Everything You Need To Know About Diesel Fuel Pumps

Given the tremendous fuel pressure associated with diesel fuel pumps, they can be a complex subject – shrouded in mystery, but sometimes the Achilles heal of certain Power Stroke engines in particular. Thankfully S&S Diesel Motorsport does a really great job of breaking it all down for us – from operation, sizing, and important distinctions between models used in these powerful diesel engines.

What Fuel Pumps Do Factory 6.7L Power Stroke Engines Use?

Ford’s 6.7-liter Power Stroke diesel engines are well-regarded for their power potential, a capability that hinges on a specific component: the high-pressure fuel pump. These engines use a pump known in the industry as the CP4, a key part of the common-rail fuel injection system.

The job of this component is to generate the high pressure needed to deliver fuel to the injectors. Ford used different versions of these pumps over time.

S&S explaining the basics behind fuel pumps

Ford trucks that were manufactured between 2011 and 2014 had one design, while those built from 2015 through 2019 came with a modified version featuring a longer internal stroke.

After some time, Ford decided to switch from the CP4 pump entirely in 2020, opting for a different pump design for the 6.7-liter Power Stroke.

What Size Are the Fuel Pumps in These Trucks?

Bosch, the manufacturer of these pumps, uses a particular designation to identify the size of the pumps. The earlier 6.7-liter Power Stroke engines, those from 2011 to 2014, used a CP4 known as an “r90.”

The “90” refers to a displacement of about 900 cubic millimeters per revolution. Another defining feature of this pump is its 6.75-millimeter stroke.

Between 2015 and 2019, Ford used a revised CP4, called an “r99,” which had a displacement of up to around 995 cubic millimeters per revolution. This was mainly accomplished with a longer, 7.5-millimeter stroke. It is worth noting that the stroke length plays a role in the pump’s capacity.

How Do They Function?

These fuel pumps are sophisticated pieces of equipment, using internal plungers driven by a camshaft. The specially shaped cam forces each plunger to cycle twice per revolution, which compresses the fuel.

A component called the inlet valve also plays a major role in this activity. “The actual flow of the pump depends on other things like supply pressure, RPM, IMV or FCA milliamps, and rail pressure,” Luke from S&S explained.

This valve accurately controls the amount of fuel going into the pumping chambers, thus regulating the output flow.

How Are They Sized?

The key to understanding fuel pump sizing is the concept of displacement. According to Luke, “This is the simplest way to size pumps; that’s the way that Bosch sizes pumps.” Displacement measures volume.

It indicates the amount of fuel a pump can move in a single revolution, expressed in cubic millimeters per revolution. Elements such as the internal plungers’ bore (diameter) and stroke are factored in to calculate this number.

The “r90” version of the CP4, for example, has a 6.5-millimeter bore and a 6.75-millimeter stroke. It produces a displacement close to 900 cubic millimeters per revolution.

The “r99” model used on later engines has a longer 7.5-millimeter stroke, which increases the displacement to around 995 cubic millimeters per revolution.

 

What else would you like to know about diesel fuel pumps? We’d love to hear from you. Email: [email protected].

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