Injection pump starting device

Discussion in 'Diesel Engines' started by CDK, Apr 25, 2008.

  1. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    My VW turbo diesel engines (see post in DIY marinizing) have mechanical injection. The Bosch pumps have some sort of choke lever that - according to the documentation - increase the minimum amount of fuel injected and shift the injection timing.
    At the time of installation I contemplated using bowden cables or solenoids to pull these levers but decided against it in the expectation that the function would only be required in winter when the boat will not be used. Instead I installed knobs directly above the pumps.
    It turns out that while air temperatures have risen considerably, starting is still somewhat cumbersome without pulling these "chokes". The engines do start but stall 2 or 3 times because the idle rpm is too low.
    Is there any technical ground why the levers cannot be fixed in a position where starting is guaranteed and the idle rpm stays low enough to cause no damage to the gearboxes?
     
  2. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    The extra fuel required to start a cold engine is needed , even at warmer temperatures.

    The cylinders do not seal as well and the lower cylinder temperature requires extra fuel to ignite. With a diesel the ignition is very temperature sensative , and only efficient with a warmed up engine.

    Run the cable , there cheap and needed.

    Extra fuel after warmup will only cost money and require more frequent oil changes.

    FF
     
  3. CDK
    Joined: Aug 2007
    Posts: 3,324
    Likes: 148, Points: 63, Legacy Rep: 1819
    Location: Adriatic sea

    CDK retired engineer

    Thank you for answering FastFred.
    Let's discuss about the implications of feeding some extra fuel.
    As you know, a diesel always works at full throttle, because there isn't any. Only the amount of fuel determines the rpm, so feeding a bit more will inevitable increase idle speed once operating temperature is reached. But why the extra lever and why change the injection point? I could use the normal throttle control to increase rpm so the engine doesn't stall after starting and pull it back after a couple of minutes. But the manufacturer spent money on a separate lever, a bowden cable and a knob, so there must be a good reason for it. I've never owned a VW transporter, so I don't know how the engine behaves if you forget to push the 'choke' back in while driving.

    In my boat I do not use any bowden cables. Gear shift and throttle control are electronic; by choice, not necessity. Should the startup device be necessary I would do it the same way, I just hesitate because of all the work it involves: it needs more force to move the lever than a small solenoid can supply, so I would have to make another set of linear actuators.
     

  4. FAST FRED
    Joined: Oct 2002
    Posts: 4,519
    Likes: 110, Points: 63, Legacy Rep: 1009
    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    "Only the amount of fuel determines the rpm, so feeding a bit more will inevitable increase idle speed once operating temperature is reached. But why the extra lever and why change the injection point?"

    The ability of the engine to burn the fuel changes with cylinder temperature , so extra is required because its not warm and igniting properly.

    The timing is changed because the goal is to get the engine operating , not operating efficiently ,just to KEEP operating till it gets warmed up enough to accept the "normal" more advanced timing and fuel quantity.

    A push pull cable may not be electronically fancy , but it sure is cheap and efficient.

    FF
     
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