Replace Your Mercury Optimax Dfi Air Injectors

Your Mercury OptiMax gets its performance and great fuel economy from the design of its Direct Fuel Injection System (DFI). An important part of this system is Mercury's Air Injector System. Your Air Injectors may need to be serviced and or repaired and this article may help.

Steps

  1. Read your engine owners manual.
  2. Purchase and read a factory shop manual.
  3. Review all safety precautions.
  4. Review Tips on various websites such as AirInjectors.Com
  5. Consult with your local Mercury Dealer or Certified Merc Tech.
  6. Perform a complete visual inspection of your engine.
  7. Check all harness plugs, fuel pressures and air pressures.
  8. Use a DDT (Digital Diagnostic Terminal) or CDS (Computer Diagnostic System) to properly test and diagnose which injector(s) may be faulty.
  9. Read your SmartTach's descriptive text to see which injector is faulty (not applicable to systems which do not have the SmartCraft Descriptive Test feature).
  10. Disconnect your battery(s) or turn off your battery switches.
  11. Very carefully release the fuel pressure from the schrader valve on the port fuel rail. See all precautions in your shop manual and below.
  12. Release any air pressure from the schrader in the starboard fuel rail.
  13. Remove all fuel injector harness plugs by depressing the plugs retainer clip and gently wigging the plug off of each fuel injector.
  14. Do not remove any of the rails air or fuel lines.
  15. Remove the two nuts which hold the rail in place with a 5/8" (15mm) socket wrench.
  16. Gently and evenly pry the rail away from the cylinder head.
  17. The Air Injectors can be seen between the rail and the cylinder head.
  18. Sometimes the Air Injectors will pull out with the rail. Other times they may stay fit into the cylinder head(s).
  19. gently twist the Air Injector and pull it out of the rail or head.
  20. Unsnap and remove the Air Injector harness plug.
  21. Use care to prevent moisture or debris from getting into the open holes in the heads and/or fuel rails.
  22. Discard the faulty Air Injector.
  23. Open the sealed pouch which contains the new Air Injector.
  24. Slip off the protective shipping cup off of the injector and immediately press the new Air Injector into the cylinder head hole.
  25. Snap the Air Injector harness plug onto the injector.
  26. Position the Fuel Rail in place and gently and evenly push it onto the head and air injectors.
  27. Fasten the Fuel Rail nuts and torque to spec as per your factory shop manual.
  28. Clip all the Fuel Injector plugs back onto each Fuel Injector.
  29. Visually inspect all your work.
  30. Install your battery(s) or turn on your battery switches.
  31. Supply adequate water pressure to your motor for test running on the garden hose. Follow your Owners Manuals instructions.
  32. Test run your motor and check for leaks and performance.

Tips

  • Read your engine owners manual.
  • Purchase and read a factory shop manual.
  • Review all safety precautions.
  • Review Tips on various websites such as AirInjectors.Com
  • Consult with your local Mercury Dealer or Certified Merc Tech.
  • Safety Comes FIRST!
  • Use good fresh fuel.
  • Only use Mercury Premium Plus of Synthetic DFI Oil.
  • Crummy oil will shorten the life of your Optimax Outboard.
  • Pick up some Mercury Quick Kleen fuel additive and add to your fuel system as per the directions on the bottle. Quick Kleen can make a huge difference in your engines performance when used correctly.
  • Never keep trying to run an Optimax with a faulty injector.
  • Clean and/or replace your Air Injectors after any major Air Compressor failures.
  • Air Injector seals will swell if left uninstalled for a few hours. Always replace the injector o-rings and Teflon seal.
  • Mercury makes a special seal installation tool and a special Teflon Seal resize tool.
  • Clean and remove any salt build up or corrosion.
  • Change your fuel filters every 50 to 100 hours of use.
  • Make sure you are using a battery with no less than 1000 MCA capacity.
  • For long trips, keep a spare Air Injector, Fuel Injector, Fuel Filters and a good tool set on board.

Warnings

  • Read your engine owners manual.
  • Purchase and read a factory shop manual.
  • Review all safety precautions.
  • Review Tips on various websites such as AirInjectors.Com
  • Consult with your local Mercury Dealer or Certified Merc Tech.
  • Safety Comes FIRST!
  • The Optimax has a very high output ignition system which can cause a terrific shock which could lead to injury or death.
  • Keep away from all moving parts such as belts, pulleys, trim and steering.
  • Remove your engines propeller after disconnecting your boats battery(s). A spinning prop can cause damage, injury or death.
  • Use extreme care when depressurizing the fuel schrader valve. Fuel will spray out under pressure. Use adequate skin and eye protection. Keep fuel away from all open flames, sparks or hot surfaces.
  • The Optimax has a computer (ECU) which can be damaged or ruined from even a small surge or short in your electrical system. Disconnect your battery(s) before unplugging any harnesses.

Things You'll Need

  • Eye Protection.
  • Set of mechanics tools.
  • Air Pressure Gauge.
  • Fuel Pressure Gauge.
  • DFI Seal Installation Tool.
  • Set of Air Injector O-rings and Teflon Seals.
  • New Air Injectors as needed (see airinjectors.com or your local dealer)
  • Factory Shop Manual (see servicemanuals.com)

Related Articles

  • Test for Mercury
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