Fuel Pressure

Keith Browning · August 30, 2005

What is the correct fuel pressure spec for a 2005 C7 CAT engine? That would be at the filter head, correct?

HeuiTim · September 1, 2005

Dont know what C7 your working on but here is the spec for the C7 KAL S/n.

Fuel System Pressure - Test

Low Fuel Pressure

Low fuel pressure can cause low engine power. Low fuel pressure can also cause cavitation of the fuel which can damage the fuel injectors. The following conditions can cause low fuel pressure:

Plugged fuel filters

Debris in the check valves for the fuel priming pump (if equipped)

Sticking or worn fuel pressure regulating valve in the fuel transfer pump

Severe wear on return fuel pressure regulating valve at the rear of the cylinder head

Worn gears in the fuel transfer pump

Pinched fuel lines or undersized fuel lines

Old fuel lines that have a reduced interior diameter that was caused by swelling

Fuel lines with deteriorating interior surfaces

Pinched fuel line fittings or undersized fuel line fittings

Debris in the fuel tank, fuel lines, or fuel system components that create restrictions

High Fuel Pressure

Excessive fuel pressure can cause fuel filter gaskets to rupture. The following conditions can cause high fuel pressure:

Plugged orifices in the fuel pressure regulating valve

Stuck fuel pressure relief valve in the fuel transfer pump

Restricted fuel return line

During normal operating conditions and load conditions, the fuel system should maintain the following pressure:

400 to 525 kPa (58 to 76 psi)

At low idle, the fuel system should maintain the following pressure:

400 to 435 kPa (58 to 63 psi)

The pressure differential is the difference between filtered fuel pressure and unfiltered fuel pressure.

With a new filter, the pressure differential across the fuel filter will be the following amount:

35 kPa (5 psi)

As abrasive particles collect in the fuel filter, the pressure differential across the filter will increase. When a filter becomes plugged, fuel supply pressure may drop as low as 69 kPa (10 psi) before a significant power loss is detected by the operator. Low fuel pressure will cause cavitation and internal damage to the unit injectors. The pressure differential across the fuel filter should not exceed 69 kPa (10 psi).

Pressure regulator (8) is mounted directly in the rear of the cylinder head. The regulator is located at the fuel return port toward the rear end of the fuel supply passage. The orifice maintains fuel pressure at low engine rpm. The regulator contains a check valve that prevents fuel from draining out of the cylinder head and back to the tank during engine shutdown.

In order to check the unfiltered fuel pressure (fuel transfer pump pressure), follow this procedure:

Install the pressure test group onto the engine.

For type I fuel systems that contain a fuel pressure tap (10) that is installed in the inlet port of the fuel filter base, remove the plug from the pressure tap. Install Tooling ( and Tooling © on the fuel pressure tap (10) .

Install Tooling (A) in order to measure the fuel pressure.

For type II fuel systems without a pressure tap, install a t-fitting in the fuel line for the unfiltered fuel pressure (10). If necessary, install Tooling ( and Tooling © on the t-fitting.

Install Tooling (A) in order to measure the fuel pressure.

Start the engine and record the unfiltered fuel pressure.

To check the filtered fuel pressure, follow these steps:

Remove the plug from fuel pressure tap (11) .

Note: Install Tooling (A) in order to measure the fuel pressure.

Start the engine and record the unfiltered fuel pressure.

Keith Browning · September 8, 2005

It turns out that the truck was spec'd out wrong /forums/images/%%GRAEMLIN_URL%%/eek.gif and CAT recommended upgrading the calibration for more horsepower and torque. The catch is that the trans specs will only allow this with a different gear ratio so it looks like I may be doing a gear swap in the rear end in the future.