DIY Duramax Fuel Fix for Leaky Filters

A common problem with high-mileage 2001-2010 Duramax trucks is that the fuel filter head assembly begins to develop air leaks. The engine’s CP3 high-pressure fuel pump is capable of drawing fuel from the tank without the aid of an external lift pump as long as the system remains primed. With age as well as use of ULSD and bio-diesel fuels, the O-rings in the filter head assembly can begin to allow air to bleed into the system, causing the fuel system to loose its prime.

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Early signs of a leak include extended cranking after the truck has been sitting for long periods as well as the engine starting and then dying. As the problem worsens, it may become impossible to restart the truck without manually priming it when parked on an incline. External fuel leaks can develop as well, and will be evidenced by fuel puddles on the ground or on top of the filter assembly.

If you have a high-mileage Duramax-powered truck and suspect that it’s losing its prime, or you have seen evidence of fuel leaks from the filter head, you’ll want to address the problem as soon as possible. Your GM dealer will most likely suggest replacing the entire assembly, but the team at Merchant Automotive has better (and less expensive) solutions: they have developed several repair kits that require only hand tools and basic mechanical skill. The kits start at around $20 for replacement O-rings and go up to around $100 for the Master Filter Head Kit that includes new O-rings, billet aluminum water-in-fuel (WIF) plug, billet aluminum filter head spacer kit, billet aluminum bleeder screw and an OEM replacement fuel filter.

Remember, this is an overview of the process; if you have questions about the specifics you can consult the team at Merchant Automotive or your local diesel performance shop. You can also watch a video of the process on the Merchant Automotive website. If you plan to rebuild the filter assembly yourself, set aside a couple hours and be sure to practice safe shop techniques. After rebuilding and reinstalling the filter assembly you will need to prime the fuel system before starting the truck. Prime the system by pumping the primer plunger repeatedly until it becomes firm, and then start the engine. After starting, make a thorough check for fuel leaks before driving the truck.

The billet aluminum parts in the Master Kit look good, but they aren’t just there for looks. A billet aluminum bleeder screw replaces the factory-installed plastic bleeder screw, which is flimsy and prone to stripping and cracking. The replacement water-in-fuel plug replaces the factory part with its easily broken harness, and the spacer locates the filter assembly an additional 3/8-inch away from the engine to make it easier to replace. All of the billet aluminum parts are anodized black for durability and good looks, and they feature a laser-etched MA logo. You can rebuild your fuel filter assembly without the billet parts, but we think the full kit is a wise investment.

We followed along with shop technician Jake Phaff as he rebuilt the filter head on a customer’s LB7 Duramax. Phaff removed the filter assembly, rebuilt it and reinstalled it in about an hour, including our typical photography slowdowns. Follow along over the next few pages to see the basics of Phaff rebuilding the filter head assembly. DW

1. Merchant Automotive's Master Filter Head Kit includes everything seen here as well as a new OEM fuel filter.

1. Merchant Automotive’s Master Filter Head Kit includes everything seen here as well as a new OEM fuel filter.

2. The filter assembly on this truck was not leaking fuel externally, but it was allowing air to bleed back into the fuel system causing the CP3 to loose its prime. The truck would not start unless the fuel system was manually primed.

2. The filter assembly on this truck was not leaking fuel externally, but it was allowing air to bleed back into the fuel system causing the CP3 to loose its prime. The truck would not start unless the fuel system was manually primed.

3. Jake Phaff began the installation by removing the passenger-side intercooler tube to make it easier to access the fuel filter assembly.

3. Jake Phaff began the installation by removing the passenger-side intercooler tube to make it easier to access the fuel filter assembly.

4. With clear access to the fuel filter assembly, Phaff loosened the spring clamps on the fuel lines and slid the lines off the fittings.

4. With clear access to the fuel filter assembly, Phaff loosened the spring clamps on the fuel lines and slid the lines off the fittings.

5. Moving to the wheel well, he removed the fasteners from the forward portion of the inner fender liner, and then pulled the liner back to allow him easy access to the underside of the fuel filter assembly.

5. Moving to the wheel well, he removed the fasteners from the forward portion of the inner fender liner, and then pulled the liner back to allow him easy access to the underside of the fuel filter assembly.

6. Both the water-in-fuel sensor harness and the fuel heater harness must be unplugged before the filter assembly can be removed from the engine.

6. Both the water-in-fuel sensor harness and the fuel heater harness must be unplugged before the filter assembly can be removed from the engine.

7. With everything disconnected, Phaff was able to unbolt and remove the complete filter assembly from the truck.

7. With everything disconnected, Phaff was able to unbolt and remove the complete filter assembly from the truck.

8. Looking at the water-in-fuel sensor harness, it was obvious that it was ready to fail (see arrow). In fact, when positioning the harness for our photos, the corroded lead actually broke away from the sensor.

8/9. Looking at the water-in-fuel sensor harness, it was obvious that it was ready to fail (see arrow). In fact, when positioning the harness for our photos, the corroded lead actually broke away from the sensor.

8/9. Looking at the water-in-fuel sensor harness, it was obvious that it was ready to fail (see arrow). In fact, when positioning the harness for our photos, the corroded lead actually broke away from the sensor.

10. Before rebuilding the head, the filter and WIF sensor need to be removed from the head. Be careful as fuel can spill from the filter when it’s removed. Be sure to dispose of remaining fuel properly.

10. Before rebuilding the head, the filter and WIF sensor need to be removed from the head. Be careful as fuel can spill from the filter when it’s removed. Be sure to dispose of remaining fuel properly.

11. With the filter removed, Phaff removed the screws securing the heater assembly with a T-20 Torx bit.

11. With the filter removed, Phaff removed the screws securing the heater assembly with a T-20 Torx bit.

12. He then disconnected the heater power lead and pushed the heater assembly out of the filter head, making sure not to loose the spring or check ball in the process.

12. He then disconnected the heater power lead and pushed the heater assembly out of the filter head, making sure not to loose the spring or check ball in the process.

13. Next, Phaff removed the Torx screws securing the plunger to the filter head, noting the position of the fuel heater ground lead.

13. Next, Phaff removed the Torx screws securing the plunger to the filter head, noting the position of the fuel heater ground lead.

14. The cap, retainer, primer and spring could now be removed from the head.

14. The cap, retainer, primer and spring could now be removed from the head.

15. Using a pick tool, Phaff removes the old O-rings from the fuel heater, filter head and primer assembly. If you don’t have a pick tool, you can use a toothpick or other similar pointy object.

15. Using a pick tool, Phaff removes the old O-rings from the fuel heater, filter head and primer assembly. If you don’t have a pick tool, you can use a toothpick or other similar pointy object.

16. After the filter head is completely disassembled, Phaff cleans it with a steady stream of brake cleaner to dislodge any dirt or debris that may have accumulated over the years in order to make sure it does not get inside the fuel system during reassembly.

16. After the filter head is completely disassembled, Phaff cleans it with a steady stream of brake cleaner to dislodge any dirt or debris that may have accumulated over the years in order to make sure it does not get inside the fuel system during reassembly.

17. The replacement O-rings from the kit are installed next. They must be fully seated and not twisted, and lubricated with a small amount of clean engine oil so they will slide into position during assembly without snagging and getting damaged.

17. The replacement O-rings from the kit are installed next. They must be fully seated and not twisted, and lubricated with a small amount of clean engine oil so they will slide into position during assembly without snagging and getting damaged.

18. When installing the new O-rings on the plunger section, the lips of the O-rings must face away from each other as shown here.

18. When installing the new O-rings on the plunger section, the lips of the O-rings must face away from each other as shown here.

19. The plunger assembly is reinstalled on the top of the filter head with the fuel heater ground lead in the same position as when it was removed.

19. The plunger assembly is reinstalled on the top of the filter head with the fuel heater ground lead in the same position as when it was removed.

20. Phaff replaced the flimsy plastic fuel bleeder with the new billet aluminum bleeder included in the Master Kit.

20. Phaff replaced the flimsy plastic fuel bleeder with the new billet aluminum bleeder included in the Master Kit.

21. Pumping the primer with a finger covering the inlet port tests the new O-ring seals; it should develop a vacuum. If it does not, one of the O-rings may be missing or cut.

21. Pumping the primer with a finger covering the inlet port tests the new O-ring seals; it should develop a vacuum. If it does not, one of the O-rings may be missing or cut.

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22/23. After verifying that the seals are working well within the rebuilt filter head, Phaff installs the billet aluminum WIF plug using an MA WIF wrench. It can also be installed with a 3/8-inch square-drive ratchet using a machined recess in the plug. He then installed the filter on the filter head. When doing this job, be sure to install the O-ring for the filter, otherwise you’ll end up with a big mess on your garage floor.

22/23. After verifying that the seals are working well within the rebuilt filter head, Phaff installs the billet aluminum WIF plug using an MA WIF wrench. It can also be installed with a 3/8-inch square-drive ratchet using a machined recess in the plug. He then installed the filter on the filter head. When doing this job, be sure to install the O-ring for the filter, otherwise you’ll end up with a big mess on your garage floor.

24. Phaff installs the complete assembly on the engine using the longer mounting bolts supplied with the kit. He starts each bolt into the threads in the filter head, leaving room for the spacer to be installed.

24. Phaff installs the complete assembly on the engine using the longer mounting bolts supplied with the kit. He starts each bolt into the threads in the filter head, leaving room for the spacer to be installed.

25. After installing the spacer, the bolts are fully tightened to secure the filter assembly to the engine.

25. After installing the spacer, the bolts are fully tightened to secure the filter assembly to the engine.

26. The next step is to reinstall the inlet and outlet fuel lines and slide the clamps into position to secure the fuel lines.

26. The next step is to reinstall the inlet and outlet fuel lines and slide the clamps into position to secure the fuel lines.

27. Moving back down to the wheel well, Phaff plugs in the fuel heater harness and secures the WIF harness before reinstalling the inner fender liner.

27. Moving back down to the wheel well, Phaff plugs in the fuel heater harness and secures the WIF harness before reinstalling the inner fender liner.

28. To complete the installation the fuel system needs to be primed again by pumping the plunger on top of the filter head then purging the air from the system through the bleeder screw. This process may need to be repeated a few times to get all of the air out of the system. After starting the truck, check for leaks before driving.

28. To complete the installation the fuel system needs to be primed again by pumping the plunger on top of the filter head then purging the air from the system through the bleeder screw. This process may need to be repeated a few times to get all of the air out of the system. After starting the truck, check for leaks before driving.

SOURCE:

Merchant Automotive

866.399.7169

Merchant-Automotive.com