12/22/2025
We have a new "that's not a stupid question" for you today!
Q: With CP4 pumps being a common trouble spot, do fuel additives offer any help?
A: The experts at AMSOIL INC. weighed in: It’s no secret in the light-duty diesel world, that many folks are seeing issues with their CP4 pumps. These struggles seem to stem from a design perspective and potentially from the fuel that we’re running through it. While it’s not an ironclad solution that will solve all CP4 pump issues, running fuel additives will definitely prolong the life of your CP4.
Unfortunately, there’s not much science to prove that if you simply additize your fuel, you won’t have a CP4 pump failure. But, when you know you have a pump that struggles to begin with, adding lubricity to your fuel will never hurt that pump. In fact, it may prolong the life of that pump.
Lubricity additives were invented for fuels to protect the fuel pump and the injectors because of the way ultra-low sulfur diesel is processed and made. Lubricity is added back to the fuel because its stripped out when ultra-low sulfur diesel is made.
The more lubricity you can put in that fuel, the better your fuel system will operate. That lubricity provides a cushion between anything in that system.
In the fuel pump itself, as it’s spinning fuel, the lubricity agent will help that fuel pump, as well as the needle inside the injector and protects it from wearing out.
Again, nothing is a guarantee, but using a lubricity additive means you’re doing the right thing by giving the fuel system the best opportunity to perform well.
Now, alternatively, many aftermarket companies are saying you could remove your CP4 and go back to a CP3, and some are rebuilding the CP4 and claiming it’s a better product. Either way, the better scenario for any of those components to live a long life is through the use of fuel additives as well.
The condition of your particular CP4 pump will depend on how you’re running your truck, what loads the engine is under, what fuel you’re using, and how many miles are on it.
AMSOIL has a few additives that can help protect your CP4 pump, such as an All-in-One that has lubricity, detergent, cetane, and cold flow improver. There’s also a diesel injector clean plus cetane boost, and one without the cetane.
When it comes to making sure your CP4 pump doesn’t gr***de, using a simple fuel additive in every tank of diesel, is well worth the protection you’re giving your truck!
