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MS: 4 vs 2 injections/cycle

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    MS: 4 vs 2 injections/cycle

    To people with 550 cc injectors, do you guys run 2 or 4 injections per engine cycle?

    When I was NA with 230 cc injectors, I was running 4 injections/cycle and it was working great. Since I went turbo with 550s, I am only able to run 2 injections/cycle, I just can't figure out a map with 4 injections/cycle.

    It just looks to me that 4 injections is the most efficient way but I tried several values and the car doesn't even Idle, rpm oscillates, AFR oscillates, the car chokes. I'm using high Impedance injectors.

    Can someone running 4 injections with 550 post a screen shot of their fuel map? Req fuel for 550s is calculated to be 2.8. I just need the idle portion, I can figure out the rest.

    Thanks

    #2
    You cant use 4 squirts because with such large injectors the PW at idle is TINY. Trying to split that up into 4 squirts means that the injectors never actually open all the way due to the opening latency... this causes the wacky results you are seeing.
    Escort GTR -- 11.87 @ 117.6 mph -- 320 HP / 325 Ft. Lbs. @ 23 PSI
    ... The first FWD BG with a Toyota E153 transmission conversion in the USA!
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      #3
      with injectors that big, you should be running 2 squirts alternating anyway. If it was good enough for the stock ECU, it's good enough for your current setup

      And yeah, as Riel said, your PWs at idle running 4 squirts alternating are going to be so dangerously close to the opening time of the injectors that a teeny variation will cause massive fluctuation in how much is injected.
      Ask me about engine management!

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        #4
        I'm running 4 alternating injections per cycle with 550cc injectors. I had to use the hi-res code with MSI to achieve this.

        This GREATLY smooths out idle and tip-in and is well worth it. It also somewhat overcomes the fact that the MS does not time injection. Without the hi-res code this is not possible on 550cc injectors.

        I should also mention that I have RC low impedence injectors (running with a resistor box) which are well known for their shorter opening times and accuracy at small pulse widths.

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          #5
          Thanks guys, so I guess I'll need low impedance injectors then... I thought about that but wasn't sure. Idle with 550 is crappy and unless I put it to like 13.5, it afterfires, misfires and backfires.

          I'm using MS2 extra with one of the latest betas, should be as good as the high res code. Lex, is your Reqfuel (greyed box) 2.8? What's the approx. value in your fuel table at idle? I just want to try it with high impedance injectors, see how it behaves.

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            #6
            With 4 alternating injections my req fuel is 3.2

            Try it with your current injectors? It might work. You may have to adjust the opening time for the injectors.

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              #7
              thanks Alex, I'll try higher reqfuel but I doubt it would affect things since it's just a base multiplier.

              With 2 injections/engine cycle, the pulsewidth at idle is around 1.7 ms. Dividing this by 2 would be 0.85 which is less than my set opening time, set to 1 ms I believe. Isn't using lowZ injectors with a resistor box amount to roughly the same as using highZ injectors? MS can drive lowZ injectors alone what should give you better flexibility.

              One thing I noticed though is when using 4 injections/cycle, the engine needs less fuel to run and my AFRs became pig rich. (halved reqfuel, doubled values in table=>AFRs became 10.1).

              Comment


                #8
                Remember that opening time remains constant. You only divide the part that is "delivering fuel" of the pw by 2. So your new pulse width should be around 1.35ms.

                What you will find is that the opening time of 1ms is too large and the injector delivers fuel during this opening time causing the excessively rich condition. Trim it to somewhere between 0.95-0.98 and you should be able to achieve the same AFR as you did with 2 injections per cycle.

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                  #9
                  Interesting, so your are saying that the pulsewidth includes the opening time? That would explain the rich condition indeed. Edit: Just read the Megamanual, guess I skipped that part...

                  I actually didn't note the pulsewidth duration with the "New" map since I was concentrated on the AFR, should take a log of all that, hopefully tonight.

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                    #10
                    I just realized I did everything wrong. When you set the number of pulses to 4, you don't double the table since the number of pulses gets doubled, dooh...

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                      #11
                      Yes, you're not supposed to touch your VE table at all.

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