Cummins C8.3 Fuel Transfer Pump - R & R

The fuel transfer pump is the gizmo that gets the fuel from the fuel tank to the engine.  It sounds like such an obvious task, but it's complicated by the distance between the tank and engine as well as the fuel filters.  The fuel tank in the typical diesel pusher is 20 feet or more from the engine.  The fuel pump doesn't just have to get the fuel to travel that far, it has to suck the fuel through the primary filter first.  Then, it has to pump the fuel through the secondary filter on its way to the fuel injection pump.  And since diesel engines pump much more fuel through their fuel systems than they burn, the fuel transfer pump has to move a lot of fuel.  When it gets weak, the engine doesn't get as much fuel as it needs so it loses power and/or the fuel system components don't get all the cooling they need.  Either way, it's not a good thing to have a fuel transfer pump that's not working 100%.

The fuel transfer pump is located on the left side of the engine.  Remember, the front of the engine is Cylinder #1 even if its backwards in our pushers.  That means that the left side of the engine is on the right side of the coach.  Got it?  If you're still confused, just look on the side opposite the exhaust manifold.  The pump is bolted to the side of the engine block, below and slightly forward of the OEM fuel filter mount.  If you're still confused, just look at the pictures.

  1. As always, cleanliness is next to Godliness when working on a diesel fuel system.  Start by cleaning everything around the fuel pump and especially all the fuel lines, their connections and the pump itself.  Don't forget to put a pan or tray under the coach before you rinse the guck off the side of the engine.
  2. Use flare wrenches  on the fuel line connections to avoid rounding the corners of the fittings.  You won't need them very often, but if you mess up a fitting using your good ol' crescent wrench, don't say I didn't warn you.  If you don't have a set of flare wrenches, get them now before you start.  Sears has them for a fair price.

  3. Take photos of the way it looks now.  Your engine might not look quite like mine, and you might want to refer to those photos later.  If you don't take photos now, Uncle Murphy may drop by just to annoy you.

  4. Move the throttle cable, transmission cable and anything else out of the way that you need to for access to the transfer pump.

  5. Loosen the fittings on the fuel lines.  I like to always break all the lines loose before I actually disconnect them.  That way, when I run into something that doesn't come apart I won't be getting crud into the line that I had opened up. 

  6. Disconnect the fuel lines from the transfer pump.  Wrap the open ends of the fuel lines.  Those blue mechanic's paper towels and rubber bands work well.

  7. Loosen the two screws that hold the fuel transfer pump to the engine block with your 10mm socket wrench.  Remove both screws and remove the pump.

  8. Clean off the gasket surface on the engine block.  A gasket scraper, putty knife or razor blade works well.  Just don't scratch the mounting surface or get pieces of gasket into the open hole in the block.

  9. Compare the old pump and the new pump

    1. Make sure you got the right pump
    2. Move any fittings from the old pump to the new pump    
  10. Hold the new pump in the area and begin to connect the fuel lines.  Leave them loose.  It's just easier to get the threads started when the pump can be wiggled around a bit to line things up. 

  11. Position the new pump with gasket against the block and start the mounting bolts.  OOPS!  The pump won't fit up against the block

    1. The lobe on the camshaft is 'up' and pressing against the pump push rod preventing the pump form fitting up against the block.  It will only get about 1/4" away and you can't press hard enough to make it fit.  
    2. Two solutions:
      1. Get out your engine barring tool and rotate the engine until the camshaft lobe allows the pump to fit up nicely against the block, or
      2. "Bump" the engine with the ignition key.  That means turning the key to the 'Start' position and immediately turning it back off.  If you are quick, the engine will rotate a bit and sooner or later you'll find a spot on the cam where the pump will drop into place.  If you aren't quick, the engine will start.  So, if you are going to try this technique make sure nothing and nobody is around anything that might move if the engine starts.  If it does start, it will immediately shut down because you remembered to turn the key off immediately.  You did remember, didn't you?
      3. If the idea of the engine starting while you're bumping it with the starter, then disconnect the fuel shut-off solenoid. 
  12. Tighten the pump mounting screws to the proper torque; 18 ft-lb for my C8.3.

  13. Now, tighten those fuel lines you left nice and loose in step 9.

  14. Reconnect anything else you might have disconnected to get access to the fuel transfer pump.

  15. Double check everything

    1. Are the fuel line fittings tight?
    2. Are the pump mounting bolts tight?
    3. Is the fuel-shut off solenoid connected?
    4. Are the throttle cable & transmission cable connected?
    5. Is there anything on or around the engine that shouldn't be?
  16. Start the engine

    1. Oh-oh.  The engine won't start.
    2. Did it start when you bumped it with the starter? 
    3. If so, you may have sucked some air into the fuel injection pump.
    4. Bleed the fuel system and it should start OK.


Updated: 03/12/2008

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