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I have a 05 C4500 crew cab 4x4 that has been parked for about 8 years.101K miles( Time flies!) I have been putting off this truck for way too long. Anyways over the years I bought new injectors (not rebuilt) and new CP3 when they came up for sale at a discount. The problem I am having is at best a hard start meaning if it starts its right before the computer cuts out the cranking time, and if it does start it is only when its cold.I have no engine codes. And if I remember right from 8 years ago, I think died a few times while driving as well.
Once it runs for a while it won't re start without enhancement. Since its been so long I don't remember all of the parameters regarding fuel rail pressure requirements for the engine to start. Mine will build about 1300 psi maybe 1400, compared to the desired being around 5000 psi. What is the psi requirement or psi number needed for reliable starting while cranking? Im assuming 1400 is too low. When running while parked the desired and actual rail psi are pretty close. I won't test drive this because I can't get stranded with this. 9K monster.
I have read about hard ,no start when hot and I am still confused about the steps I should take to diagnose. Ive read different forums and they seem to jump around with what to do first. And I should say I don't have any problems on my delivery pressure or system, I know that.
What should I try first? I do have a tech 2 its about 12 years old but it still seems to function which is a big plus, but its been so many years since Ive messed with DUramax/Tech 2s I forgot a lot. I could just start replacing parts as I have the 8 injectors and the CP3 but I would like to go about it the right way, and maybe it isn't even the main problem. Heres a picture after sitting in the shop for 8 years! I did mage to clean it up a bit, don't even ask me about the rat nest in the air cleaner! Thanks Nick
 

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Mine will build about 1300 psi maybe 1400, compared to the desired being around 5000 psi. What is the psi requirement or psi number needed for reliable starting while cranking?
It takes approximately 2500 PSI rail pressure to start.
 

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Welcome to DieselPlace

I moved your post over to "Med. Duty" for better views and responses to your issues and questions

:thumb:
 

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I'd put a new fuel filter assembly on it first. Wouldn't even think twice.

Priced around $100 on the web. P/n 12642624
 

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Here is something for you to think about or getting started to get your truck running. I would NOT start replacing parts, injectors, etc, until you have your truck running again , if at all possible.


Fuel System Diagnosis

Diagnostic Instructions



  • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
  • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
  • Diagnostic Procedure Instructions provides an overview of each diagnostic category.
Circuit/System Description

Fuel is drawn by the fuel injection pump from the tank to the engine through the fuel supply lines. Fuel flows to the fuel filter/heater element housing, which combines a water separator, a prime pump, fuel heater element and a filter element. A mechanical fuel injection pump at the front of the engine valley includes the fuel supply pump and the high-pressure pump. The small section of the fuel pump assembly is the supply pump, which creates a vacuum to pull fuel from the fuel tank to the high-pressure pump. The vacuum varies with engine load and speed as indicated by the table below. The pump is engine-driven by the camshaft gear. From the high-pressure pump, the pressurized fuel flows to the left fuel rail. A balance pipe from the center of the left rail then feeds the right fuel rail. Each fuel rail supplies one bank of 4 fuel injectors. The fuel rail pressure sensor is mounted in the end of the right fuel rail. Fuel is used to cool and lubricate the fuel injectors and fuel injection pump. The fuel return system is designed to return this fuel to the fuel tank. If the high side fuel pressure becomes excessive, the fuel rail pressure relief valve releases the fuel into the fuel return system. The return fuel travels through the fuel cooler and then to the fuel tank.







Diagnostic Aids

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.
  • 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.



  1. Install the CH-48027 to the fuel system service port on the right front side of the engine.
  2. 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.



  1. 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.
  1. Disconnect the fuel supply line at the engine and install a J 23738-A using the J 44581.
  2. 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.
  1. 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.



  1. 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.



  1. 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.
  2. 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.
  1. Install all components and lines that were previously removed or disconnected.
  2. 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.
  3. 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.
  4. 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.



  1. 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.
  1. 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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Discussion Starter #7
Thanks I didn't have a lot of time art all today but one thing I read that was easy to do was to command rail pressure and see how high I could get the pressure to go compared to the commanded PSI. I was told this would indicate a injector leak (not sure why it couldn't allo indicate other internal leaks, maybe that is just the most common problem, but anyways) I did this and the most it will develop at idle is around 13k, compared to over 22K commanded. After I did this I developed a knock, so when I deactivated each injector via Tech 2. It was very obviously number 7 that is knocking. What do you think of these symptoms? Thanks Nick
 

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Discussion Starter #8
Also I noticed that when cold it will develop about 1650 psi during cranking, this is enough to start the engine after a very prolonged cranking time, after warm it drops below 1300 psi and this appears not enough to start no matter how long the crank time. It will then restart after it cools down. Of course this isn't right but that are additional symptoms.
 

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Also I read the diagnosis info in one of the previous replies and although I appreciate the response I don't think any of the info provided is relevant to my problem. I did previously say I know I don't have a supply problem, I didn't want to go into detail as I thought that would be enough but I have a positive displacement pump and have plenty of fuel pressure beyond the factory filter. Actually I dont even use the factory fuel filter as a main filter. If I unscrew the bleeder on top of the factory filter fuel is squirting out. There is no vacuum needed to pull up the fuel I have a supply pump.

Does anyone know any relevant first steps for diagnosis for my problems which again are: (no supply problem!) hard to no start due to low rail pressure when cranking (less then 1400 psi), knocking number 7 injector, unable to produce pressure beyond 13k with Tech 2 commanded 22k psi. Thanks Nick
 

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Knowing that a lift pump was installed would've prevented my response above.
Is it the original FPRV?

My '05 5500 came home on the hook several times...leaking FPRV, bad fuel tank sender, injector connectors 2&7. All before 70k miles.

I have 5 lly trucks, and one injector in 1.2 million miles.
One FPRV valve.
One FPR...this one had symptoms like yours, hard start, worse warm, poor driveability sometimes.
 

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Is it the original FPRV?
One FPRV valve.
One FPR...this one had symptoms like yours, hard start, worse warm, poor driveability sometimes.
Cab chassis and medium duty come with a factory lift pump.
I agree with the FPR as a good place to start, had this same issue on my 03 truck and FPR cured the problem. Since you have the pump on your truck, would not worry about an air leak at the filter head, you will see fuel sweat or a leak if that is the case. Could be the CP3 but that is usually not the issue, tough pump and very reliable. Injector leak down could be part of the problem but FPR is first place I would look.
Good luck and let us know what you find.
 

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I dont believe the trucks came with a factory lift pump, at least none that I am aware of . There is a transfer pump between the tanks, but no additional lift pump. Of course, maybe some models were ordered with these.
 
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