So you just bought a LML Duramax, and you're curious if it has been CP3 Swapped, how can you tell?

You just bought a 2011-2016 LML Duramax and you aren't sure what the previous owner/s did as far as modifications. You commonly see posts in forums about CP3 Conversions and you are wondering if your truck has been swapped. How can you tell? This is what we will be discussing here.


From Model Year 2011 thru 2016, General Motors used a High Pressure Fuel Injection Pump from Bosch, dubbed the CP4.2. This injection pump is capable of some extreme peak pressures (30KPSI!). A common misconception in terms of the CP4, is that the ".2" designates an updated model of sorts, which is not the case. The ".2" refers to the use of two high-pressure cylinders, which are seen on each side of the pump. (There is a CP4.1, which is a single cylinder version commonly used in smaller diesel cars.)

Interested in the differences in a CP3 vs CP4.2? Our friends at S&S Diesel Motorsports put together this video comparison. 

You came here to figure out where to look on your truck, lets dive into the valley.

 We will start by taking a look in this area here.


Looking more closely, we will see if we can locate the FCA on the CP4.2, which has a yellow and black wire running to it, shown here. 

Closer look at what we are after.

 If your connector is horizontal like the images above, you have a CP4.2. If it was to be vertical with the wires at the top, that would be a CP3.


Still are not sure which you have?

Lets take a look at the passenger side fuel rail. Because the CP4.2 has 2 High Pressure Fuel lines, and a CP3 only has one, we can look here to tell as well. 

Shown here, all ports on the rail are accompanied by a line, this means the truck has a CP4.2.

Shown below, you'll notice a cap and plug on the 3rd Port from the front, this means the truck has been CP3 Swapped.

Below, you can see 2 High Pressure lines running of the Injection pump, which as covered earlier, tells us it is a CP4.2.

Below, is a S&S 50 State Legal CP3 Conversion Kit, which shows the 1 High Pressure Line. 


You've reached the end of this blog post, and I hope you have been able to confidently identify the High Pressure Injection Pump on your LML Duramax and perhaps better your knowledge on the differences thanks to our friends at S&S Diesel Motorsport's video.

Thanks for reading!


 Photo credits

John C Garage

Aaron Smith


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