NOTE: 5P2720 Self-Sealing Probe Adapter and 5P2718 Pressure Probe may be used with the tools needed, to allow installation of pressure probes in the future.
1U5470 Engine Pressure Group
The 1U5470 Engine Pressure Group can be used to check engine fuel pressures.
This tool group has a gauge to read fuel pressure to the cylinder head. Special Instruction, SEHS8907 is with the tool group and gives information for its use.
Fuel Return Line
(1) Tube assembly (fuel transfer pump to fuel filter). (2) Tube assembly (fuel filter to fuel gallery). (3) Fitting (fuel return to tank). (4) Regulating orifice and check valve. (5) Cylinder head. (6) Fuel gallery. (7) Fuel outlet port.
Fuel pressure at the inlet to the secondary fuel filter (8) should read between 400 and 525 kPa (58 to 76 psi) during normal operating conditions under load. At low idle, fuel pressure at the filter inlet (8) should read from 400 to 435 kPa (581 to 63 psi). Fuel pressure to the cylinder head fuel gallery (6) should be as above, less the delta P across the secondary fuel filter.
Pressure drop across the secondary fuel filter is typically at least 35 kPa (5 psi) with a new filter. As the filter accumulates deposits, the pressure differential will increase. If fuel pressure in the fuel gallery (6) at the injectors decreases to approximately 69 kPa (10 psi) misfiring may occur.
An orificed check valve (4) is mounted directly at the fuel return port at the rear end of the fuel gallery in the cylinder head. The orifice maintains fuel pressure at low engine speeds, and the spring loaded check valve prevents drainback of the fuel from the head after engine shutdown.
Fuel Pressure Test
(8) Fuel pressure tap (unfiltered). (9) Fuel filter base. (10) Fuel pressure tap (filtered).
To check the unfiltered fuel pressure, remove the plug from fuel pressure tap (8). Install the connector, seal and 1U5470 Engine Pressure Group to fuel pressure tap (8) to obtain transfer pump pressure. Operate the engine. To check in the main gallery for pressure, remove the plug from fuel pressure tap (10). Install the adapter, seal and 1U5470 Engine Pressure Group to fuel pressure tap (8). Operate the engine.
NOTE: Make sure the fuel filter is clean before checking fuel pressure. A restricted fuel filter will cause lower fuel pressure at tap (10) than at tap (8).