DB2 Tuning Guide

Discussion in '6.9L IH & 7.3L IDI Diesels' started by Thewespaul, Sep 17, 2018.

  1. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    For a long time the 7.3 and 6.9 DB2 injection pump has been a "magic box" that you didn't mess with other than some fuel screw adjustments. This guide will help you to get the most out of your stock pump, without dropping the coin on a modified pump.

    *Before making any of these adjustments, it is critical that you install a pyrometer and a boost gauge. These adjustments are not for a naturally aspirated engine, but only for engines with a turbo that can use the large amount of fuel a stock pump is capable of delivering.

    **These adjustments are not complicated, but they require the cleanliness of a heart surgeon. Any debris that enters your fuel system at any of these points of adjustment can be lethal for your injection pump and injectors
    .
    Perform these adjustments at your own risk.

    The first and most common adjustment is the "fuel screw" this adjustment limits the amount of fuel that the injection pump delivers throughout the entire rpm range. So if you adjust the screw to deliver 15% more fuel, then you will have 15% more fuel available at 3000 rpms, or at 300 rpms when you are cranking. This adjustment can be used to prolong the life of your pump if you are having hot start issues, but will give you higher egts as a side effect, so keep that in mind. Also, remember that this adjustment only increases your maximum fueling, so its not going to ruin your fuel economy unless you are always using the extra fueling.

    This adjustment is quite simple, and there is already an excellent write up in the tech articles here:
    https://www.oilburners.net/threads/turning-up-a-db2-injection-pump.59187/

    The only thing I have to add, is once you have made this adjustment once, and you have the engine at the correct location, make a mark on your balancer where it lines up with the your timing mark so you can easily get to it again. This adjustment tends to give around 25 cc increase, but varies greatly with pump wear.

    The next adjustment that can be made is the "minimaxx" rod. This rod runs through the center of the governor assembly and controls your minimum and maximum rpms. This adjustment is on a sliding scale so as you increase your maximum rpm, your minimum rpm increases as well, and vise versa. Because of this, in most cases you will need to lower your idle with the adjustment screw on the the throttle bracket/lever. Since rpm is controlled by fueling in a diesel, I have found that taking this adjustment all the way in has net 10 ccs of fuel (20% increase) with the allen bottomed out on its lock nut and up to 15ccs with my custom locknut that gives you further adjustment in the minimaxx assembly:
    2C4838EC-EF5B-4B26-BD04-C7351EF375C7.jpeg
    (To show difference in locking nut width)

    To adjust this first locate the screw in the back of the injection pump, circled in red here:
    DFF7F723-FE2E-4181-8E6A-EDD44E3C5BF0.jpeg
    Break the locking nut loose with a 1/2 wrench, then screw the allen in with a 3/16 hex. Tighten the locking nut down to 7 ft lbs and check idle rpm. I will be making a seperate thread on installing and adjusting the minimaxx with my custom locknut, I will link it once I have posted it.

    The next adjustment is only on late model cases (92 and up) and is known as the torque screw on the internet, but on most pumps this is referred to as your "pre-boost fueling" adjustment. This adjustment (circled in blue in above picture) was added to limit low rpm fueling in an attempt to better match federal emissions requirements. This is a very helpful adjustment to limit the amount of smoke you get before your turbo produces boost. If you are trying to get the most fuel possible then you can break the lock nut loose and back the screw all the way out. This only net a 5 cc increase on the test bench at peak, but increased low rpm fueling significantly more. If you do not have this adjustment then you effectively have this maxed out already. I am working on a kit to modify your case to add this adjustment, as well as a making it "on the fly" adjustable, allowing you to tune in the smoke while you drive or change elevation.

    That is it for the adjustments I was able to test today on the test bench but I will add as I continue testing, I have a few adjustments I have found make a decent difference, but I dont want to advertise them until I have had a chance to test them on the test bench as well.

    Now for some mods, for these you will need an electric lift pump with an adjustable pressure regulator because you will need to be able to add fuel pressure to compensate for these changes. The pump housing has a fitting here:
    BBEAD466-4F4F-426E-A02D-A4C1D8BD501E.jpeg
    This fitting effectively has guts that act as a pressure relief valve to restrict the amount of fuel the pump returns to tank, as well as to hold a small amount of pressure in the housing. You can remove this fitting and replace it with a straight through barbed fitting, or you can knock out the guts with a punch and small hammer. This picked up 5ccs of fuel across the entire rpm range, but the biggest improvement is the amount of fuel that returns from the pump, with more fuel passing through the housing there is more fuel available to cool and lubricate the pump, prolonging the life of the pump, and helping to prevent heat soaking issues. Because there is less restriction, more fuel is required to supply the pump, hence the electric fuel pump and regulator being a requirement.

    All in all, with my custom minimaxx locknut installed, I took a stock DB2 with 208k miles and severe hot starting issues, and made 107 ccs peak fueling. Im sure a fresh pump with new plungers would be capable of much more, but I wanted to test this on a "worst case scenario" pump.
     
    Last edited: Sep 17, 2018
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  2. bad67ford

    bad67ford Registered User

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    Good write up, its good to see guys experimenting and sharing the results with us so we can get the most out our idi's

    thanks and keep up the good work
     
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  3. Tristan

    Tristan Full Access Member

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    Awesome! Thank you Wes


    Sent from my iPhone using Tapatalk
     
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  4. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    Thanks gents!
     
  5. Clb

    Clb Another old truck Supporting Member

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    Nice work...
    And I thought the standyne db2 pamphlet I posted would be useful, yours is easy to do thanx
     
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  6. The_Josh_Bear

    The_Josh_Bear Full Access Member

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    I second that!!! Thank you very much for the clear and easy-to-follow write-up! :Thumbs Up
    Did you get the 107cc's out of that pump with just these external mods?
     
  7. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    That is correct, the pump previously just barely made 60 ccs as it came off the truck with no adjustment.
     
  8. The_Josh_Bear

    The_Josh_Bear Full Access Member

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    Holy free fuel pump tuning Batman!
     
  9. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    Hopefully this info is useful and saves some folks some money!
     
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  10. genscripter

    genscripter Full Access Member

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    While we're on the topic of adjusting IP's, what is the functionality of the bottom set-screw on the driver's side?

    Macrobb made a video of this once, and I wanted to know more about what it does.
     
  11. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    That is for the advance arm, that gets adjusted when you are initially setting up the pump on the test bench. The screw allows you to adjust how soon in the rpm range the arm starts moving, and by clocking the faceplate you can change how much it retards in total. I’m working on a new faceplate that has less timing down low and more advance higher up.
     
  12. hce

    hce So can i.... Supporting Member

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    I may know someone who can help with that. Just another toolpath to remove some more material on the high side. Surface finish would be much better then this one.

    20180918_061953.jpg
     
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  13. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    I might take you up on that. Local guy quoted me $400 for what I wanted done, I thought that was quite high.
     
  14. saburai

    saburai Full Access Member

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    Thanks for doing what you do.
     
  15. Garbage_Mechan

    Garbage_Mechan Garbage Mechanic

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    Man this is getting good!
    I have a 6.9 apart that is already ported and studded.
     
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