Diesel Resource | Your go-to diesel experts

What Are The Most Common 6.6L LB7 Duramax Problems?

The LB7 Duramax engine made its debut on Chevrolet and GMC HD trucks in 2001. These diesel engines are where the Duramax started, and they have been so successful that the Duramax are still used in GM HD trucks today. As successful as the 6.6L LB7 Duramax was however, they do have their fair share of problems.

The first Duramax was far from perfect. As with anything brand new, there were some kinks that needed to be worked out. That doesn’t mean the LB7 Duramax isn’t a great truck though. With some aftermarket solutions, you can fix most of the 6.6L LB7 Duramax’s most common problems. Here is our guide to the 7 most common 6.6L LB7 Duramax problems and how to fix them.

1. LB7 Duramax Injectors

The most notorious LB7 Duramax problem is their original injectors. Even GM acknowledged their problems when they corrected the original injector design and issued a 200,000 or 7-year warranty on the updated model. That doesn’t mean the LB7 Duramax you own has this problem corrected though. If you recently purchased your LB7 and it has lower mileage, it could still have the original injectors. If you don’t know the original owner, i’d recommend looking through the paperwork you received when you bought it, or you can look up it’s service history online. When you pull up a vehicle’s Carfax, you can often also see it’s service history and get information on any major mechanical overhauls.

Original LB7 Duramax Injector Flaws

What exactly were the issues of the original LB7 Duramax injectors? Well, for starters, the injectors themselves are vulnerable to cracking. This can occur at anytime on the injector bodies themselves. The ball seat inside the injector can also become faulty over time. The ball seat can deteriorate over time, resulting in an incomplete seal, and ultimately, injector leaking. Both of these issues result in fuel leaking from the injector which can then enter the crankcase. This can lead to more serious problems, as diesel fuel doesn’t offer the same lubrication properties as oil. You’ll also experience loss of power, excessive smoke, rough idling, and engine misfiring.

Signs of Bad LB7 Duramax Injectors

Here are common issues experienced when you have bad injectors.

• Excessive/Constant Smoke when Idling
• Hard Starts
• Fuel in Oil. Check Dipstick look for a surplus of oil or even smell the dipstick. When fuel is present, you can often smell it.

How To Fix Bad Injectors

Unfortunately, there is no good way to fix the factory LB7 Duramax injectors other than replacement. When you’ve found a faulty injector, it needs to be replaced and unfortunately, it isn’t cheap. For that reason, it makes sense to go ahead and replace all of the injectors, even if you’re not having problems with all of them. Most shops will charge you 10-16 hours of labor with a total injector overhaul costing over $3000 after paying for parts, labor, and taxes.

Replacement of LB7 injectors takes a long time because the injectors are located underneath multiple vehicle components. It’s often too difficult for a novice mechanic and should be left for more experienced diesel mechanics. While you’re working on your LB7 you may want to think about replacing the fuel injection lines as well. These lines can become contaminated and cause fuel quality issues.

LB7 Duramax Injectors

2. Lack Of A Fuel Lift Pump

The 6.6L LB7 Duramax uses a high pressure common rail fuel system with direct injection. A major part of this fuel injection system is the CP3 fuel injection pump. While the CP3 has proven itself as reliable, it’s not only responsible for pressurizing the fuel before it’s sent to the injectors, but also for drawing fuel from the tank.

This lack of a fuel lift pump puts some extra strain on the CP3 injection pump. Despite this, issues are still not very common with the actual pump when used with stock applications. When you add some tuning or other performance modifications however, the lack of a lift pump begins to reveal itself, and problems begin to surface.

Lift Pump Problems

The lack of a lift pump means the CP3 injection pump has to work extremely hard to pressurize fuel as well as suction fuel from the gas tank. In higher horsepower applications, a loss of fuel rail pressure while accelerating can occur. Even in stock applications, this design is also more likely to encounter air in the fuel lines.

Fixing The Problem

The only way to fix the problem is to add a lift pump! Even a stock truck can benefit from the addition of a fuel lift pump. They can greatly improve the life span of your fuel system components like injectors or your CP3 injection pump. They also improve performance and reduce emissions!

You have to be careful when selecting one however. If you’re driving a stock truck, you should select a unit that offers flow of 100 gallons per hour or less. For higher horsepower applications, you can purchase up to 160 gph or higher, all depending on your needs.

Benefits of a Lift Pump System

• Improved Fuel Economy
• Better fuel filtration and water separation
• Increased fuel system life, including: Injectors, CP3 injection pump, and more.
• Improved throttle response
• Reduced emissions

Lift Pump Systems We Recommend

Air Dog II 4G 100 GPH Flow

For stock applications, Air Dog makes the Air Dog II 100 GPH Air/Fuel Filtration system. This lift pump is ideal for stock trucks or slightly modified trucks up to 500 horsepower.

• Photo courtesy of Air Dog Website

3. Fuel Filter Housing O-Ring Leaks

One of the most common LB7 Duramax problems is leaking O-rings on the Fuel Filter Housing. As these trucks continue to get older, the original o-rings can deteriorate over time. They’re also susceptible to normal wear and tear. If you’re going to own an LB7 Duramax over an extended period of time, the odds are you will experience this problem.

A leaking o-ring not only results in a fuel leak, but air can also enter the fuel system. This causes various performance issues, hard starts, and even engine codes.

Fixing LB7 Duramax Fuel Filter Housing O-Ring Leaks

There are inexpensive kits to totally replace the o-rings found on the fuel filter housing unit. You can also replace the entire unit itself for more money. Take a look at some of the solutions we recommend below.

4. Water Pump Failures

Unlike the LBZ Duramax, the LB7 Duramax water pump is prone to leaking, not outright failure. The OEM water pump uses an iron impeller which makes it much more durable than the plastic impeller used on newer models. Instead, over time the seals can deteriorate resulting in lower coolant levels because of coolant loss. This can cause overheating issues. Leaks also reduce pressure, causing the coolant system to inadequately supply coolant.

Replacing the LB7 Water Pump

Replacing the water pump on an LB7 Duramax isn’t as easy as you would think. Because of its location, you have to remove a few different components to get the pump off. To fix a broken or leaking water pump, you just have to replace it. We recommend using a quality OEM water pump when you replace your broken one. Depending on your truck’s mileage, you should also consider replacing nearby parts like the water pump housing, or even the thermostat. Take a look at what we recommend below.

LB7 Duramax Water Pump

GM 19168888

5. Overheating

Overheating issues are more common on LB7 and LLY Duramax trucks than future generations. This is most likely because they have a smaller radiator and fan than 2006 or newer models. Overheating issues typically occur because of a faulty water pump, or a damaged fan clutch. When the fan clutch is damaged, it prevents it from operating and giving the LB7 Duramax engine the additional cooling it needs.

Overheating can also be attributed to a dirty or clogged radiator. Over time, your radiator can accumulate dirt, grime, and other gunk. To make things worse, the factory radiator is a little small. This means a smaller surface area and even less overall cooling capacity.

How to Fix LB7 Duramax Overheating

First, you want to identify what is causing overheating on your LB7 Duramax. You can definitely start by making sure your radiator is free and clear or debris, dirt or other gunk. Check for a bad thermostat or water pump. Try to find out under what conditions the overheating occurs. If your truck is only overheating under extremely heavy loads, that is generally more normal. If your truck is overheating anytime you drive it, you definitely have a problem that needs to be taken care of as soon as possible.

Once you’ve identified what the problem is, you’ll probably have to order some parts. Here are the parts we would use to fix our own LB7 Duramax. There are also some aftermarket solutions that can help, like Mishimoto’s LB7 performance aluminum radiator.

Mishimoto LB7 Performance Radiator

Performance Radiators like this one from Mishimoto often produce better cooling than factory units. Check it out here.

6. Head Gasket Failure

The LB7 Duramax is more prone to head gasket failures than future generations of the Duramax engine. Despite this, head gasket failure usually doesn’t occur until over 100,000 miles, so it’s not nearly as common as it is in 6.0L Powerstroke engines. LB7 Duramax head gasket problems can occur for a couple of reasons. Overheating can sometimes be attributed to head gasket failure, as the LB7 Duramax does suffer from a small radiator, fan, and problematic water pumps. Head gasket failure can also be attributed to performance modifications like tuning that allow the head bolts to stretch and a lifted cylinder head.

These aren’t the cause of all head gasket failures though. More LB7 head gasket failures are attributed to the poorly designed head gasket found on these trucks. The LB7 Duramax has a layered steel head gasket. During the compression stroke, the head can lift a little. This in turn, can result in gaps in the steel head gasket. The layered gasket will then leak. Leaks can occur internally or externally. Internal leaks result in coolant reaching the cylinders, while external leaks result in coolant loss.

How to Fix A Blown LB7 Duramax Head Gasket

Once you’ve determined that the head gasket on your LB7 Duramax is blown, you’re going to want to fix this problem asap. Unfortunately, this can be pretty complex and require a skilled mechanic. Even for a skilled mechanic it takes over 10 hours to do everything right.

While we recommend OEM parts a lot for maintenance, and even some repairs, it’s best to go with Aftermarket parts when replacing your head gaskets and head studs. ARP head studs are second to none and provide vastly better clamping force than the stock head bolts. GM has since updated their head gaskets to be more durable, so it is possible to use a new OEM gasket. Merchant Automotive makes a complete head gasket kit that is of better quality. If you want to make your LB7 Duramax more durable than the factory design, this is the route you should go.

ARP Head Stud 230-4201

The ARP Head Stud Kit 230-4201 should be used when doing an LB7 Duramax head gasket job. These studs offer the best clamping force and drastically better performance than comparable studs from other manufacturers.

7. Allison Transmission

The Allison Transmission is well-known by diesel enthusiasts for being one of the most reliable transmissions ever. There is a reason GM has stuck with this transmission and continues to use them, even in today’s L5P Duramax. The original Allison wasn’t nearly as stout or beefy as more recent ones. In fact, when you tune your LB7 Duramax or add other performance modifications, the Allison 1000 transmission can enter limp mode. This occurs so often that we included it in our list of the most common LB7 Duramax problems.

The Allison 1000 transmission’s Limp mode feature is a fail safe to prevent further transmission damage from occurring. When it detects the transmission slipping, it’ll go into limp mode, seriously decreasing power. If you have a stock truck, you probably won’t have issues with your Allison transmission going into limp mode.

How To Fix A Limp Allison 1000 Transmission

With a stock truck, you probably won’t experience your Allison 1000 going into limp mode unless it’s time for a transmission rebuild. If it occurs, try cycling your key and turning the truck off and on. Sometimes you can reset the truck from limp mode. If you have a scan tool, you can simply clear the code which will release your LB7 from limp mode. A monitor like the Edge CTS3 Insight will also work to clear codes. If the issue continues to occur on a stock truck, your transmission will likely need a rebuild in the near future. For modified trucks, you can try the ATS Co-Pilot transmission controller.

8. LB7 Duramax Steering/Suspension Problems

The independent front suspension found on Duramax trucks is both a blessing and a curse. It gives a smoother ride, but it’s not quite as durable as the straight axle found on a Powerstroke or Cummins truck. It might do okay on a stock truck, but if you’re planning on bigger tires, wheels, or a lift kit upgrading the suspension and steering components is definitely recommended. These upgrades can also benefit you if you’re going to be towing heavy or if you are going to do any kind of off-roading.

What steering and suspension parts cause the 6.6L LB7 Duramax the most problems though? Broken or snapped tie rods are the most common issue. They’re often caused by other underlying issues however, like a worn or damaged pitman arm or idler arm. If you install a leveling kit, or simply torque your torsion bars, your factory steering geometry will be thrown out of whack too. This can lead to premature ball joint wear and control arm issues. For that reason upper control arm kits can be a lifesaver and can improve both the longevity of your factory parts and steering geometry.

Fixing your LB7 Duramax IFS Problem

Fortunately, the IFS system doesn’t have to permanently be a weak spot on your LB7 Duramax. With some aftermarket upgrades, you can greatly improve the steering and suspension on your LB7 Duramax. It’ll make it safer to drive while simultaneously improving steering response and overall front-end durability.

Tie Rods

Cognito Alloy HD Tie Rod Set

More durable than the factory Tie Rods, the Cognito Alloy Tie Rod set is beefier than the factory tie rods. In fact, when compared side-by-side the factory tie rods look tiny in comparison.

Kryptonite Death Grip Tie Rod Kit

Kryptonite Death Grip Tie Rods are a huge improvement over the factory tie rods. They’re more durable, and they offer a lifetime warranty.

Upper Control Arms

Kryptonite Upper Control Arm Kit

Kryptonite UCAs are a huge improvement over the factory control arms. If you’ve added a leveling kit to your LB7 Duramax or cranked the factory torsion bars, these are a MUST-HAVE.

Cognito Box-Style SM Series UCAS

Cognito SM series box style upper control arms help bring steering geometry back to normal levels and bring ride quality back to comfortable! A must have for leveled Duramax trucks.

Cognito Uni-Ball UCAs

For off-roading, Cognito’s Uni-Ball Upper control arm kit is the perfect solution. The uni-ball ball joint is much sturdier and can handle more abuse than the standard ball joint.

Pitman And Idler Arm Support Kits

Cognito Pitman And Idler Arm Support Kit (PISK)

The Cognito pitman and idler support arm kit adds additional support to critical LB7 Duramax steering components. Basically, the forward and rear movement of the center-link is eliminated.

Kryptonite Pitman and Idler Arm Support Kit

Another VERY similar PISK kit for improved steering reliability. The Kryptonite Pitman and Idler Arm Support kit offers the same benefits as the Cognito kit.

Other Steering/Suspension Upgrades to Consider

Parts	Part # & Link to Buy
Pitman Arms Moog Kryptonite OEM	See Below MOOG K6654HD Kryptonite KR6654 GM 19168473
Idler Arm Moog Kryptonite OEM	See Below MOOG K6535HD Kryptonite 10KDG535 GM 19153392

Front End Packages

9. High Horsepower LB7 Duramax Problems

Other LB7 Duramax problems occur almost exclusively with high horsepower applications. If you’re vehicle is mostly stock, these aren’t problems you need to worry about. If you are building a high performance truck however, these are things you need to consider. It might be better to keep your truck in more stock form, therefore making it more reliable. If you decide to pursue higher horsepower and torque, these are some problems you need to be aware of.

Snapped Crankshaft

High horsepower Duramax trucks of all generations are susceptible to snapping a crankshaft. Excessively high RPMs and poor tuning have attributed to some crankshaft failures. Some people also blame the firing order for putting additional stress on the crankshaft. Breaks typically occur near the number one and two rod journals.

Fixing a broken crankshaft is an expensive repair that can result in your truck being in the shop for weeks or months. There are several aftermarket crankshafts that hold up to power better than the factory unit. Do your research before buying and make sure you’re working with a reliable shop that knows what they’re doing. You only want to have to tear down your motor once.

Bent Rods

Another high horsepower LB7 Duramax problem is bent rods. The factory rods are forged steel, so they’re not necessarily delicate, but they are the weak point in the LB7 Duramax Diesel engine. The LB7 Duramax engine has a 17.5:1 compression ratio, and this, along with the excessive torque present when adding performance modifications places extra stress on the engine’s internals. Instead of breaking and an all-out rebuild being needed, the forged steel rods simply bend.

Learn More About the LB7 Duramax

You can learn more about the LB7 Duramax by visiting some of our other resources. Click on one of the links below to visit that LB7 Resource.

• LB7 Duramax Specs
• Comprehensive 6.6L LB7 Duramax Maintenance Guide