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This generation of Duramax had the distinction of being the first diesel that General Motors outfitted with emissions control systems. The LLY shared much of its internals with the previous generation, but it introduced a variable geometry turbocharger and redesigned injectors.
Near the end of its production, the internals were changed to something closer to the following LBZ engine and it got a small jump in torque.
ProSource Diesel takes a look at the shortest-lived version of the Duramax engine as well as some of its common problems.
Source: Bring a Trailer
Origin Of the Duramax LLY
Halfway through the 2004 model year, General Motors released the second-generation Duramax, called the LLY.
Much of what went into the Duramax LLY matched the LB7, but the new generation brought an improved design for the fuel injectors, plus cleaner emissions and a variable geometry turbocharger.
The horsepower climbed by 10 and the peak torque became available 200 rpm sooner.
The later models of the Duramax LLY added about 80 pound-feet of torque and the internals had more in common with the LBZ engine that followed. Despite the improvements and additional technology, the LLY did have its issues, including problems with overheating.
The LLY is sometimes forgotten as one of the least desirable Duramax engines, but it was actually a very solid engine.
Duramax LLY Specs
The Duramax LLY was produced starting in the middle of 2004 until early 2006. Its design is a 90-degree V8 with cast aluminum heads and six 14mm diameter head bolts per cylinder. The valvetrain is OHV with four valves per cylinder and a single cam.
The injection system consists of Bosch high-pressure common-rail and direction injection with Bosch solenoid injectors.
The Duramax LLY has a 4.06-inch bore and a 3.90-inch stroke. The displacement is 403 cubic inches or 6.6 liters with a compression ratio of 17.5:1. It features a cast iron block, a Garrett GT3788VA turbocharger, and cast aluminum pistons with forged steel rods.
New Variable Geometry Turbo
Variable geometry turbo technology debuted on the Duramax LLY to meet emissions standards and deliver better drivability. It featured precise electric control of the movable vanes and delivered optimum performance at any engine speed.
The Duramax LLY also featured the largest turbo ever offered on a Duramax engine. This means that the LLY had the highest-flowing factory turbocharger.
With good aftermarket tuning, it’s not hard to get big horsepower gains on any Chevy or GMC HD truck with a Duramax LLY.
Redesigned Injectors
The LB7 had widespread injector issues, so GM redesigned the injectors for the LLY to make them externally serviceable. This solved issues with leaking injectors and cracked injectors. Most well-maintained LLY fuel injectors last between 150,000 and 200,000 miles.
Fuel quality issues and air in the system thanks to the lack of a factory lift pump can sometimes cause injector issues to crop up earlier. But the LLY far outshone the LB7 in this area.
Emissions Systems
Exhaust gas recirculation (EGR) started making an appearance on the LB7 Duramax engines that were sold in California. However, the LLY included the EGR system right from the start, making it legal in all 50 states.
A catalytic converter was added downwind of the turbocharger as well. Neither the EGR nor the cat were particularly prone to failure, but it can happen with higher mileage.
Common Problems With the Duramax LLY
The Duramax LLY wasn’t in production for very long, and what worked went into the next LBZ engine, but some of its problems were carryovers from the previous LB7 engine. The biggest problem with this engine was its tendency to overheat, especially when towing.
It inherently ran warmer than the LB7 engine, in part due to the smallest radiator ever offered with a Duramax.
Source: real-man-truckworks-and-survival.com
Another culprit in the Duramax LLY running warmer than the previous Duramax is the factory turbo inlet manifold, which was highly restrictive and created a chokepoint. This caused the turbo to work harder, which led to hotter exhaust gas and intake air.
Owners of the LLY can resolve this by replacing it with an aftermarket turbo mouthpiece. It’s one of the easiest ways to make your LLY run cooler.
Thanks to its large turbo, the Duramax LLY generated more drive pressure and heat, which led to higher coolant temperatures and took a toll on the head gaskets. Because of that, head gasket failure is fairly common on the LLY.
What Year Was the Duramax LLY?
The Duramax LLY was introduced in the middle of 2004 and was produced through early 2006. Considering that it came out in the middle of 2004, it’s possible to have a GM truck from that period with either the LLY or the previous LB7.
If you’re not sure which one you have, you can check the 8th digit of your truck’s VIN to find out. If the 8th digit of your truck’s VIN is a 2, then you have the Duramax LLY.
How Many Miles Will the Duramax LLY Last?
As with many diesel engines, the Duramax LLY can be quite durable with an average lifespan of around 200,000 miles. With good maintenance and the replacement of some weak factory parts, the Duramax LLY can last up to 500,000 miles.
How Much Horsepower Does the Duramax LLY Have?
Most versions of the Duramax LLY produced 310 horsepower at 3000 RPM and 520 pound-feet of torque at 1600 rpm. The early 2006 models produced 605 pound-feet of torque at 1600 rpm.
Rely on ProSource Diesel to find all the parts you need for the Duramax LLY. Whether you need a new turbo inlet manifold, a new turbo, or one of the many aftermarket parts for the LLY, we have you covered.
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The post Guide to the 2004.5-2005 Duramax LLY appeared first on Prosource Diesel.
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