Photo 2/31 | 001 Lb7 Duramax Fuel Injector Install | LB7 injectors are known as the most troublesome of all Duramax injectors. Fortunately, throughout its years of service, Bosch continually improved the design of the LB7’s fuel injectors. And when combined with the knowledge the aftermarket has accumulated, what we’re left with is a unit that is far more reliable today than when first introduced. Still, even the best LB7 injectors are said to need servicing after about 100,000 miles.
Photo 3/31 | 002 Lb7 Duramax Fuel Injector Install | What was delivered from Dynomite Diesel Products was nothing short of beautiful. Like kids on Christmas, we enjoyed opening each and every one of the individual boxes, even though we knew what was inside.
Photo 4/31 | 003 Lb7 Duramax Fuel Injector Install | There’s no mistaking a DDP injector. The company’s logo is laser-etched into the body.
Photo 5/31 | 004 Lb7 Duramax Fuel Injector Install | Inside the box is everything needed to install the new injectors. They come with two O-rings, a copper washer, and a return tag for your old core.
Photo 6/31 | 005 Lb7 Duramax Fuel Injector Install | It’s important to remember to install the two O-rings. One goes on the injector body and the other on the high-pressure fuel inlet. You’ll want to lube the body O-ring with clean oil before dropping it into the cup.
Photo 8/31 | 007 Lb7 Duramax Fuel Injector Install | Also critically important is the copper washer that sits between the injector cup and nozzle. Carefully drop the washer into the bore and ensure it is sitting flat at the bottom before proceeding.
Photo 10/31 | 009 Lb7 Duramax Fuel Injector Install | The injector hold-down serves the purpose of both locating the injector in the cup and keeping it in place. Make sure these are aligned properly, as they only go one way.
Photo 11/31 | 010 Lb7 Duramax Fuel Injector Install | Next, carefully align the injector with the cup and lower it down into the bore. It’ll take a little pressure to get the O-ring seated, and you’ll feel the positive engagement when it happens. There are specialty tools available to aid in holding both the injector and hold-down clamp, however, we found it easy enough to do without.
Photo 13/31 | 012 Lb7 Duramax Fuel Injector Install | With one bank of injectors installed, we proceeded to torque the brackets to the required 37 ft-lb. It’s important to torque these bolts properly, as too little torque can cause the bolt to back out and the injector to come loose from the cup—and too much can damage the aluminum head.
Photo 14/31 | 013 Lb7 Duramax Fuel Injector Install | After installing the injectors, the return lines can go on. The fuel returns use a banjo bolt that threads into the injector body and special washers to keep them sealed. We replaced these washers with new units from Merchant Automotive.
Photo 15/31 | 014 Lb7 Duramax Fuel Injector Install | Another failure point is the banjo bolt itself. The factory bolts (left) have a shallow head and are known to strip after even just one use. Merchant Automotive offers replacement bolts (right) with significantly deeper heads, allowing the 5mm Allen wrench enough purchase to not immediately destroy the bolt.
Photo 16/31 | 015 Lb7 Duramax Fuel Injector Install | We found it easiest to install all four bolt and washer sets before lowering the return line into place.
Photo 17/31 | 016 Lb7 Duramax Fuel Injector Install | The return bolts are torqued to 12 ft-lb—no more, no less. A good 3/8-inch-drive 5mm Allen socket pays dividends when working on a Duramax engine, as a lot of factory bolts utilize that size fastener.
Photo 18/31 | 017 Lb7 Duramax Fuel Injector Install | Once the injectors and return lines are torqued into place, it’s time to replace the valve cover. On LB7 engines, the injectors live below the cover. The valve covers were redesigned on the LLY and subsequent Duramaxes to move the injectors outside the covers. We used new ARP stainless-steel fasteners to affix the valve covers to the heads, because why not.
Photo 19/31 | 018 Lb7 Duramax Fuel Injector Install | Another issue that plagues LB7 engines more than any other is corrosion inside the high-pressure fuel lines. Often impossible to see with the naked eye, this decay is caused largely by water and other impurities in diesel fuel. Using a bore scope, we’re able to see just how bad the inside of our factory lines was. If any of these particles were to come free, it could easily clog the small orifices within the injector, leading to poor performance and costly repairs.
Photo 21/31 | 020 Lb7 Duramax Fuel Injector Install | Fortunately for us, Dynomite also offers replacement high-pressure lines. These lines are brand-new. They are not refurbished old lines or cheap knockoffs (which do exist on sites like eBay). It’s imperative to get quality lines from a reputable source, since the knockoffs oftentimes cause more problems than the old dirty lines would have. It’s universally recommended to replace these high-pressure lines whenever the injectors are removed.
Photo 22/31 | 021 Lb7 Duramax Fuel Injector Install | The high-pressure fuel lines slip through a grommet in the upper valve cover and onto the injector. Each line is specific to a cylinder, so if it doesn’t fit, don’t force it. Stop and find the correct one. We also chose to replace the valve cover grommets at this time, ensuring many years of leak-free operation.
Photo 23/31 | 022 Lb7 Duramax Fuel Injector Install | Tightening is handled by a ¾-inch open-end or pipe-nut wrench. These nuts should be tightened firmly, but not so much as to damage the injector or fuel rail. The official torque spec is 30 ft-lb.
Photo 24/31 | 023 Lb7 Duramax Fuel Injector Install | With all four high-pressure lines in place, the final step is to install the retaining clips. The operation is repeated on the other bank.
Photo 25/31 | 024 Lb7 Duramax Fuel Injector Install | On LB7 injectors, Dynomite changes out the needle adjustment puck, idle adjustment valve, and spring.
Photo 26/31 | 025 Lb7 Duramax Fuel Injector Install | Needles used receive a diamond-like carbon (DLC) coating to ensure smooth operation and a long life.
Photo 27/31 | 026 Lb7 Duramax Fuel Injector Install | Here, we see the inside of the injector nozzle before being honed.
Photo 28/31 | 027 Lb7 Duramax Fuel Injector Install | And here is the “after” shot. Note the radiuses on the orifice edges and the polish to the nozzle bore.
Photo 30/31 | 029 Lb7 Duramax Fuel Injector Install | Notice the PPE race valve (right) is a solid piece of machined stainless steel, while the factory fuel pressure relief valve (left) has a hole in the middle leading to the spring-loaded valve within.
Photo 31/31 | 030 Lb7 Duramax Fuel Injector Install | On LB7 engines, the fuel pressure relief valve is located on the fuel distribution block mounted to the driver-side intake manifold. LLY, LBZ, and LMM engines (along with 6.7L Cummins engines) have the valve located within the fuel rail. None of which are particularly easy to access.