Duramax LML CP4 Pump Failure

Previously on older models, there wasn’t much of an issue with the fuel system, but with the newer models there was a design change introduced as a cost reduction to the LML platform, (since a smaller amount of fuel is required when running the more efficient piezoelectric injectors). Even if you have a 100% stock truck your pump is still a ticking time bomb.

The new CP4 injection pump creates higher pressures with less volume meaning a more efficient pump, but with the lack of volume is a lack of lubrication, therefore creating these failures. In Europe the CP4 has been used for years with very little trouble, reason being is their fuel has more lubricity than our country's Ultra low sulfur diesel fuel (ULSD), and does not even come close to meeting the minimum spec for lubrication to keep highly stressed components like those hydraulic pistons in the pump lubricated.

You accelerate wear any time you fill up with ULSD. There is an assortment of additives on the market, like, FPPF Total Power, that aid in lubricating our poor quality fuel we have to use, and while it does help; it does not solve the entire problem with the CP4s lack of fuel in modern diesels, which creates more power than these pumps can handle, without some help from the aftermarket.

Another important part of the fuel system is the filtration. With aftermarket lift pumps (Duramax's do not have lift pumps, just injection pumps), from companies like Fass or Airdog, they have built in fuel filters and water separators, so you can rest assured you are providing positive clean fuel pressure to your injection pump, (keeping the pump from having to pull a vacuum from the fuel tank, which will greatly reduce the stress on the injection pump). A lift pump is something we highly recommend on any diesel that comes through the shop tuned or not. A lift pump will help extend the life of your truck, and the extra filtration will pull out the contaminates and water in the fuel.

Lift pumps come in specific kits to fit your application and typically are a fairly straight forward install if you’re a DIY’er, kits range from $600-800 for most applications. All of these parts are listed on our website for purchase and delivery. See FASS or AirDog fuel systems. Or call the shop for installation, or come in for any orders. We offer full installation of all the parts talked about and much more for your diesel truck.