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HPDI High Pressure Pump Output; Thoughts?

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  • HPDI High Pressure Pump Output; Thoughts?

    The nominal pressure for the HPDI HP pump is 1015 psi. Plus or minus 217 psi. Yes friends and neighbors, 217 psi.

    If my math is correct 217 psi on the low side is over 20%. In theory that should also be 20% less fuel being delivered if and when the pump output is 798 psi. That would result is a much leaner air/fuel mixture.

    A lean air/fuel mixture is more prone to detonation than is a normal or rich air/fuel mixture.

    The HPDI does not utilize a knock sensor. Could this be a reason (one of many) for detonation that is seen somewhat often in a big block HPDI? Throw in a partially clogged injector and it will only get worse.

    Detonate a block, install a new block with the old pump and kablowey. There goes the new block.

    Just wondering why Yamaha does not call for a check of the HP pump when a big block HPDI shows signs of detonation? I stopped wondering years ago why there is no knock sensor. But there is a water is fuel warning.

  • #2
    No knock sensor on a 14000 dollar engine maka no sense to me, especially considering the way these engines are typically operated. How often do you see 4000 rpm in your truck? A handful of times per year, unless you're under 30 and a hot head. And even then, it's typically for a short duration. Not for 30 miles offshore.

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    • #3
      4000rpm? Bout every day.

      3.3 HPDI? Couple more years and will not be a topic. Hard to find one around here running in salt water.

      Wonder what the over/under specs on the DI F425 may be?

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      • #4
        I thought not all HPDI Yamahas ran 1015 psi, some were lower

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        • #5
          Originally posted by 99yam40 View Post
          I thought not all HPDI Yamahas ran 1015 psi, some were lower
          Only the big blocks (3.3 liter) run at 1015. Smaller motors use just one pump at about 750 psi.

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          • #6
            Pressure change and fuel flow are not directly proportional. I remember this from hydraulic class...I think. I used this flow calculator.
            https://www.deatschwerks.com/fuel-ca...ure-calculator

            Using nice round numbers I put in:

            - current fuel pressure 1000psi
            - current flow rate 100 lbs/ hour (made that up)
            -Then new fuel pressure of 800psi (low end of acceptable range)

            The new calculated flow rate is down to 89 lbs/hours.. Which is 11% difference not 20%.

            Works the same going the other way, increase the pressure to 1200 psi and the flow rate increases to 110lbs/hours, again about 10% difference In flow rate.

            So a 20% increase or decrease in pump pressure only changes the flow rate by about 10%.in this example.

            So if I am using the right calculator here, would a 10% different in the amount of fuel delivered cause a lean enough condition to cause knock?

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            • #7
              and as the ECU monitors pressure it can,and does, alter injector on time to make up for over/under nominal pressure.
              trons are fairly quick.

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              • #8
                Originally posted by rodbolt17 View Post
                and as the ECU monitors pressure it can,and does, alter injector on time to make up for over/under nominal pressure.
                trons are fairly quick.
                Does the ECU monitor for injector voltage? I don't think so but... Low voltage will also affect injector output.

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                • #9
                  yes, the injector driver looks at injector voltage. there is even a code for injectors.

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