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Tech Tip #58: Bleeding Lucas, Stanadyne, and Diesel Kiki Fuel Systems

Helpful tips for taking care of your fuel system

Modern high pressure Perkins and other diesel fuel systems are easy to work on if you follow three basics. These include ensuring personal safety, avoiding damaging a fuel line, and eliminating air from the system.

  • Safety – High pressure injection systems can easily blast diesel fuel beneath your skin, introducing a toxin into your body. Be careful.
  • Preventing damage – Perkins fuel lines can be hard to work on. Be patient, don’t over tighten connections, use new washers (“Coppers”) every time you change injectors, and for convenience sake always use remanufactured exchange injectors so the lines aren’t open for days while a local shop rebuilds your injectors.
  • Avoiding air – Most people introduce air into their system when they change their secondary fuel filter (the one up on the side of the Perkins engine). You can avoid this problem by always filling your fuel canister to the brim when you change the filters.

Bleeding Systems

There are two schools of thought on how to bleed a Perkins, Westebeke or other fuel system. One school says to bleed from the source (i.e., the tank) toward the injectors. The other school of thought recognizes that most air is introduced when you change fuel filters and suggests you start there. We think this is a good place to begin for this and the additional reason that air rises. To bleed the fuel filter loosen three turns the bleed screw on the IN side of the filter. Pump the priming lever on the fuel lift pump until fuel spurts out without any air bubbles. Retighten the screw and move on to the OUT side of the filter and repeat the purging process. The Perkins fuel lift pump primer can only be used up to the pump. From the pump to the injectors, the Perkins engine must be turned over. Then start the Perkins engine and see if you have eliminated the air.

If you still have air, bleed the injectors. Place the throttle in side open position while bleeding the injectors only. Loosen two only. Only open two injectors at a time while turning the engine during bleeding – or open the bleed screw if they have one (Perkins do not) – starting with the one nearest the high pressure pump. If all else fails, use a primer ball (same thing that’s on your outboard motor’s fuel line.) Insert the primer ball into the injector outlet line and pump the fuel through the system. Use the priming lever on the transfer pump until clear fuel comes out. Then move on to the other injectors. Then bleed the high pressure Perkins injection pump. Locate the bleed nipples. On a Perkins 4108 mechanical (not hydraulic) pump the upper bleed nipple is at the right corner of the pump as you face the side of the Perkins engine. Start through with the lower nipple directly below this one. Be sure the ESO of shut off solenoid are in the open position.

Want to learn more? Foley Engines has Perkins Workshop Manuals covering Lucas Mechanical and Hydraulic injector pumps ready to ship. We also have complete Lucas Workshop Manuals in stock. While we don’t recommend rebuilding your pump on your wife’s new granite counter tops, you might find this interesting reading.

Call us also if you need help with your injectors or fuel pump. We stock and have ready to ship exchange units that eliminate down time.

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