Recommended Procedure:

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Remove the fuel line to the inlet side of the fuel pump. Install Fuel Pump Adapter 310-111 or equivalent between the fuel inlet line and the electric fuel pump. Connect test adapter to a 0-30 in-Hg vacuum gauge. Measure restriction at WOT (maximum engine speed out of gear with the brakes set and the wheels blocked).

If restriction is greater than 6 in-Hg, there is a restriction between the fuel pump and the fuel tank.

If restriction is less than 6 in-Hg but more than 2 in-Hg, install a new fuel pressure regulator valve and carry out the Electric Fuel Pump Pressure test to check fuel supply pressure.

If restriction is less than 2 in-Hg, inspect both fuel filters. Extremely clogged filters may appear black/brown in color or may exhibit structural damage or twisted paper. Some filters may be clogged from dust and dirt, which do not appear black. Install new fuel filters and carry out the Electric Fuel Pump Pressure test to check fuel supply pressure.

If restriction is less than 2 in-Hg, both filters and the fuel pressure regulator valve are OK, install a new fuel conditioning module and carry out the Electric Fuel Pump Pressure test to check fuel supply pressure.