814098 1 Mercury SERVICE MANUAL

High Fuel Pressure
Excessive fuel pressure can cause fuel filter gaskets to rupture. The following conditions can cause high fuel pressure:
Plugged orifices in the fuel pressure regulating valve
Stuck fuel pressure regulating valve in the fuel transfer pump
Pinched fuel return lineChecking Fuel Pressure
Table 1
Required Tools
Part Number Part Name Quantity
1U-5470
or
198-4240 Engine Pressure Group
or
Digital Pressure Indicator 1
Illustration 1 g00293196
1U-5470 Engine Pressure Group
Refer to Special Instruction, SEHS8907, "Using The 1U-5470 Engine Pressure Group" for more information.
Illustration 2 g02561516When using the 198-4240 Pressure Indicator Tool Group, refer to Operating Manual, NEHS0818, "Using the 198-4240 Pressure Indicator Tool Group" for more information.
Fuel leaked or spilled onto hot surfaces or electrical components can cause a fire. Clean up fuel spills immediately.
Keep all parts clean from contaminants.Contaminants may cause rapid wear and shortened component life.
Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting, and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids.Refer to Special Publication, NENG2500, "Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on Cat products.Dispose of all fluids according to local regulations and mandates.
Use the following procedure in order to measure the fuel pressure that is after the secondary filter: Note: Fuel pressure readings near the fuel supply manifold have pressure spikes. The pressure spikes are caused by excess fuel that is returning to the fuel system from the injectors. Excessive needle movement at the gauge may be present. Connect the gauge with a section of suitable hose. The air in the hose absorbs the spikes. This action achieves an average reading and a steady needle. Keep the gauge above the measuring point.
Illustration 3 g02324296
Standard secondary fuel filter base
(1) Input fuel line from transfer pump
(2) Output fuel line to head
(3) Test port
Install the 1U-5470 Engine Pressure Group into test port (3). This port is the proper test port.
If excessive pressure is found, check the conditions that are listed previously under the "High Fuel Pressure" heading.
Use the following procedure to check the fuel pressure if the engine will not start or if hard starting is a problem:
Crank the engine and check the fuel pressure after the secondary fuel filter. Refer to Step 1
The fuel pressure should be 50 kPa (7 psi) minimum at 120 to 180 rpm. Record the pressure.
Use the following procedure to check the fuel pressure if there are other problems:
Adjust the engine speed between low idle and high idle with no load. Refer to Engine Technical Marketing Information - TMI Web, "Test Spec".
Check the fuel pressure after the secondary fuel filter. Refer to Step 1.
The fuel pressure should be within the range specified between low and high idle. Refer to Engine Technical Marketing Information - TMI Web, "Test Spec". Record the pressure.
Illustration 4 g02825937
(4) Fuel pressure regulating valve
(5) Return line from the cylinder head (Input)
(6) Check valve
(7) Return to tank (output)
Use the following procedure to inspect the return pressure regulating valve to the fuel tank:
Return fuel pressure regulating valve (4) is located above the ECM.
Inspect return fuel pressure regulating valve (4).
The return fuel pressure regulating valve may be stuck or worn. Remove the check valve (6). Inspect the check valve. If contamination is not found and the fuel pressure regulating valve is worn out, then replace the fuel pressure regulating valve. If dirt is found, clean the check valve assembly and reinstall the check valve assembly.