Changing Fuel Injectors In A Duramax Diesel: Step-By-Step Guide

Changing the fuel injectors in a Duramax diesel engine can be a challenging task, but with the right tools and knowledge, it is certainly achievable. The process involves removing the intake, fuel filter, housing, and lines, as well as disconnecting various computer hardware and electrical connections. One must also take care in handling the injectors themselves, as they are sensitive and can be easily damaged. It is recommended to use only brand-new Bosch injectors for replacement, as they have a reputation for quality and longevity. Additionally, it is important to clean the injector bores and ensure proper sealing with new copper washers and O-rings. The reassembly process is essentially the reverse of disassembly, and one must take care to torque the injector hold-downs to the specified 37 ft-lb. While challenging, changing the fuel injectors in a Duramax diesel can be a rewarding experience for those with the necessary skills and patience.

Tools and parts needed

The tools and parts required to change the fuel injectors in a Duramax diesel engine will vary depending on the specific model and year of your vehicle, as well as the extent of the repair or replacement work needed. Here is a detailed list of tools and parts you will need to get started:

Tools:

• Basic set of metric tools
• 5mm allen bit, wrench, and ball end bit
• 8mm allen bit or ball end bit
• Torque wrench
• 19mm wrench, stubby, crows foot
• Pick set
• Pry bar set
• Floor jack
• 8mm socket
• 12mm, 17mm, 19mm wrenches
• 10mm, 11mm, 12mm, 13mm, 15mm sockets/ratchet
• Flat-head screwdriver
• Injector puller
• Drill
• Coat hanger
• Shop rag

Parts:

• Fuel injectors (ensure you purchase brand-new, high-quality injectors, preferably from a reputable brand such as Bosch)
• Fuel injector installation kit (including banjo washer pairs, external injector o-rings, and copper seat washers)
• RTV silicone sealant (e.g., Permatex Ultra Grey)
• Copper washers and o-rings (ensure these are replaced with new ones during installation)
• Fuel filter
• Coolant (it is recommended to drain the coolant before starting the repair to avoid any leaks)
• Lubricant (e.g., motor oil)
• Fuel line bolts (it is recommended to replace these with new ones if the old ones are stripped)

Removing tubing, intake, and brackets

To remove the tubing, intake, and brackets, start by removing all the tubing on the passenger side. Then, remove the intake tubing, the MAF connector, and the brackets over the injector. These brackets are 12mm, but the bottom bracket holds the electrical connector for the injector, so be sure to unclip that and push it out of the way.

Next, disconnect the fuel hose and the brackets covering the injector closest to the firewall. If you have already drained the coolant, you can take the driver-side upper coolant tube off for easy access to the fuel rail. If you have an EGR, you will need to remove the hot-side intercooler pipe, disconnect the two big wire harness connectors, and remove their holding bracket (2-12mm nuts and a 13mm bolt).

Now, remove the main computer (the fuel injection control module or FICM) and its mount, as well as tons of rubber and electrical connections. Only remove what you need to minimize the possibility of a crossed hose or line during reassembly.

With the main computer out of the way, the injector line from the common rail to the injector line is finally exposed. You will still need to remove the upper and lower valve covers to access the injectors.

To remove the upper valve cover, there are tabs sticking out that you can use as pry points. The factory sealant is very strong, so you may need to use a pry bar set. You can also pull the alternator off and use the bracket as a fulcrum for more leverage against the valve cover.

With the upper valve cover off, remove the electrical connections to the injectors. As these wires lead a very hard life, it is a good time to inspect them for any damage.

To remove the lower valve cover, you first need to disconnect and remove the injector wire harness. It is held down to two injectors with four 7mm nuts and two gold 10mm bolts. The 7mm nuts are permanently fixed to the harness, so you don't need to worry about losing them, just the 10mm bolts.

With the lower valve cover off, remove the injector return line. Be careful with this, as these bolts strip easily.

Now, all the injectors have a bracket holding them in place. Unscrew them (they are pretty tight), and then, to pop the injectors out, give them a little twist first to make sure they aren't stuck to the cup. Then, use a small pry bar to pop them out from the top, using the bottom of the high-pressure supply line on the injector as a pry point and the head bolt as your fulcrum.

Finally, before removing the brackets, be sure to remove the copper washer from the bottom of the cup if it doesn't come out with the injector. Also, be sure not to lose the steel button that rests under the bracket that holds down the injector.

Disconnecting wires and removing valve covers

Disconnecting Wires:

• Start by removing the intake tubing, MAF connector, and any brackets or hardware covering the injectors.
• Disconnect the electrical connectors from the injectors. These wires can be damaged due to their location, so it is important to handle them carefully and inspect them for any signs of wear or damage.
• For the driver's side, you will also need to remove the hot-side intercooler pipe, disconnect the wire harness connectors, and remove their holding bracket. Additionally, disconnect the fuel hose and any brackets covering the injector closest to the firewall.

Removing Valve Covers:

• To access the valve covers, you will need to remove the fuel filter housing and lines. This will provide the necessary clearance to work on the valve covers.
• The fuel injection control module (FICM) is typically mounted on the passenger-side valve cover, so it will need to be removed as well. Be sure to also remove its mount and any associated rubber and electrical connections.
• With the main computer out of the way, carefully remove the upper and lower valve covers. The upper valve cover can be especially challenging to remove due to the strong factory sealant. You may need to use a pry bar or similar tool to carefully lift it off.
• Once the upper valve cover is removed, you will have access to the injectors. Be sure to clean the upper valve cover and inspect it for any damage before reinstallation.

Removing and replacing injectors

The first step in the process of removing and replacing injectors is to remove the intake. This will grant access to the fuel filter, housing, and lines, which must also be removed to reach the valve cover.

Next, remove some of the computer hardware, specifically the fuel injection control module (FICM), which is mounted on the passenger-side valve cover. Its mount, as well as rubber and electrical connections, must also be temporarily relocated.

Now, the injector lines are exposed. Remove the upper and lower valve covers to access the injectors.

Remove the electrical connections to the injectors and inspect them for any damage—they lead a hard life.

The next step is to remove the injector return line. Be careful not to strip any of the bolts that secure it. These fasteners can be easily stripped and must be replaced if that happens.

An injector puller is one of the few specialty tools needed for injector extraction. It is available at many tool supply trucks, stores, and online.

After removing the injectors, place the new injectors in the injector cups and secure the hold-downs with the recommended 37 ft-lb of torque.

Now, begin the reassembly process. First, install the fuel rail, along with new bolts if needed.

With the new injectors, electrical connections, and lower valve cover reinstalled, clean the upper valve cover and install it, using grey RTV silicone to ensure a leak-free seal between the head and the cover.

The factory injector lines can often be contaminated with rust, so it is recommended to replace them with new Bosch pieces to avoid wiping out a brand-new set of injectors.

Once the injector lines are in place, reinstall the fuel filter housing and FICM.

The final step before starting the engine involves connecting the engine's air-intake tubing and filter box to the Duramax's turbocharger.

Even with everything connected, the fuel system needs to be primed for the engine to start. This can be done by pressing on the primer on the filter housing, which, after about 20 to 30 pushes, will become hard, signalling it's time for the engine to be fired.

Reassembling and testing

Once you have finished replacing the fuel injectors in your Duramax diesel engine, it is now time to reassemble the engine and test your work.

First, install the fuel rail, along with new bolts if needed. Then, reinstall the electrical connections and the lower valve cover. Next, clean the upper valve cover and install it using gray RTV silicone to ensure a leak-free seal between the head and the cover.

Now, it is time to replace the injector lines with new Bosch pieces. Once the injector lines are in place, reinstall the fuel filter housing and FICM. The final step before starting the engine involves connecting the engine's air-intake tubing and filter box to the Duramax's turbocharger.

Even with everything connected, the fuel system needs to be primed for the engine to start. This can be done by pressing on the primer on the filter housing, which, after about 20 to 30 pushes, will become hard, signalling it is time for the engine to be fired.

With the Duramax started back up, the balance rates of the new injectors should be checked and fall well within spec. Your LB7 is now ready to hit the road for thousands more miles!

Frequently asked questions