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Duramax Fifth Generation: 2011-2016 (LML) Discuss the fifth generation (2011-2016) of the 6.6L Duramax diesel engine & associated components. Engine related discussion ONLY.

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Old 10-31-2019, 08:59 AM   #1 (permalink)
C10Racer
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Hard start, no codes, good fuel pressure

I've got an '11 truck that is a bear to start; we have to pump the manual primer by hand until its hard then pump it while cranking to get it to start. The truck usually runs fine once it is running but occasionally when accelerating it'll fall on its face like a gas motor that has gone lean. We have monitored the fuel pressure (through OBD) and it seems to track well with no issues; we also replaced the fuel filter assembly. My only guess is that the CP4 is failing to build enough suction to draw fuel in and is on the way out? Will a lift pump install help longterm/short-term to keep it running?

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Old 10-31-2019, 12:41 PM   #2 (permalink)
redwngr
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Cracked/damaged fuel filter head.
Cracked/damaged/loose WIF sensor.
Filter o-ring issue - not fully sealed.

When the 'filter assy' was replaced, did that include the filter head?

Are you positive the fuel filter o-ring's are correctly seated?

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Old 10-31-2019, 08:44 PM   #3 (permalink)
Ron Nielson
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Can you monitor the fuel pressure/vacuum while cranking? If you had a CP3 pump, the specs say it should pull a vacuum of 5 in hg while cranking. Not ur if the CP4 spec is the same or not. Following is aditional information for my 2008 model:

An Engine Cranks but Will Not Run or Hard Start symptom may exist if air is being drawn into the fuel injection system due to the following conditions:

Fuel contamination-Refer to Contaminants-in-Fuel Diagnosis. See: Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics\Contaminants-in-Fuel Diagnosis
Deformed or cut O-rings at the fuel supply line connections
Improperly seated fuel supply line fittings
Porous or weathered rubber fuel supply lines
Fuel filter vent screw not tighten or cross threaded
Fuel filter not tighten properly

Special Tools

J 23738-A MityVac
EN-47969 Fuel Supply Diagnostic Hose
CH-48027 Digital Pressure Gage
J 44581 Fuel Line Disconnect Tool

Circuit/System Verification

Observe the Actual Fuel Rail Pressure parameter with a scan tool. During engine cranking, the pressure should be at least 10 MPa. With the engine running at idle the pressure should be close to the Desired Fuel Rail Pressure. As the engine speed increase, the Desired Fuel Rail Pressure and the Actual Fuel Rail Pressure should be within 2 MPa of each other.

Circuit/System Testing

Important: Ensure that a sufficient amount of fuel is in the fuel tank to run the vehicle.

Install the CH-48027 to the fuel system service port on the right front side of the engine.
Prime the fuel system until 10 psi is indicated on the CH-48027. Fuel pressure should not drop below 2 psi in less than one minute.

If fuel pressure drops below 2 psi in less than one minute, go to step 4.

Important: It may be necessary to remove engine components for the visual inspections.

Attempt to start and idle the engine. Observe the CH-48027 during idle. The vacuum should be between 1-3 in Hg.

If more than 3 in Hg is observed at idle, visually inspect the following items:
Fuel filter element for a restriction
Hoses and lines that are flattening when the engine is running, or have kinks that would restrict the flow of fuel
If engine did not start or no vacuum was observed, refer to Fuel Injection Pump Replacement.

Disconnect the fuel supply line at the engine and install a J 23738-A using the J 44581.
Apply vacuum to the fuel supply pipe until 25 in Hg has been reached. Wait for at least one minute to allow the fuel system to stabilize. Vacuum should not drop below 8 in Hg within 10 minutes.

If vacuum cannot be obtained or the vacuum drops below 8 in Hg within 10 minutes, repair the air leak at fuel filter/heater element housing connections or at the fuel hoses/pipes on the engine supply line.

Remove both hoses from the fuel filter/heater element housing assembly. Cap the suction side port of the fuel filter/heater element housing assembly. Apply 25 in Hg to the discharge port of the fuel filter/heater element housing assembly. Vacuum should not drop below 8 in Hg within 10 minutes.

If vacuum drops below 8 in Hg within 10 minutes, replace the fuel filter/heater element housing assembly.

Important: The engine may start and then stall after briefly running.

Remove the J 23738-A from the fuel filter/heater element housing assembly. Install the removed fuel filter/heater element housing assembly, and cap off the fuel supply pipe on the engine. Crank the engine in 15-second intervals while observing the CH-48027. More than 5 in Hg vacuum should be observed during cranking.

If less than 5 in Hg was observed on the vacuum gage during cranking, replace the fuel injection pump.

Important: The engine may start, and then stall after briefly running.

Install the fuel supply line at the engine, and disconnect the chassis fuel supply line at the fuel tank. Install a J 23738-A to the supply hose at the fuel tank using the J 44581.
Apply vacuum to the supply hose at the fuel tank until 25 in Hg has been reached. Wait for a least one minute for the fuel system to stabilize. Vacuum should not drop below 8 in Hg within 10 minutes.

If vacuum cannot be obtained, or the vacuum drops below 8 in Hg within 10 minutes, repair the air leak in the fuel supply line between the engine and fuel tank, or the connection of the supply line to the engine.

Install all components and lines that were previously removed or disconnected.
Install the EN-47969 on the fuel supply line at the engine. Create a vertical loop in the hose to observe the incoming fuel for air bubbles.
Open the bleed screw on top of the fuel filter/heater element housing. Prime the system until fuel appears at the bleed screw. Continue to prime the fuel system until the engine starts and runs.
Run the engine for at least 10 minutes to allow the fuel system to stabilize, and purge any air from the system.

Important: Changes in engine speed can cause an increase of air bubbles that enter the EN-47969. An air pocket at the top of the EN-47969 loop is considered a normal condition.

At a stabilized idle, observe the fuel entering the EN-47969 for air bubbles.

If air bubbles were observed entering the transparent hose, test the fuel sender for leaks.

Install the fuel sender, fuel tank, and all fuel system connections and components that were previously disconnected. Leave the EN-47969 connected to the fuel supply line. Prime the fuel system 30 times to remove the air from the fuel hoses. Continue to prime the fuel system until the engine starts and runs. Observe the fuel entering the transparent hose.

If air bubbles are still present, refer to Diagnostic Aids.
If no air bubbles are present, remove the EN-47969 and run the engine to ensure no fuel leaks exist.
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