Fuel Pressure and Air Pressure Troubleshooting

If you are experiencing issues with fuel pressure and air pressure in your Direct Fuel Injection Mercury Optimax 175HP DFI outboard, here are some troubleshooting steps you can take:

Fuel Pressure and Air Pressure are Both Low - Corrective Action

1. Inspect air compressor air intake for blockage.
2. Remove air compressor cylinder head and inspect for scuffing of cylinder wall. Inspect for broken reeds and/or reed stops.
3. Remove and inspect diaphragm for cuts or tears and seat damage on diaphragm.
4. Remove and inspect diaphragm for cuts or tears on diaphragm and rail.

Fuel Pressure Low or Fuel Pressure Drops while

1. Check the operation of electric pumps each time the key is turned to the RUN position. If they do not run, check the 20 ampere fuse and wire connections.
2. If pumps run but have no fuel output, check vapor separator for fuel.
3. If no fuel is present in vapor separator, check fuel/water separator for debris and crankcase mounted fuel pump for output.
4. Check high pressure pump amperage draw and low pressure output.
5. Remove and inspect diaphragm for cuts or tears in the fuel regulator.

Fuel Pressure High and Air Pressure is Normal

1. Check for a stuck check valve in the fuel return hose.
2. Look for debris blocking the fuel regulator hole and check for a faulty pressure gauge.

Fuel and Air Pressure Higher than Normal

1. Check for debris blocking the air regulator passage.
2. Ensure the air dump hose is not blocked or plugged.