Odds are if you’re an LML owner you’ve heard of the dreaded CP4 failure. It is a somewhat common occurrence, and many people are unsure of what it is and how it works, so we will give you a brief explanation.

Let’s start off with the basics, and some commonly asked questions such as, “What is an injection pump? What are the components of a fuel system? Why does CP4 failure require a full fuel system replacement and not just a new pump?” Let’s dive in- modern diesels require fuel to be pressurized up to 27,000 PSI in order to properly function. Your injection pump draws fuel from the tank, or if a lift pump is installed, it is fed fuel by the lift pump, and then pressurizes it, once pressurized, your fuel is fed through your main pressure line to your fuel rail, which then distributes fuel evenly to your injectors. Now that we have that covered, let’s dive into the CP4 specifically. GM debuted the CP4 in 2011, ditching the popularly loved CP3 which offered hundreds of thousands of trouble-free miles from 2001-2010. Shortly after the CP4’s release, it began showing its true colors, destroying fuel systems in matters of seconds. When the CP4 fails, it releases metal shavings, which quickly plug up injectors, fuel lines, and rails, and even sometimes find their way into the return line and into your fuel tank. This makes for a long, expensive, teadious repair. If your CP4 fails, you must replace fuel rails, lines, and injectors. Along with this, it’s not uncommon to have to drop your fuel tank and ensure it is clean and free of shavings along with your feed and return lines.

We offer a cheaper, and easier fix to this. We offer CP3 conversions you can do before your CP4 fails, so you are only required to change the pump, which is easier on your wallet. We offer a wide range of CP3 conversions to fit your specific needs, including power goals and emission compliances.

Are you now scratching your head wondering which CP3 conversion is best for you? Here is a great read by Under-Dog Diesel to help you decide!