Series 40E Troubleshooting – Section 11.11 Fuel Pressure Full Load

Section 11.11
Fuel Pressure Full Load

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Figure 1. Diagnostic Form

The Fuel Pressure Full Load Test, ICP Pressure Test and Boost Pressure Test may be performed simultaneously at full load conditions. Refer to “11.12 Icp Pressure”

. Refer to “11.13.2 Test Procedure”

. Follow this procedure for the Fuel Pressure Full Load test. For a reproduction of the applicable portion of the diagnostic form, see Figure .
“Diagnostic Form”

. ‪

Section 11.11.1

The purpose of this test is to determine if the fuel system is supplying the engine with the proper fuel quantity and pressure at full load conditions.‪

Section 11.11.2
Test Procedure

If the fuel filter is equipped with a water-in-fuel probe, check with the vehicle operator to determine if the water-in-fuel lamp has been illuminated during vehicle operation. Then proceed with the following test procedure.‪

  1. If the pressure gage was not connected to the fuel system in Test 2, Sufficient Fuel/Pressure Test, remove the air bleed valve on the fuel filter header. See Figure
    “Fuel Pressure Tap Location”


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    Figure 2. Fuel Pressure Tap Location

  2. Install a 1/8 in. (3 mm) pipe fitting in place of the bleed valve.
  3. Connect a line from the fitting to the 0–160 lb/in.2
    (psi), gage of the Pressure Test Kit. Start the engine and run at low idle to check for fuel leaks in the line to the pressure gage. See Figure
    “Measuring Fuel Pressure with Pressure Test Kit”


    Note: Bleed the air from the fuel line to ensure an accurate reading.

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    Figure 3. Measuring Fuel Pressure with Pressure Test Kit

  4. Drive the vehicle on the road until the engine reaches operating temperature. Find an open section of the road and select a suitable gear. Depress the accelerator pedal (full depression) to the floor and accelerate to rated speed and 100% load.

    Note: Driving the vehicle uphill or fully loaded will facilitate efforts of reaching the proper engine loading at the rated engine speed.

  5. Measure fuel pressure and record on the diagnostic form. If pressure is not within specifications, replace the fuel filter, clean the fuel strainer and check fuel pressure again.

    Note: It may take a number of crank cycles to purge the air out of the fuel system after replacing the fuel filter.

If the fuel pressure remains low after replacing the filter, perform the Transfer Pump Restriction Test. Refer to “11.3.2 Test Procedure”


Section 11.11.3
Possible Causes

The following conditions are possible causes of fuel pressure problems:‪

  • A fuel filter or clogged fuel strainer could cause high restriction and low fuel pressure because of dirt or fuel jelling in cold ambient temperatures. Replace the fuel filter; clean the strainer and test again.
  • Debris in the fuel regulator valve will cause low fuel pressure. Refer to “11.3.2 Test Procedure”


  • A kinked or severely bent fuel supply line or blockage at the pickup tube could cause restriction and, therefore, low fuel pressure. Refer to “11.3.2 Test Procedure”


  • A loose fuel line on the suction side of the fuel system could cause air to be ingested into the system and cause low fuel pressure. Refer to “11.3.2 Test Procedure”


  • The fuel pump could have internal damage, e.g. seized plunger or leaking check valves.

Section 11.11.4
Tools Required

Engine Field Test Kit, J 39257
, and appropriate line with 1/8 in. NPT fitting.‪

Series 40E Troubleshooting Manual – 6SE241
Generated on 10-13-2008