LB7 Duramax Problems and Their Solutions

LB 7 Duramax Problems

If your heart's set on buying an LB7 Duramax pickup truck or you currently own one, then you must take note of the most common LB7 Duramax problems. We have compiled common problems to the most uncommon to help pickup truck buyers and owners make a sound decision. This is a list of LB7 Duramax problems and their solutions.


Garage owners, truck technicians, and repair specialists have a lot to say about the Duramax LB7. Many say that the 6.6L Duramax has a powerful engine. This V8 diesel from GM can give you thousands of miles of awesome use, but can be prone to the following problems:

Broken crankshaft

One of the most outrageous LB7Duramax common problems is a broken crankshaft. This means that you desperately need to take your car to a repair shop because it won't run at all. In most cases, your car will be at the shop for weeks or months as this part has to be ordered, delivered, and installed by a capable technician. It's also easy to see that this is not a cheap repair as you may need to spend hundreds of dollars to order a new factory crankshaft.

A weak crankshaft is common in powerful Duramax models, but it can also happen in other Duramax versions like the LB7, LML, LMM, and the LLY. The crankshaft break usually happens along with the first rod journal, and experts say that it's due to increased RPM as well as a very heavy external counterweight. Some reports also point that a firing order that affects the front section of the crankshaft may be causing the stress. 

To solve this, technicians replace the broken crankshaft with a well-balanced billet model, just like an internally-balanced Callies crankshaft that’s created from a very durable multiple-treated 4330V steel and also comes with lowered rod journal sizes. 

Also, preventing fatigue of the component located at the crankshaft front is essential. Using alternate fire camshafts with a new firing order, the vulnerable part is removed, and the overall weight is more equally distributed all over the crankshaft. 

CP4 problems

Problems with the CP4 is particular with the LML code that Duramax created from ’11 to ’16. These made use of the Bosch CP4.2 a high-pressure component fuel pump. Compared to the very durable CP3, the CP4.2 is not as reliable.

When water, debris or rust appears on the CP4.2 due to poor maintenance, this component can easily come apart. Also, the bucket that relies on the CP4.2 shaft may fail due to poor lubrication or the presence of dirt that affects the operation of the component.

When there are problems with the CP4.2, very harmful metal dirt may travel through the engine's fuel hoses, the fuel tank, and the fuel injectors. And as you can see, this is not just an expensive repair, but it's also very hard to do.

Also, GM’s warranty does not include contamination from dirt and water, and thus, it’s likely you’ll be paying for all the repairs. And you may avoid problems with the CP4.2 by using a lift pump or by swapping the CP4.2 with a CP3. The CP3 rarely has issues, even as your engine runs thousands of miles. Also, the CP3 can provide up to 20% more fuel volume and thus can improve the performance of your vehicle. 

Bent metal rods

Problems with the connecting rods are usually seen in engines with higher horsepower. Torque is the main reason for shrinking rods as high amounts of lo RPM pressure may be present when you have reached or the designated horsepower and torque.

This pressure is distributed on the crankshaft and piston, but the LB7 and LLY rods are the weakest components. These rods are made of forged steel, and thus these will bend before they break. You may not need to replace the entire engine block when this problem arises.

To solve this problem, you can replace the weak rods with affordable aftermarket rods. These rods are stronger and better with standards ARP2000 rod bolts at 7/16 inches.  

Cracking on the pistons

Another very common problem with LB7 Duramax is the presence of poor-quality piston castings. This is a problem with suppliers as there is a very noticeable reduction in metal along with the wrist pin. The crack on the piston is easily seen as it usually forms at the wrist pin's center line. The only way to solve this is to upgrade to aftermarket options.  

Injectors leaking

LB7 Duramax injector problems are also common with internal cracking of the body and the rusting of the inner ball seat. Later Duramax models use a hardened ball seat while the LB7 is equipped with a non-hardened seat. It will only be a matter of time when this ball seat starts to erode and will never be able to work properly.

A leaking injector will cause your truck to haze when it’s on idle, and there will be higher injector balance readings. This may be determined by a technician using proper diagnostic equipment.

The only solution is to replace the injectors, rather than experiencing problems for every component. Choose a good quality, new Bosch injectors as these come with a more durable body, hardened ball seats. Using these quality injectors will guarantee against cracking, leaks, and overall early failure.

Water pump issues

Leaking water pumps are also very common in a Duramax LB7. If you overlook leaks in the water pump, water can move to the underside, and this may cause more problems. Also, it’s very hard to pull and remove the water pump, and this may only be done successfully by a professional technician.


Now that you have a good idea about LB7 Duramax problems and their solutions, it would be best to consider these before you settle with this Duramax truck model. Most of these problems have very costly solutions as you need to replace the parts and components of the LB7. If you are not very keen on dealing with these problems, then you may be better off with a better type of truck rather than deal with these problems one by one.

About the Author JamesL Davis

James is a certified auto technician specializing in commercial vehicles. With 30 years of experience under his belt, James has encountered almost every type of automotive issue there is! Besides his day job at the repair shop, he is also an amateur race car driver.

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