LML Catastrophic Pump Failure

Common Problems

Published in the July 2019 Issue July 2019 Ask The Expert, Feature

If you’re driving a truck with a 2011-2016 Duramax LML diesel engine and haven’t yet experienced a major fuel pump failure, you’re likely living on borrowed time. If it hasn’t been fixed, it’s likely going to occur in the near future.

However, the crew at InjectorsDirect.com have tackled this problem and found what causes the failure and how it can be fixed. The editors of Diesel Tech Magazine contacted InjectorsDirect.com and have received the following information put together by Daniel Lehmkuhl which can be found on InjectorsDirect.com blog.

CP4 High Pressure Fuel Pump Failure

According to InjectorsDirect.com, the 2011-2016 Duramax suffers from a high pressure fuel pump issue unique to this year-range model. Failure of this CP4 pump is usually catastrophic, causing metal particulates to contaminate the entire fuel system.

If you own one of these particular trucks, it’s likely you’re well aware of the problem. If not, InjectorsDirect.com offers some basic reasons for this failure, how to diagnose a pump failure, and show you the parts you need to properly fix your vehicle.

Why Does it Fail?

The short answer: lack of lubricity. 

Lubricity is most commonly defined as the ability of a fluid to minimize the degree of friction between surfaces in relative motion under load conditions.

The CP4 injection pump creates higher pressures with less volume than its predecessor, the CP3 pump. Although this makes it a more efficient pump, the lack of volume creates a lack of lubrication since these pumps rely on the diesel fuel to act as a lubricant.

In addition to the higher pressure and lower volume, the removal of sulfur from modern diesel fuel (Diesel #2 or Ultra-Low Sulfur Diesel) also destroys compounds that exist in the fuel naturally that would normally contribute to increased lubricity. 

Some fuel resellers mix lubricity-increasing additives into their fuel prior to sale, but this is not consistent and not well-regulated. Using a commercially-available diesel fuel additive can be helpful, but cannot be guaranteed to prevent CP4 pump failure.

Diagnosing a Pump Failure

The LML and LGH CP4 pumps most commonly fail due to this lack of lubrication which causes internal metal parts (the drive cam, cam follower or pump piston, as well as the housing itself) to rub against each other and begin to shave off small metal particles.

These particles are immediately distributed throughout the fuel system causing catastrophic failure. Some pumps actually seize up completely and burst the aluminum housing open as a result of this failure.

Using lubricity additives doesn’t guarantee that your pump won’t fail someday, so it’s important to know what steps to take when it happens to you.

If you’re experiencing a hard start or no start, or are getting the following trouble codes; P0087, P0088, P0191, or P128E, a pump failure could be the problem.

Remove the CP4 pump and then the fuel pressure regulator for inspection. If the body casing of the pump is cracked, or you find metallic debris on the fuel pressure regulator screen, this is indicative of a pump failure.

Repairing Your Vehicle

GM mandates that you perform the following steps: First, replace the pump, rails, injectors, all high pressure fuel lines, return lines and fuel filter; second, clean and flush all fuel chassis lines, filter pipes and other engine mounted fuel system pipes (low pressure); and third, remove and clean/flush the fuel tank and fuel sender.

InjectorsDirect.com has put together complete repair solution for LML/LGH CP4 Pump failure using all OEM parts.

Simply flushing the fuel system is inadequate and could lead to residual contaminants in your fuel system. Contamination is the number one cause of repeat injector failure. Replacing all of the fuel system components is the only way to prevent recurring contamination issues.

InjectorsDirect.com offers this kit in a few different convenient configurations to meet your needs. The complete kit includes: Bosch OEM New LML Injectors (8), Bosch OEM New CP4 Pump (updated), Bosch OEM New Fuel Rails (2), Bosch OEM New Return Line Assembly, and GM OEM New High Pressure Fuel Lines (pump to rail, rail to rail and rails to injectors).

The full kit retails for $3,499.99. The kit without the pump retails for $2,899.99. The kit without the injectors retails for $1,549.99. For more information contact www.injectorsdirect.com.





1--LML Duramax CP4 pump housing damage after catastrophic failure.

2--Internal inspection of a failed LML CP4 pump reveals significant contamination.

3--Removing the fuel pressure regulator from a failed LML CP4 pump reveals significant contamination.

4--InjectorsDirect.com has put together a complete kit using updated Bosch components to properly repair LML & LGH fuel systems.


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