FYI- There is a cp4 tread in the gen 5 heavy duty section discussing the issues with the cp4.
A partial excerpt from a class action lawsuit explaining the problem with the cp4 pump:"The primary reason the cp4 pump is said to fail is because the pump was not designed for diesel fuel in the USA.
Bosh is a euro co and uses euro diesel fuel with more sulfur than the us diesel fuel. The cleaner ultra-low sulfur diesel used in the us does not lubricate the cp4 as well as the euro diesel, makes it difficult on the cp4`s hydraulic pistons to continue working, according to experts at Diesel Army.
The cp4 is said to struggle to supply adequate fuel to the engine under lower pressure of these more efficient engines. The result is the formation of air bubbles inside the cp4 . Air in the pump means that metal rubs against metal, causing accelerated wear.
This will eventually cause the cp4 to fail, often around 100k mi. Before it fails, metal shavings are produced which travel into the fuel injectors and fuel lines with catastrophic results."
Unquote: Some owners have resorted to expensive "fixes" to counter the problem, such as, fuel additives, booster pumps and or re-routing lines w/filters back to the fuel tank, or replacing the pump with a cp3 model to name just a few!
So far, not much "long term data" on the success of diesel additives solving the cp4 issues, BUT, the tests that are available are promising!
IMO, If I had a cp4, after a lot of research, I would certainly use a top tier additive in hopes that it would save my cp4 pump!
In the end, there is lots of info out there, it`s up to individual to choose what`s best for them!