How to Repair and Replace a Yanmar Diesel Injector

Written by prescott harvey
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How to Repair and Replace a Yanmar Diesel Injector
(jet engine detail image by Andrew Breeden from

Some injectors will begin to perform improperly after just 1,000 hours, causing smoke, knocking and poor engine performance. As a rule of thumb, repairing and replacing diesel engine fuel injectors should be left to trained professionals. Injectors must be perfectly aligned to function. Their nozzles are smaller than a grain of sand, and clogging them is easy. Any removal of a diesel fuel injector is more likely to exacerbate the problem. That said, it is possible to remove, clean, and reinstall them.

Skill level:
Moderately Challenging

Things you need

  • WD-40
  • Screwdriver
  • Crescent wrench
  • Paper towel
  • Replacement washers
  • Carburettor cleaner

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  1. 1

    Locate your fuel injectors. You will find one, possibly two, fuel lines attached to your fuel tanks. Follow the outgoing (as opposed to the intake) fuel line, past any fuel filters (there may be one or two), to the fuel pump. After the fuel pump, the line continues to each of the injector heads. The number of fuel injectors corresponds to the number of engine cylinders.

  2. 2

    Using the crescent wrench, loosen and remove the nut that connects the fuel return line to the fuel injector. Then loosen and remove the nuts that attach the fuel injector to the engine.

  3. 3

    If the injectors are stuck, use WD-40 to loosen any corrosion. Use the screwdriver for added leverage until the injector slides out.

  4. 4

    Use a paper towel to clean the injector hole of all carbon deposits. You can reattach the intake fuel line and manually crank the engine to test the spray of your injector. Any drops of diesel or a mist angle of more than 30 degrees indicates an obstruction in the nozzle.

  5. 5

    If the nozzle is plugged, immerse it in carburettor cleaner (taking great care to keep everything clean). This will break down the carbon deposits.

  6. 6

    Reinsert the fuel injector into the engine block, re-tighten the nuts to the engine block, and reattach the fuel lines.

  7. 7

    Repeat for each fuel injector.

Tips and warnings

  • When testing the spray of your fuel injectors, open the engine's decompression valves. This removes the pressure in the chambers, making it easier to manually crank the engine.
  • Fuel injector nozzles are EXTREMELY vulnerable. It is highly recommended that you hire a professional to service them.
  • Make sure your engine is off before attempting this.
  • If the engine's decompression valve is engaged, make sure to manually turn the engine very slowly. Otherwise it might catch and the engine will start.
  • Have some diesel rags handy to absorb the run-off when you disconnect the fuel lines.

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