Replacing Fuel Injectors: 2004 Duramax Edition

Replacing the fuel injectors on a 2004 Duramax is a complex process that requires a medium level of wrench-turning skills. The first step is to disconnect the battery cables and drain the coolant. On the driver's side, remove the turbo-to-intercooler charge pipe, fuel feed and return lines, electrical connections, and mounting brackets. Disconnect the serpentine belt and unbolt the AC compressor. Remove the thermostat housing and upper radiator hose. Disconnect the fuel connector tubes, unbolt the valve covers, and remove the internal injector harnesses and lower valve cover. Access the fuel return line and remove each injector hold-down bolt. On the passenger side, remove the intercooler-to-Y-bridge tube, air filter, intake, fuel filter head, engine wiring harness, and FICM. With all eight injectors accessible, the process is the same as on the driver's side. After installation, top up the coolant, change the engine oil, add a new oil filter, and start the engine to check for leaks.

How to replace fuel injectors on a 2004 Duramax

Remove the passenger-side wheel, inner fender, and drain the coolant

To remove the passenger-side wheel, inner fender, and drain the coolant, follow these steps:

First, remove the passenger-side wheel. This will give you better access to the inner fender and make it easier to remove the valve cover bolts later on. Loosen the lug nuts before jacking up the vehicle and use a jack stand for safety.

Next, remove the inner fender, which is the black plastic part. This will give you better access to the engine and the components you need to remove or work on.

Now, drain the coolant from the radiator. Place a bucket underneath the drain plug on the bottom passenger side of the radiator. The coolant will shoot out towards the rear of the truck with some force, so be prepared for a mess! Once you've removed the plug, direct the flow of coolant into the bucket.

At this point, you can also unhook the big blue turbo intake hose from the intercooler by loosening the 10mm nut on the clamp and pulling the hose off. Then, remove the turbo intake hose from the top of the engine and set it aside.

By removing the passenger-side wheel, inner fender, and draining the coolant, you'll have better access to the engine and can proceed with the fuel injector replacement process.

Disconnect the turbo intake hose, fuel filter bracket, and FICM

Disconnecting the turbo intake hose, fuel filter bracket, and FICM is a crucial step when replacing fuel injectors on a 2004 Duramax. Here is a detailed guide on how to perform this step:

Disconnecting the Turbo Intake Hose:

To remove the turbo intake hose, start by loosening the clamp around the turbo inlet where it attaches to the turbo. You can then remove the airbox tube. If there is a hard plastic line attached, you may need to unhook it as well. Make sure to have rags or a drip pan handy to catch any fuel that may spill during this process.

Disconnecting the Fuel Filter Bracket:

The fuel filter bracket is located near the alternator. To remove it, first disconnect the air intake elbow and unplug as many sensors as possible to move the wire harnesses out of the way. This will give you more room to work. Next, remove the two fuel hoses attached to the hard lines beside the alternator. Make sure to mark the hoses to remember which hose is which and to ensure that the fuel flows in the correct direction. Once the hoses are removed, you can then remove the two bolts holding the fuel filter and its head to the bracket. Be sure to unplug the WIF sensor before removing the last bolt.

Disconnecting the FICM:

The FICM (Fuel Injector Control Module) is located on the passenger side of the engine. To disconnect it, you will need to remove the FF (fuel filter) bracket, which is held in place by three bolts, and a fourth bolt holding a coolant line. Once the bracket is removed, you can disconnect the FICM connectors by sliding the tabs up and lifting the connectors off. After disconnecting the FICM, you will also need to disconnect the glow plug wire and remove the metal bracket connecting them.

It is important to work carefully and methodically when performing these steps, ensuring that you have the necessary tools and safety equipment, such as gloves and rags, to catch any fuel spills.

Remove the injector lines, upper valve cover, and injector wire harness

To remove the injector lines, upper valve cover, and injector wire harness, start by removing the passenger-side wheel and the inside fender (black plastic). Then, drain the coolant from the radiator by removing the drain plug on the bottom passenger side. This is necessary in case an injector cup comes out with an injector, preventing the cylinder from filling with water.

Next, remove the turbo intake hose from the intercooler by loosening the 10mm nut on the clamp and pulling the hose off. Also, unhook the turbo intake hose from the top of the engine and set it aside. Now, starting on the passenger side, remove all the tubing, intake, the fuel filter bracket (there are three bolts holding it on and a fourth one just holding a coolant line), and the Fuel Injector Control Module (FICM). Disconnect the FICM by sliding the tabs up and down. After disconnecting the engine wire harness, pull it out of the way and start removing the FF and FICM.

Now, disconnect the glow plug wire and move it out of the way. Some LB7s have a wire that goes to each individual glow plug, which will all need to be removed.

Remove the keepers on the high-pressure fuel lines with an 8mm socket or a Phillips-head screwdriver. Then, remove the injector lines with a 19mm wrench.

The next step is 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 long socket as a pry point for a screwdriver, prying up on the lower tab of the valve cover.

To remove the injector wire harness, you will need to disconnect it and remove the four 7mm nuts and two 10mm gold bolts holding it to the injectors. The 7mm nuts are permanently fixed to the harness, so you don't need to worry about losing them, but make sure to keep hold of the 10mm bolts.

Once these steps are complete, you can then move on to removing the lower valve cover.

Loosen the injector return line and remove the injector bracket

To loosen the injector return line, you will need a 5mm Allen bit, a wrench, and a ball end bit. Be careful when removing the bolts as they strip easily. You may need to use channel locks if you damage the bolts.

To remove the injector bracket, you will need a 8mm Allen bit. These bolts are pretty tight, so be careful not to strip them. Once the injector is loose, give it a little twist first to ensure it isn't stuck to the cup. Then, use a small pry bar to pop the injector 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. The injector should pop out easily. Make sure to remove the copper washer from the bottom of the cup if it doesn't come out with the injector. Be sure not to lose the steel button that rests under the bracket that holds down the injector.

Reinstall the injector, return lines, and valve covers

To reinstall the injector, return lines, and valve covers, you will need to follow these steps:

Firstly, before putting the injectors back in, put on two new O-rings. You can see in the picture where the O-rings should be placed. Reinstall a new copper washer at the bottom of the injector cup. Install the injector with the clamp and torque it down to 37 ft-lbs.

Next, reinstall the return lines with new seals. Tighten the banjo bolts to 12 Nm or 106 lb-in. Tighten the 12mm banjo bolt that goes into the head to 11 lb-ft.

Now, install the lower valve cover and tighten the bolts in sequence to 10 Nm or 89 lb-in twice. Then, install the injector harness and tighten the bracket bolts to 9 Nm or 80 lb-in. The 7mm connectors should be tightened to 2 Nm or 18 lb-in.

Finally, put a bead of sealant on the bottom of the upper valve cover, about 2-3mm wide and 1mm high, and install the cover. Tighten the bolts to 8 Nm or 71 lb-in in the specified sequence. Install the injector lines and keepers.

One thing to note upon reassembly is to seal the top of the high-pressure line fitting on the injector end. This keeps dirt and debris from building up and dumping inside the injector. You can also wipe off excess RTV silicone around the upper valve cover to make it neat.

Now put the fuel filter and FICM back on and you're ready to move on to the driver's side.

Frequently asked questions