How does a CP3 swap affect my MPG and towing fuel economy?

[HeavyHaulHabit]

Does the CP3 pump use more energy to turn than the CP4? What kind of changes in MPG are you guys seeing after the swap? How does it perform under heavy load—does the engine feel more or less efficient?

 

[BadlandsBuilt]

You might lose about 0.5 to 1 MPG because the CP3 is a larger, more robust pump that takes a bit more parasitic load to drive. What you gain, however, is a much more stable fuel rail pressure under load. How it feels when towing: the truck feels much more consistent on long hills because the CP3 isn't struggling to keep up with the injector demand like the CP4 sometimes does. To me, the tiny hit in MPG is worth the massive gain in reliability.

 

[CopperAndChrome]

Under heavy load, you won’t feel a loss in efficiency, but you’ll definitely feel a gain in consistency. The CP3 has a legendary track record for holding rock-solid rail pressure even when you’re pushing it up a steep grade with 15k lbs behind you. I’ve towed through the Rockies since my Y78 swap, and my towing MPG stayed at a steady 10.5—exactly what I got with the CP4. The engine doesn't feel "heavier" or less efficient; it actually feels a bit smoother because the CP3 provides a more stable fuel delivery than the high-strung CP4.