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How to check/adjust turbo boost pressure on a diesel

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  • How to check/adjust turbo boost pressure on a diesel

    I have recently been asked this question and I think the answer should problably go in the FAQ if a mod could please arrange it.

    I want to check the boost pressure on my 94 maestro td how do i do this and how do i increse it if need be.
    Ok fairly simple to do.

    You'll need a length of screen washer tubing (from the front of the engine bay into the car where you are going to put the gauge) and a screen washer tube T piece and also a boost gauge. You can fit this permenently or temporarily as you see fit.

    On the top of the injection pump you will see a black plastic tube running down from near the top on the right hand side. If you trace this tube down it will connect to a smaller diameter metal tube that runs along the front of the block and then round to the back of it ( it eventually ends up connecting into the turbo).

    If you cut this black pipe then fit the screen washer t-piece into it. The spare connection is then covered with screen wash tube and this is fed into passenger compartment through a rubber grommet somewhere and then connected to the boost gauge.

    There is no point checking the boost whilst stationary as the engine won't reach full boost when stationary usually.

    Standard boost is 13-14PSI (around 1 bar if you have a metric gauge). This boost is achieved when running flat out at high RPM.

    To adjust it there are a couple of ways of doing it:

    For both you'll need to loosen the 10?mm locknut on the turbo waste gate actuator rod

    Then you can either:
    Remove the circlip from the waste gate arm and pull the actuator rod off of the arm. Then screw end either up or down the rod to adjust the boost pressure. Then refit it back onto the waste gate arm

    You can grasp the rod with molegrips etc then rotate the rod inside the bit that clips to the wastegate

    Change the boost one whole turn at a time as a rough guide.
    Shorten the rod to increase the boost pressure and lengthen it to decrease it.

    The first method is the one I use as I find it easier although it requires a bit of force to stretch the actuator to refit the rod back onto the wastegate arm. (you'll be pulling against the spring preload of the actuator)

    If anyone else has any comments please feel free to add them before it gets FAQ'd - The Tickford Maestro Turbo Register - The Rover 200/400 (R8) Owners Club - My Rover Diesel Site

  • #2
    Does adjusting the boost in this way affect performance at all? My logical mind tells me that it should not, unless more fuel is injected.

    Presumably higher boost = more air so with the same fuel it would mean less emissions. Is that right?


    • #3
      The fuel pump has a device in it which senses the boost air pressure (the air pipe for this is where we add the t-piece to measure the boost pressure) and so injects an appropriate amount of fuel, (i.e. fueling off boost is much less than when on boost and it is supposed to be a progressive change from one state to the other). So if you increase boost pressure you can to some extent also increase the amount of fuel you stuff in aswell.

      It isn't quite as simple as that however and it depends on how the pump has been set up whether there is any more fuel enrichment adjustment left when you up the boost. There are a number of things to optimise all at once which is one of the reasons why my tuning a diesel FAQ is taking so long!

      However what I will say is that my van was boosting at 0.4bar when I measured it and when adjusted to 1.0 bar it ran a lot better however it still needs some more fine tuning, oh and that intercooler fitting too! - The Tickford Maestro Turbo Register - The Rover 200/400 (R8) Owners Club - My Rover Diesel Site