Chart T2: Fuel System Electrical Test; Chart T3: Fuel System Diagnosis - Mercury MerCruiser Service Manual

Troubleshooting

Chart T2: Fuel System Electrical Test

Step
• Turn the ignition key switch on.
• Listen for the fuel pump to operate.
1
• Turn the ignition key switch off.
Did the fuel pump operate for 3–5 seconds?
• Disconnect the fuel pump harness connector.
• Turn the ignition key switch on.
• Using the DMT connected to ground, check for battery voltage (B+) at
2
the fuel pump harness connector pin A.
• Turn the ignition key switch off.
With the ignition on, was B+ present?
• Remove the fuel pump relay (FPR).
• Turn the ignition key switch on.
• Using the DMT connected to ground, check for B+ at FPR harness
3
connector terminal 30.
• Turn the ignition key switch off.
With the ignition on, was B+ present?
Check for continuity between FPR harness connector terminal 86 and
4 PCM harness connector pin A‑2D.
Was continuity present?

Chart T3: Fuel System Diagnosis

IMPORTANT: Before starting fuel system diagnosis, verify that there is fuel in the tank.
Step
• 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
1
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?
Attempt to start the engine and allow it to idle.
2
Did the engine start?
With the engine idling, connect an external vacuum source to the fuel
3 pressure regulator and apply 34 kPa (10 in. Hg) of vacuum.
Did fuel pressure decrease by approximately 34.5 kPa (5 psi)?
4
Was fuel pressure present?
Does the system establish fuel pressure and then quickly decrease
5
to 0 kPa (0 psi)?
• Turn the ignition key switch off.
• Block the fuel pressure line between the fuel pump and the fuel rail.
6
• Turn the ignition key switch on.
Does the fuel pressure remain steady?
• Turn the ignition key switch off.
• Block the fuel return line using the fuel shut off valve tool.
7
• Turn the ignition key switch on.
Does the fuel pressure remain steady?
Page 1D-20
Action
Action
© 2016 Mercury Marine
Yes
No problem
found.
Install a known Reconnect the fuel pump
good fuel pump. harness connector.
Retest system.
Locate and repair the open
Go to step 4. or short in the harness.
Retest system.
Install a known Locate and repair the open
good FPR. or short in the harness.
Retest system. Retest system.
Yes
Go to step 2.
Go to step 3.
Problem is intermittent or
the fuel supply to the
engine is low or restricted.
Go to step 5.
Go to step 6.
Locate and repair leaking
fuel injectors or fuel line
connections.
Replace faulty fuel
pressure regulator.
Retest system.
90-8M0099748 eng DECEMBER 2015
No
Go to step 2.
Go to step 3.
No
Go to step 4.
Go to step 5.
Replace faulty fuel
pressure regulator.
Retest system.
Go to Chart T2.
Retest system.
Go to step 7.
Install a known
good fuel pump.
Retest system.