Truck is a 05.5 with the lift pump in the tank. It has a rough idle and the code P0628 popped up. Is the lift pump going out? When you turn the key on you can only hear it for 2 or 3 seconds. The only thing is the rough idle other than that no hard starting , stumbling , or cutting out. Also no gauges to measure fuel pressure. Would a bad FCA throw this code?? Any help appreciated..

 

That is the code for the lift pump, but it doesn't make sense that it would idle rough and still have good power higher up the rev range. Mine runs for about 25 seconds when I turn on the key without starting.

 

Here is test procedure, could be pump or relay bad.
P0628-LOW VOLTAGE DETECTED AT THE FUEL LIFT PUMP
For a complete wiring diagram Refer to Section 8W.
When Monitored:
While the key is on.
Set Condition:
The commanded signal to the fuel lift pump relay does not match the feedback signal from the fuel lift pump relay.

Possible Causes
WIRING HARNESS
FUEL LIFT PUMP RELAY
FUEL LIFT PUMP RELAY DRIVER CIRCUIT SHORTED TO EXTERNAL VOLTAGE
FUEL LIFT PUMP RELAY DRIVER CIRCUIT OPEN
FUEL LIFT PUMP RELAY GROUND CIRCUIT OPEN
FUEL LIFT PUMP RELAY GROUND CIRCUIT SHORTED TO EXTERNAL VOLTAGE
ECM


Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING)

Diagnostic Test
1. LIFT PUMP RUNS

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Remove the cover to the PDC.
Turn the ignition on, engine off.
With the scan tool, in system test actuate the lift pump relay.

Does the fuel lift pump relay click when the lift pump is actuated?

Yes
Test complete.
Perform Intermittent Condition test. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING)

No
Go To 2



2. LIFT PUMP RELAY DOES NOT CLICK

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Turn Ignition off.
Remove the lift pump relay from the PDC.
Turn the ignition on.
Connect one end of an incandescent test light to battery negative.
Connect the other end of the test light to the relay driver pin in the PDC.
With the scan tool, in system test actuate the lift pump relay.

Does the test light illuminate brightly?

Yes
Go To 3

No
Go To 5



3. FUEL LIFT PUMP GROUND CIRCUIT OPEN

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Connect one end of an incandescent test light to battery postive.
Connect the other end of the test light to the relay ground pin in the PDC.

Is the resistance less than 1 Ohms?

Yes
Go To 4

No
Repair the open ground circuit.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)



4. LIFT PUMP RELAY

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Install a know good relay in place of the fuel lift pump relay.
With the scan tool, in system test actuate the lift pump relay.

Does the fuel lift pump relay click when the lift pump is actuated?

No
Go To 5

Yes
Replace the lift pump relay.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)



5. FUEL LIFT PUMP DRIVER CIRCUIT OPEN

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Turn Ignition off.
Disconnect the ECM connectors.

NOTE: Check connectors - Clean/repair as necessary.


Using an ohmmeter, measure the resistance of the lift pump relay driver wire between the ECM connector and the PDC.

Is the resistance less than 10 Ohms?

No
Repair the Fuel lift pump driver circuit open.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)

Yes
Go To 6



6. FUEL LIFT PUMP RELAY DRIVER CIRCUIT SHORTED TO EXTERNAL VOLTAGE

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Measure the voltage between battery negative and the relay driver circuit in the PDC.

Is the voltage greater than 1 volt?

Yes
Repair the Fuel lift pump Relay driver circuit shorted to voltage.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)

No
Go To 7



7. FUEL LIFT PUMP RELAY DRIVER CIRCUIT SHORTED TO OTHER CIRCUITS

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Measure the resistance between the lift pump relay driver circuit in the ECM connector and all other circuits in the ECM connectors.

Is the resistance less than 10 Ohms?

Yes
Repair the Fuel lift pump Relay driver circuit shorted to another circuit.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)

No
Go To 8



8. ECM

--------------------------------------------------------------------------------
Reconnect the ECM connectors.
Turn the ignition on, engine off.
Connect one end of an incandescent test light to battery negative.
Connect the other end of the test light to the relay driver pin in the PDC.
Using the scan tool, actuate the lift pump.

Does the test light illuminate brightly?

Yes
Repair complete.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)

No
Replace the ECM.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)

 

Under warranty?

 

BigIron70, terrific comeback, now if I could perform them steps I'd be in great shape. Lets see if I can do it and still go to work.Thank you. Annabelle , no the truck is not under warranty,170,000 plus on the OD truck runs fine except for the rough idle.With that amount of mileage I"d say pump should be changed (got to be in Duncan Ok. monday morning, let me make one more run out of her)

 

No fuel pressure guage? Does the Quad read fuel pressure?

I would add a better lift pump just to be sure CP3 is getting what it wants and add a better low micron aftermarket filter also with the miles you have.