you have a lift pump.

X2, excellent advice! :wink:

DocB · **Posted:** Sun Dec 03, 2017 3:14 pm

Usually, normal fuel rail pressure is about 5K PSI at idle (perhaps a tad under) read by gauge.
When it fluctuates, it'll jump quickly down to 2.5K then to 7.5K then back to 5K.

flash7210 · **Posted:** Sun Dec 03, 2017 3:29 pm

DocB wrote:

Usually, normal fuel rail pressure is about 5K PSI at idle (perhaps a tad under) read by gauge.
When it fluctuates, it'll jump quickly down to 2.5K then to 7.5K then back to 5K.

Have you scanned for codes?

What you describe could be a loose connection at the fuel rail pressure sensor or at the fuel quantity solenoid.

Been there done that with both.

GordnadoCRD · **Posted:** Sun Dec 03, 2017 4:36 pm

Quote:

7. CHECKING FOR AIR IN FUEL SYSTEM
With the scan tool in Sensors, compare the Fuel Pressure Setpoint with the Actual Fuel Pressure readings.
NOTE: If there is air in the fuel system, the Actual Fuel Pressure will oscillate more than 100 psi above
and/or below the Fuel Pressure Setpoint.
Does Actual Fuel Pressure oscillate more than 100 psi above and/or below the Fuel Pressure Setpoint?
Yes >> Refer to the Service Information to purge air from the fuel system.
Perform the ECM Verification Test Ver. 1. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING)
No >> Go To 8

8. FUEL PRESSURE SOLENOID
With the scan tool, compare the Fuel Pressure Setpoint with the actual Fuel Pressure.
NOTE: A sticking Fuel Pressure Solenoid is indicated by the actual Fuel Pressure gradually dropping below
the Fuel Pressure Setpoint then suddenly increasing (spiking) above the Fuel Pressure Setpoint.
Does the actual Fuel Pressure gradually decrease then suddenly increase (spike) above the Fuel Pressure
Setpoint?

In Tank Lift Pump vs High Pressure Fuel Pump

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