8A - Tandem Fuel Pump Pressure

8a. Tandem Fuel Pump Pressure





Purpose:
To determine if there is sufficient fuel pressure for correct engine operation.









Recommended Procedure:
Note if operator has indicated if the high fuel restriction lamp has been illuminated. A restricted fuel filter may be causing low fuel pressure.

Connect High Fuel Pressure Adapter 01400931-3 or equivalent to the Schrader valve mounted in the fuel regulator block on the side of the fuel filter housing. Connect a line for a 160-psi gauge to the adapter. Run the engine at low idle and check for leaks in the line to the gauge. Operate the engine at wide open throttle (maximum engine speed out of gear with the brakes set and the wheels blocked). Measure maximum fuel pressure and compare to specification.

Repeat for front and rear tanks.

Change the fuel filter if the pressure is low and retest. If fuel pressure is still low, go to Performance Diagnostic Procedures Step 7b and check restriction from the fuel tank.

Possible Causes:
- A fuel filter could cause high restriction and low fuel pressure because of dirt or fuel jelling in cold ambient temperatures. Change filter and retest. It may take a couple of crank cycles to purge the air out of the fuel system.
- Debris in the fuel regulator valve will cause low fuel pressure. Disassemble, inspect and clean.
- A kinked or severely bent fuel supply line or blockage at the pickup tube could cause restriction and therefore low fuel pressure.
- 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.
- The fuel pump could have internal damage, e.g., ruptured diaphragm, seized plunger or leaking check valves.

Tools Required:
- 0-160 psi fuel pressure gauge
- High Fuel Pressure Adapter 014-00931-3 or equivalent line with 1/4-inch NPT fitting