Normal and abnormal fuel system pressures are listed in the following tables. The pressures can vary slightly due to different chassis fuel line configurations, fuel temperatures, fuel filter condition, and fuel viscosity.

Normal Fuel System Pressures
Port Engine 600 RPM Engine 1800 RPM
LPP Inlet (in Hg) -4 to -8 -11 to -14
LPP Outlet (PSI) 72 to 80 100 to 126
HPP Inlet (PSI) 69 to 77 92 to 112
HPP Outlet (PSI) 1 to 2.5 4 to 7
Priming Port (PSI) 72 to 80 100 to 120
Fuel Compensation pressure w/ doser regulator 75 to 85 80 to 95

If the LPPI is greater than the specified range, check for inlet restrictions.

If the high pressure pump Inlet pressure is lower than the acceptable pressure, check the pressure difference across the low pressure pump outlet pressure sensor and fuel compensation pressure sensor. If engine does not have a low pressure pump outlet pressure sensor, install J-48876 and use priming port pressure.

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