Four Of The Most Common Issues With The LBZ Duramax Engine (According To Owners)

General Motors' LBZ Duramax Engine is one of the most reliable engines ever built. Over the years, the LBZ and other Duramax engines have carved out a reputation for durability, reliability, and long service lives. The LBZ Duramax engine was only produced in 2006 and 2007, but in what may be a testament to its longevity, many are still on the road and are highly sought after by enthusiasts.

Still, nothing's perfect, and even the best engines will have problems from time to time. We've decided to compile a list of the most common problems faced by Duramax LBZ owners, based on posts those owners have made online. To put this article together, we've scoured the main forums and message boards Duramax owners go to discuss their vehicles, components, and common problems they are facing.

It is worth noting that this is purely a list of problems that are frequently mentioned in online discussions about Duramax LBZ issues. In 2017, the two millionth Duramax engine was assembled. So forum members — especially active forum members — represent a small fraction of Duramax owners. Posts regarding LBZ issues are an even smaller fraction of those posts. So a problem making this list doesn't mean it's something you may actually encounter. We're still talking about one of the most reliable engines ever built.

Earlier Duramax trucks were plagued with fuel injector issues. However, the common consensus is that General Motors rooted out the problems with the LB7, an earlier model of Duramax, and different injectors were used in the LBZ anyway. Despite this, several Duramax specific and truck enthusiast forums feature threads from owners claiming they have encountered injector issues with their vehicles, or being of the belief that injector issues are common on the LBZ Duramax as they were on previous engines. 

It's worth noting that these posts are countered by other owners claiming they have had no problems, and by a number of mechanics that say the Duramax LBZ isn't known for its injector issues. No matter how reliable the engine, faulty parts will still exist. The fact it was an issue on the LBZ's predecessors may make some owners think the problem is bigger than it is, and reputation may have earned the Duramax LBZ's fuel injectors a spot on this list. Either way, fuel injector issues are amongst the most common problems Duramax LBZ owners have listed online.

An underperforming fuel pump leading to fuel starvation is an issue that has plagued many Duramax engines for years. The problem seems to have first been flagged back in 2001, and continued up until 2016, with the LBZ Duramax engine being built right in the middle of that timeframe. So yes, fuel issues — including not enough fuel making it to the injectors, air in the lines, and problems bleeding the system — were all present in the LBZ Duramax.

The problem seems to be the use of a mechanical fuel pump to draw from the tank and deliver it to the injection tank. The addition of a low pressure lift pump solves these problems. Small cracks in the fuel filter housing can also lead to air in the system. If your engine is struggling to start or seems down on power, some Duramax LBZ owners — and Duramax owners in general — will quickly point towards air in the fuel lines. Replacing the housing and bleeding the system could solve your truck's problems.

The LBZ solved a lot of problems that plagued previous Duramax engines, but one notable issue did carry over from its LLY predecessor. A fault with the glow plug module would cause the glow plugs to cycle excessively. This can make them brittle, and eventually cause them to fail. Unfortunately, this is one of those problems where the part simply not working is the least of your worries. Due to the glow plug's location in the engine, a brittle glow plug is likely to shatter into the engine's cylinder. Those bits of glow plug could then go on to cause catastrophic damage throughout the engine.

Multiple forum users report going through excessive numbers of glow plugs in a short span of time. This is an obvious clue that there is a problem, and the glow plug module is an obvious place to look. While you may see a bad batch of glow plugs causing a similar problem, multiple failures over a span of time and involving glow plugs from different batches indicates the fault lies elsewhere.

The issue is fixed by replacing or reprogramming the glow plug module that is at fault. If you're not comfortable with altering bits of your car's software, or you don't have the tools available to do so, then replacement is likely your best option when attempting the repair yourself. You can also temporarily go without glow plugs. In most regions, glow plugs aren't vital to a diesel engine's function, but do make starting it a lot easier — especially in colder climates.

When GM was designing the LBZ Duramax, it decided to manufacture the pistons from cast aluminum. Thinner wrist pins and wrist pin bushings were also used, and the redesigned rotating assembly solved the connecting rod issues that had previously plagued LB7 and LLY engines.

Normally, these design choices wouldn't be too much of an issue. The LBZ was designed with a lower compression ratio in mind, so the pistons wouldn't be dealing with excessive force if used as the designers originally intended. However, the LBZ has a reputation for being one of the most tunable truck engines ever released, and true enthusiasts really love to tinker. Pushing for more power from the LBZ may put more strain on the pistons than they can handle, and there are various complaints about those aluminum pistons cracking. It's fair to say that piston issues are the problem that is most closely associated with the Duramax LBZ.

The solution isn't exactly simple, but it is pretty obvious. If you own a Duramax LBZ, and want to tune it, you should replace its aluminum pistons with more durable aftermarket pistons that are capable of dealing with the extra force.