EPA 2010 and later DT, 9 & 10 engines use a fuel module that incorporates many features, including an electric fuel pump, fuel heater and fuel strainer.
-The fuel strainer can be seen when the pump is removed from the filter module. The strainer should be cleaned at the filter replacement interval (30K miles / 43K Km / or 12 months). The strainer P/N is 1899335C91 (see images below)
-Low fuel pressure and Hard Start or No Start conditions can be caused by at least two manufacturers of non OEM fuel filters. See differences in the fuel filter seals here and fuel filter recall G-Letter here.
-Navistar has received complaints that NAPA fuel filter FIL3994 can cause low fuel pressure. CARQUEST and WIX 86994 appear to be made by the same mfg. as the NAPA filter.
-Navistar's OEM fuel filter was developed specifically to work with features that are designed into the fuel filter housing. These features remove air from the fuel system and produce the required fuel pressure, giving the engine optimum performance.
-Calibration updates have been made due to low fuel pressure DTC's 94-1, 94-17 being set erroneously. Do not perform diagnostics for these faults unless there is a starting or performance complaints.
-Update the engine calibration (see calibration scorecard)
-If the vehicle has this code(s) and has a performance complaint then update the engine calibration AND follow step-based diagnostics (at the beginning of this article)
-Some low fuel pressure complaints are caused by a worn fuel pressure regulator valve & spring. Kit 1893801C94 is available to remedy this.
-Low fuel pressure complaints can be caused by the wrong O-ring being installed on the fuel pump
Fuel pressures above 60 psi will not cause low power or performance complaints on this engine
-Fuel inlet restriction should not exceed 8.14" Hg. / -4 psi. High inlet restriction can cause the pump to draw too much current and shut off or behave erratically (this could be caused by an intermittent fuel restriction in the fuel tank or anywhere in the line). Use ZTSE6009 adapter to attach a vacuum gauge to the fuel inlet.
ELECTRIC FUEL PUMP OVERVIEW
At key ON, the ECM closes the fuel pump relay (provides ground via pin C-76) and battery voltage is supplied to the pump. The pump will run for ten seconds (time varies with coolant temperature) and then shuts off. During the run time if the ECM does not detect crankshaft rotation it switches the fuel pump relay off. The key must be OFF for at least 10 seconds and then cycled ON before the ECM will restart the fuel pump.
DIAGNOSTIC TIPS:
The pump has internal overload protection that turns the pump off under overload (high current draw situations). High current draw can be caused by high inlet restriction or restriction in return line to tank. When current limiting protection is triggered, the pump will cycle on and off causing the system pressure to fluctuate until the overload condition is resolved. The pump may eventually turn itself off. This situation can occur without a fault code being set. When the ignition key is cycled OFF for 10+ seconds and ON the pump will restart'''
found that the fdp sensor on the new filter housing was yellow and the original one and new one I replaced old one with is blue, switched the yellow one out with the new blue one and it started reading 75psi. Road tested with the laptop hooked up and it maintained 75psi throughout the trip with no fuel filter dtc.
