2. Perform the fuel pump load test with CDS G3.
3. The reading on the fuel pressure gauge should be within specifications.
High‑Pressure Fuel Pump
Fuel pressure, engine not running 340–370 kPa (49.3–53.7 psi)
Fuel pressure, engine running at idle 290–340 kPa (42.1–49.3 psi)
Fuel pressure, engine running under load
Pressure dependent on manifold vacuum pressure, use calculation (refer to
Fuel Pressure Calculations, Engine Running)
4. If there is little or no pressure reading on the gauge, ensure the fuel supply module has enough fuel to supply the
high‑pressure fuel pump. It may be necessary to prime the fuel supply module to verify the system is purged of entrained
air. Refer to the previous procedure to ensure that the fuel lift pump is operating properly.
Fuel Pressure Calculations, Engine Running
A simple formula can be used to determine what the approximate fuel pressure should be at different points in the engine RPM
range: (MAP – Baro) + regulator set point.
IMPORTANT: The actual regulator set point will vary according to engine fuel consumption. The actual fuel pressure may
therefore fall anywhere within a 90 kPa (13.04 psi) range. In other words, fuel pressures calculated with this formula have a
tolerance of ± 45 kPa (6.52 psi).
The following examples assume an ambient barometric pressure of 98 kPa (14.21 psi) and an average fuel pressure set point
of 363 kPa (52.65 psi).
If CDS G3 displays a manifold absolute pressure of 38 kPa (5.51 psi), then:
•
kPa: (38 – 98) + 363 = 303. The calculated fuel pressure reading is 303 kPa; actual fuel pressure is 303 ± 45 kPa.
•
psi: (5.51 – 14.21) + 52.65 = 43.95. The calculated fuel pressure reading is 43.95 psi; actual fuel pressure is 43.95 ± 6.52
psi.
Fuel Injector Resistance Test
NOTE: A fuel injector test can be performed with the CDS G3 diagnostic interface tool.
Use a digital ohmmeter to test the resistance of the fuel injector.
NOTE: A resistance test can be performed while the fuel injector is mounted to the fuel rail. It is not necessary to remove the
fuel injector from the fuel rail when checking the resistance of the fuel injector. The fuel injector is not polarity sensitive.
Removed from fuel rail for clarity
a - Fuel injector pins
Fuel Injector
Resistance at 21 °C (71 °F) 12.5 ± 0.6 Ω
Troubleshooting and Diagnostics
Page 7B-4 © 2018 Mercury Marine 90-8M0146617 eng JULY 2018
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