Ameer Randolph
Testing the fuel pump on a 2008 Duramax diesel engine involves several steps. First, the fuel filter housing should be checked for air leaks, and if present, the fuel outlet line should be removed and capped. Next, the ignition 1 relay should be removed, and the engine cranked for short intervals, with the high-pressure pump pulling at least 12 inches of Hg vacuum. Clear hoses should be installed at the inlet and outlet of the fuel filter housing, and the system re-primed before starting the engine. Additionally, the Enhanced Injector Return Flow Test by GM can be used to test the injectors. This involves running the engine at normal operating temperature, removing return hoses, using adapters to run hoses into graduated containers, and measuring fuel flow. If the return volume is less than expected, a high-pressure pump test is recommended.
| Characteristics | Values |
|---|---|
| Fuel pump issues | Metal shavings in the fuel system, failure of the ceramic part in the pump |
| Fuel filter | Designed to filter down to 5 microns |
| Fuel pressure regulator | Ensure it is not stuck |
| Fuel pressure relief valve | Ensure it is not leaking into the return system when rail pressure is 160 MPa |
| Fuel rail pressure | Runs at 6000-26,000 psi |
| Fuel feed line | Prone to collapsing shut and throwing the p0087 code |
| Fuel vacuum test tool | Prime the fuel system until 10 PSI is indicated on the gauge |
| Injector return flow test | Engine at normal operating temperature, 181-189 deg. F |
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What You'll Learn
Testing for metal shavings in the fuel system
- Prime the fuel system with a hand primer until 10 PSI is indicated on the gauge.
- Check for external leaks and repair if necessary.
- If the pressure drops from 10 PSI to 2 PSI in less than one minute, remove the fuel outlet line from the filter and cap it.
- Remove the ignition 1 relay and crank the engine for 2-15 second intervals. The high-pressure pump should pull at least 12 inches of Hg vacuum.
- Install clear hoses at the inlet and outlet of the fuel filter housing.
- Re-prime the system and then start the engine. There should be very little air going into or coming out of the fuel filter housing.
Another way to test for metal shavings is to perform an Enhanced Injector Return Flow Test, specifically for LBZ engines but applicable to LLY and LMM engines as well. Here are the steps:
- Ensure the engine is at normal operating temperature, between 181-189 degrees F.
- Remove the return hoses from one bank of injectors.
- Use adapters to run hoses off of injector returns into individual graduated containers.
- Run the engine until fuel flows from all four injector return hoses.
- With the engine at idle, command rail pressure to 17,400 PSI with the scan tool. Place the hoses in the graduated containers for 30 seconds.
- Turn off the ignition and record measurements.
- Repeat the above steps on the other bank of injectors.
- Add up all recorded measurements to determine the total injector return volume. If the return volume is less than 144 ml for all 8 injectors, refer to the high-pressure pump test.
Additionally, it is important to check for any signs of fuel contamination, such as water, rust, or accidental contamination with DEF. Fuel contamination can be a cause of fuel pump failure and metal shavings in the system. Regular use of fuel additives can help prevent water contamination and keep the system clean.
It is worth noting that some metal shavings in the fuel filter housing may be considered normal by some mechanics, but it is always best to have it inspected and addressed by a qualified diesel mechanic or a reputable dealer to ensure the issue is properly diagnosed and resolved.
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Using a fuel vacuum test tool
To test a diesel fuel pump on a 2008 Duramax using a fuel vacuum test tool, follow these steps:
Firstly, ensure the fuel filter housing is installed, as the 2008 Duramax does not have a supply pump from the factory, and the fuel filter housing is on the suction side. Prime the fuel system with a hand primer until the gauge indicates 10 PSI. Check for external leaks and repair them if necessary. If the pressure drops from 10 PSI to 2 PSI in less than one minute, remove the fuel outlet line from the filter and cap it. Remove the ignition 1 relay and crank the engine for intervals ranging from 2 to 15 seconds. The high-pressure pump should pull at least 12 inches of Hg vacuum. If air gets into the system, it may cause a false or low reading.
Install clear hoses at the inlet and outlet of the fuel filter housing. Re-prime the system and then start the engine. There should be minimal air going into or coming out of the fuel filter housing.
Additionally, you can install a vacuum gauge, such as the J 44638 Vacuum Gauge, on the fuel fitting located on the right-side front of the engine. Start the engine and run it at idle. Slowly increase the RPM to wide-open throttle (WOT) in park or neutral while observing the vacuum gauge. Check if the vacuum measures less than the specified value through the entire RPM range.
It is important to note that if you have a lift pump, you can crack the bleeder and turn on the pump until pure fuel comes out. You can also pump on the primer about 10 times, then wait 1-2 minutes and pump another 4-5 times.
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Running the LBZ Enhanced Injector Return Flow Test
First, ensure the engine is at its normal operating temperature of 181-189 degrees Fahrenheit. Next, remove the return hoses from one bank of injectors. Utilise adapters to connect hoses from the injector returns to individual graduated containers. Run the engine until fuel flows from all four injector return hoses. Then, with the engine idling, use a scan tool to command rail pressure to 17,400 PSI. Place the hoses in the graduated containers for 30 seconds. Turn off the ignition and record the measurements.
Repeat the above steps for the other bank of injectors. Calculate the total injector return volume by summing up all the recorded measurements. If the return volume is less than 144 ml for all eight injectors, refer to the high-pressure pump test. Conversely, if the return volume exceeds 72 ml per bank, replace any individual injector with a return volume greater than 18 ml.
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Checking the fuel pressure regulator
To check the fuel pressure regulator on a 2008 Duramax, you should first ensure that the engine is cool. Then, locate the regulator—on a 2003 Duramax 6.6-liter turbo diesel, it is located near the fuel pump and injection system.
Next, you will need to remove the regulator and check for any signs of damage or debris, such as metal shavings or fragments, which can be caused by a bad tank of fuel. If the regulator is damaged or contaminated, it will need to be replaced. If the regulator appears to be in good condition, you should then check the fuel pressure relief valve to ensure it is not leaking into the return system when the rail pressure is 160 MPa.
Before condemning the high-pressure pump, it is important to ensure there are no high-pressure fuel leaks. This can be done by capping off the injector rail to isolate the injectors from the return system using the correct cap set, such as EN-47589. If the smoke disappears when you cut out one cylinder at a time using a scan tool, this indicates a fuel leak.
Additionally, you can check the fuel pressure regulator by priming the fuel system and checking for leaks. Install a fuel vacuum test tool and prime the system until 10 PSI is indicated on the gauge. Check for external leaks and repair if necessary. If the pressure drops rapidly, remove the fuel outlet line from the filter and cap it. Remove the ignition 1 relay and crank the engine for 2-15 second intervals—the high-pressure pump should pull at least 12 inches of Hg vacuum. If air gets into the system, it may cause false or low readings.
Finally, reinstall the fuel filter housing and prime the system again. Start the engine and observe the fuel filter housing for any air entering or exiting. There should be very little air movement.
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Testing the heating element
Firstly, it is important to understand the function of the heating element. The heating element is responsible for warming up the fuel before it enters the injection pump. This is crucial because diesel fuel can become too thick to flow properly at low temperatures. The heating element ensures that the fuel remains at an optimal temperature for efficient combustion.
To test the heating element, you will need to access the fuel pump and its associated components. This may require removing certain parts, such as the fuel tank and fuel sender, to gain clear access to the fuel pump assembly. Once you have clear access, you can begin the testing process:
- Disconnect the fuel lines and carefully remove the fuel pump assembly from the fuel tank. Ensure that you have a suitable container to catch any residual fuel.
- Inspect the fuel pump for any signs of damage or wear. Pay close attention to the heating element and the fuel heater, as these components are prone to failure. Look for any signs of burning, discolouration, or physical damage.
- Clean the fuel pump assembly, ensuring that any fuel residue or debris is removed. This step is important to ensure that any blockages or restrictions are cleared, as these can impact the performance of the heating element and fuel flow.
- Reinstall the fuel pump assembly, ensuring that all connections are secure and proper. Refer to the service manual or a qualified mechanic if you are unsure about the correct installation procedure.
- Prime the fuel system by commanding the fuel pump on with a scan tool. This will ensure that the system is pressurised and that any air is purged. Observe the fuel flow through a transparent hose, if possible, to check for any air bubbles, which could affect performance.
- With the engine off, connect a suitable diagnostic tool to the fuel temperature sensor located in the fuel return line on the engine. This tool should be capable of reading the voltage and ground circuit supplied to the sensor.
- Start the engine and allow it to run for a period of time, ensuring that the fuel temperature sensor detects a fuel temperature above the pre-determined value. This value can be found in the service manual or through a qualified mechanic.
- Observe the diagnostic tool connected to the fuel temperature sensor. If the heating element is functioning correctly, the tool should indicate a failure or an error. This is because, when the fuel temperature exceeds the pre-determined value, the Engine Control Module (ECM) will detect this abnormal condition and trigger a diagnostic failure.
- If the diagnostic tool does not indicate a failure or error, it suggests that the heating element may not be functioning correctly. Further diagnostics or replacement of the heating element may be required.
It is important to note that this process may vary slightly depending on the specific tools available and the exact specifications of your 2008 Duramax. Always refer to the service manual or seek assistance from a qualified mechanic if you are unsure about any steps or procedures.
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Frequently asked questions
There are a few ways to test the fuel pump on your 2008 Duramax diesel engine. One way is to use a scan tool to command the fuel pump on, and prime the fuel system until all air is purged. Start and run the engine, and observe the fuel entering a transparent hose. If air bubbles are present, refer to Diagnostic Aids.
Air bubbles in the fuel system could be caused by a faulty fuel pump, or a leak in the fuel lines.
If your fuel pump is not functioning properly, it may be due to a lack of diesel for lubrication, which can cause parts to wear and send metal fragments through the fuel system.
The Duramax engine has a low and high side fuel system. The high side runs at 6000-26,000 psi, and the low side runs under vacuum as the injection pump sucks the fuel from the tank. You can test the pressure using a fuel pressure kit, and refer to the specific psi readings for your model.
