Fuel System
NOTE:
The following step numbers refer to the numbers in the accompanying flow chart(s).
- Install Fuel Pressure Gauge (J-25400-300) at fuel line service fitting. Measure fuel pressure while cranking engine. If fuel pressure is 9-12 PSI, refer to performance diagnosis CHART A5 - INJECTOR SYSTEM DIAGNOSIS.NOTE: The DFI system requires that fuel pressure be 9-12 PSI and steady under all driving conditions. The fuel pressure gauge may not show small variation in fuel pressure. For a more precise and responsive reading, use the 0-15 PSI gauge head from the Essential Tool Gauge (J29658/BT8205) attached to the hose with Schrader valve fitting from the Essential Tool Gauge (J34730-1).
- If fuel pump relay or ECM were the cause of low fuel pressure, there would be an ECM code E20 set. This step is to check for voltage supply to fuel tank 4-way connector.
- If voltage signal to fuel tank connector is okay, an open may exist between the 4-way connector and the fuel pump. If fuel pump runs with an alternative power source connected, fuel tank unit is okay. Check throttle body fuel metering assembly for cause of low pressure.
- Check fuel supply system (tank, filter, pump, sender, supply line) for ability to deliver 9 PSI, or check for faulty throttle body fuel pressure regulator.
- If pressure is low with fuel return line plugged, throttle body fuel metering assembly is not at fault. A restriction or blockage may exist in fuel supply system. The fuel supply line should be checked visually. The fuel filter element can also restrict flow. Check for proper fuel line routing. Check sender tubes for restrictions. Check for leaks or restrictions between rubber coupler, pump and sender. Check for collapsed, mispositioned or restricted fuel strainer in tank. If all of the above are okay, replace fuel pump.
- Fuel pressure above 12 PSI is caused either by a malfunction of the pressure regulator or by a restriction in fuel return line. It should be noted that a secondary condition of spark plug fouling (code E45 or oxygen sensor contamination resulting in code E13 accompanied by E45) may result from too rich fuel flow. To isolate cause of high fuel pressure, disconnect return line at throttle body and connect a suitable fitting to throttle body which will accept a length of flexible rubber fuel hose. Insert other end of hose into a suitable fuel container and observe fuel pressure as ignition switch is turned on. If the fuel pressure remains above 12 PSI, replace fuel meter assembly. If fuel pressure drops to correct pressure range of 9-12 PSI (with fuel return lined by-passed), fuel return line is restricted. A restricted fuel return line can be diagnosed by visually inspecting the line. A kink in the Teflon fuel line (braided stainless steel clad) may not be visually obvious.
- If fuel pump will not run with externally applied power, fault is either an electrical opening in fuel sensor unit wiring to pump, an open at the RFI suppression connector inside tank on pump or a faulty fuel pump. The fuel sending unit must be removed from vehicle to be checked.