Mercury 200 OptiMax Jet Drive, Service Manual, Page: 192 / 391

Direct Fuel Injection
90-8M0050731 MAY 2011 Page 3B-29
Component or Problem Possible Causes Corrective Action
Fuel pressure is low or fuel
pressure drops while running
Electric fuel pumps, VST,
or filters
Ensure that the lanyard switch is in the correct position.
Air pressure remains normal Turn the ignition switch to the "RUN" position. Both electric
pumps should operate for two seconds. If they do not run, check
the 20 amp fuse and wire connections.
Replace components as necessary.
Electric fuel pumps, VST,
or filters
If the pumps run, but have low fuel pressure, remove the drain
plug from the vapor separator tank (VST) and inspect for fuel.
If the VST does not contain fuel:
Prime the system (primer bulb) and check the water separator
for debris. Clean/replace as necessary.
If the bulb primes the fuel system, perform a vacuum test on
the pulse pump.
If there is still no fuel in the VST, check all components prior to
the VST for restrictions.
If no restrictions are found, inspect/replace the water separating
fuel filter.
If there is still no fuel, inspect the VST filter and needle/seat for
contamination or obstruction. Replace as necessary.
Fuel pressure is low or fuel
pressure drops while running
Electric fuel pumps, VST,
or filters
If the VST contains fuel:
Air pressure remains normal Pinch the fuel return line to the high‑pressure fuel pump/VST.
The pressure at the fuel test valve should exceed 110 psi.
If necessary, check the high‑pressure pump amperage draw (in
series).
Normal draw is 6–9 amps. If the draw is below 2 amps, check
the fuel pump filter at the base of the pump for debris.
If filter is clean and the draw is below 2 amps, replace the pump.
If the draw is above 9 amps, replace the pump.
Lift pump Check the fuel lift pump for output. Normal output is 1–2 psi at
idle, 1 psi minimum.
Service/replace if necessary.
Anti‑siphon valve Check for restricted fuel flow.
Fuel test (Schrader) valve Damaged valve. Replace the valve with a Fuel Valve Kit.
Fuel pressure is high and air
pressure is normal
Fuel regulator Inspect the fuel regulator hole for blockage. Clean or correct as
necessary.
Inspect the diaphragm seat and rail for damage. If the fuel
regulator is faulty or incorrectly calibrated, replace the port fuel
rail.
Inspect the diaphragm seat and the rail for damage. Replace
the rail as necessary.
Fuel and air pressure are both
high
Air vent hose Remove the air vent hose at the rail and check air pressure at
idle. If the pressures return to normal, the air vent hose is
blocked or otherwise restricted.
Inspect the air vent hose to the air plenum for blockage or kinks.
Clear or correct as necessary.
Air regulator Check the air pressure regulator for blockage or kinks.
Clean or correct as necessary. If the air regulator is faulty or
incorrectly calibrated, replace the port rail.