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Drop in Boost from 15 to 10psi without reason.

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  • Drop in Boost from 15 to 10psi without reason.

    Hey Brains Trust.

    My boost has dropped from 15psi to 10 and I cant seem to pin point why.

    If I take off the boost climbs and the car accelerates but as boost hits 10psi, it's like the car is detuning. Can you feel the car run out of legs.
    Fuel economy is a little worse and the car is lacking some power.

    I've checked the intercooler hoses, vacuum lines, filters, snorkel. I've cleaned the maf and map. Checked and drained the catch can. The stepper motor seems to move smoothly, doesnt make any grinder or clicking noises.

    No codes are being thrown. I dont have a chip.
    Boost is being read by both obd and saas gauge and as noted previously, boost used to hit 15ps. Now it doesnt.

    Any ideas?>

  • #2
    Replaced the map filter. Not that.


    • #3
      Modern diesels are a different beast to old style mechanical injection diesels, you won't get boost OR fuel unless all factors are met, that is for example engine temp, air intake temp, throttle position, load, etc. If you have limited boost something is missing, as you have not mentioned black smoke which would indicate excess fuel for the boost level I would be checking the fuel supply.
      Change fuel filters and check fuel lines as a restricted fuel supply may not cause a fault code but will cause the engine management system to restrict boost to the fuel supply level.
      Check fuel supply & injector pressures via OBD if you can.

      02 VX, Toyota Alloy Bar, IPF 900XS with 50 watt HID, 50 mm Lift- Lovell Shocks n Springs, Safari Snorkel, large Pioneer tray, Pioneer In-dash, Alpine roof mount DVD screen -handled the Simpson and Innaminka roads, now with a little TRD blower & Unichip


      • #4
        Hey Leethal,

        yeah slowly ticking off one item at a time.
        Was just hoping someone would be like "oh yeah check this, always breaks"

        Replaced fuel filters today and checked all intake hoses, EGR is dirty but still surprising good still after a clean from 80k km ago.
        Cleaned all sensors and blew out vacuum lines, intake is good with a new filter.

        Not sure what I can check on OBD. I've got the tools, any suggestions on what pressure I should be looking for?
        I'll run some injector cleaner through it as well.


        • #5
          So further developments. Attached is a screen grab from torque at 100% throttle under load accelerating on flat.
          you can see that the throttle position is only going to 70%. Ive checked the movement and its free moving and smooth.


          • #6
            throttle position sensor ?


            • #7
              Well after further cleaning and checking I'm stumped.

              fuel filter and map filter changed
              vacuum lines checked and cleaned.
              intercooler hoses checked
              exhuast checked
              Injector resistance checked
              fuel lines cleaned
              maf cleaned.
              Stepper motor works fine.

              symptoms are.
              boost not coming on unless full load and throttle.
              increased fuel usage
              very mild soot build up around exhuast.
              boost peaks at 8psi.
              Catch can oil build up
              engine runs and sounds normal
              exhaust gas temp appears
              Driver is going slowly insane.

              think ill need to head to a workshop. Time to loss those saving.


              • #8
                Well thats it. ive gone crazy.
                took the rig to united fuel and they say is fine. Boost is fine and power and torque is fine. They put it in the dyno and is making what they expect. Cant remember the hp or kw but 440nm. The curves look good so too do the fuel pressure and injectors.

                i use the car and is slow and sluggish boost is late and slow to come on.

                i feel like im in a ward telling at the staff. Im not the crazy one.