Mercury MERCRUISER, Service Manual, Page: 90 / 566

Chart T2: Fuel System Electrical Test
Step Action Yes No
1
• Turn the ignition key switch on.
• Listen for the fuel pump to operate.
• Turn the ignition key switch off.
Did the fuel pump operate for 3–5 seconds?
No problem
found.
Go to step 2.
2
• Disconnect the fuel pump harness connector.
• Turn the ignition key switch on.
• Using the DMT connected to ground, check for battery voltage (B+) at
the fuel pump harness connector pin A.
• Turn the ignition key switch off.
With the ignition on, was B+ present?
Install a known
good fuel pump.
Retest system.
Reconnect the fuel pump
harness connector.
Go to step 3.
3
• Remove the fuel pump relay (FPR).
• Turn the ignition key switch on.
• Using the DMT connected to ground, check for B+ at FPR harness
connector terminal 30.
• Turn the ignition key switch off.
With the ignition on, was B+ present?
Go to step 4.
Locate and repair the open
or short in the harness.
Retest system.
4
Check for continuity between FPR harness connector terminal 86 and
PCM harness connector pin A‑2D.
Was continuity present?
Install a known
good FPR.
Retest system.
Locate and repair the open
or short in the harness.
Retest system.
Chart T3: Fuel System Diagnosis
IMPORTANT: Before starting fuel system diagnosis, verify that there is fuel in the tank.
Step Action Yes No
1
• Disconnect both battery cables from the battery.
• Install a fuel pressure gauge.
• Connect the battery cables to the battery.
• Turn the ignition key switch on.
• The fuel pump will operate for 3–5 seconds. Note the fuel pressure
while the pump is operating. The pressure may drop after the pump
stops, but should not drop immediately to 0 kPa (0 psi).
• Turn the ignition key switch off.
Was the fuel pressure within specification while the pump was
operating?
Go to step 2. Go to step 4.
2
Attempt to start the engine and allow it to idle.
Did the engine start?
Go to step 3. Go to step 5.
3
With the engine idling, connect an external vacuum source to the fuel
pressure regulator and apply 34 kPa (10 in. Hg) of vacuum.
Did fuel pressure decrease by approximately 34.5 kPa (5 psi)?
Problem is intermittent or
the fuel supply to the
engine is low or restricted.
Replace faulty fuel
pressure regulator.
Retest system.
4
Was fuel pressure present?
Go to step 5. Go to
Chart T2
.
5
Does the system establish fuel pressure and then quickly decrease
to 0 kPa (0 psi)?
Go to step 6. Retest system.
6
• Turn the ignition key switch off.
• Block the fuel pressure line between the fuel pump and the fuel rail.
• Turn the ignition key switch on.
Does the fuel pressure remain steady?
Locate and repair leaking
fuel injectors or fuel line
connections.
Go to step 7.
7
• Turn the ignition key switch off.
• Block the fuel return line using the fuel shut off valve tool.
• Turn the ignition key switch on.
Does the fuel pressure remain steady?
Replace faulty fuel
pressure regulator.
Retest system.
Install a known
good fuel pump.
Retest system.
Troubleshooting
Page 1D-20 © 2016 Mercury Marine 90-8M0099748 eng DECEMBER 2015