What To Do To Help Prevent CP4 Failure On Your LML Duramax Diesel

What is the Issue With The CP4 Pump?

The High Pressure Fuel Injection Pump on the 2011-2016 LML Duramax Diesel is notorious for “grenading” and sending metal shards throughout the fuel system causing very high repair bills after. This is due to a design flaw in the Bosch CP4 injection pump, Bosch designed the unit for the quality standards of diesel fuel in the European Market, which has a higher lubricity than the Ultra Low Sulfur Diesel, ULSD, that we get here in the United States. The wear scar diameter of European Diesel Fuel is 460 Microns while the Ultra Low Sulfur Diesel in the US has a wear scar diameter of 510-520 Microns, this lack of lubricity leads to accelerated wear of the internal roller and cam. In addition to the lack of lubricity the cam and roller can be worn out from fuel contamination, fuel starvation or fuel temperature variations.

What Can You Do To Help Prevent CP4 Failure?

We recommend to run Opti-Lube XL Xtreme Lubricant Formula in your fuel to lower the wear scar rating and improve lubricity. When diluting Opti-Lube XL and ULSD 1:512 it reduces the wear scar diameter to 240 microns and if you want to reduce the dilution to 1:1280 it reduces the wear scar diameter to 370 microns. After adding Opti-Lube XL it greatly increases the lubricity of the ULSD and much surpasses the standard for European Diesel Fuel. This combats any issue that may come from lubricity but there still is the issue of fuel contamination, starvation and temperature variance. We recommend running a lift pump with filtration, we have seen the best results from the Airdog II 4-G. The lift pump will provide positive pressure from the fuel tank to the CP4 pump as well as providing additional filtration to keep any contaminants out of the fuel. On the LML Duramax platform GM removed the fuel cooler that was located in front of the tank on older models, this can lead to the fuel heating up and putting your fuel system in harm's way.

Can I Prevent CP4 Failure?

In short the answer is no, the only way to prevent a CP4 failure is to do a CP3 conversion, there are many different kits on the market. We prefer the S&S 50 State Legal kit because it does include everything needed to maintain the factory emissions equipment and it will pass smog. By replacing the unstable CP4 pump with a much more reliable CP3 pump that has been proven on many different Common Rail Diesel Platforms for 10+ years you will no longer have to worry about your injection pump grenading and sending metal shards through your fuel system. 






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