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Thread: Injector pulse width & duty cycle

  1. #11
    Lifetime Member 5.7ute's Avatar
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    No matter what the fuel pressure is doing, a raise in VE and or maf should increase IBPW(Then IDC will follow)
    A log with maf airflow etc and a tune file would help. (Before & after the increase in airmass)
    The Tremor at AIR

  2. #12
    Lifetime Member swingtan's Avatar
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    Just had a thought.... Any chance this vehicle uses "dual speed pump mode" ? As the Aus guys would know, certain Holden vehicles had an issue with the PCM dropping power to the pump at WOT which would give this problem.

    RE: adjusting the VE / MAF..... Yes, raising the values should see a rise in IDC, but if the fuel pressure dropped further ( due to less back pressure from the injectors being open longer ) then final AFR may not move too much.

    BTW, 5.7, did you actually pick up 50hp just by going to the 3" and retuning?

  3. #13
    Lifetime Member 5.7ute's Avatar
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    Quote Originally Posted by swingtan View Post
    BTW, 5.7, did you actually pick up 50hp just by going to the 3" and retuning?
    Yep, around 50rwhp.
    There was an issue with the intermediate pipes between the cat & tailpipe where the exhaust guy used press bends on the original 2 1/2 system. When I upgraded to 3" I had this section remade with mandrel bends here at work. FWIW there was around a 20rwhp increase over no pipes, but I will have to wait to I go down south at xmas again to confirm. Both dyno's I have access to give similar results within 2 rwkw (one a DD the other a mainline)
    The Tremor at AIR

  4. #14
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    Well sorry i left out a few important details guys, its an 02 zo6 with exhaust and a procharger D1 at 10 PSI, stock fuel systems, many people told me the system would be enough, i had my doubts. I did think like you 5.7 no matter what the fuel pressure the pulse width should go up, i only had the ve at 120 but also increasing the maf would get more fuel but it only went up by 1 millisecond. I tune ford and dodges quite a bit, only due a few corvettes a year so i am not familiar with how fast the injectors can pulse like older fords will go too almost 33 ms, where new ones only about 29-31 and dodges will go up too 32-33. So when this car didn't seem to increase from 15.5ms to 17.2 with adjustments to the maf i thought that was odd. Another this is the 12000 hz get hit quickly with a ford it would fail the meter and cause a problem.

    I know that i should use a custom operating system but i am unsure how it will react with the car, if anything might go away like the Heads up display or anything like that.

    here is a log file2002_60lbs_zo6procharger_idle_okpull_547_lean.efi
    David McLain
    www.etdrag.com

  5. #15
    Lifetime Member 5.7ute's Avatar
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    Looks to me like you are pegging the maf. Easy test would be to scale the maf, Ve & IFR & timing tables & do another pull.
    I have come across a N/A car with a stuffed fuel pump that I could still get to commanded AFR with 39psi ( WOT fuel pressure). In your case it appears that the lack of fuel pressure has caused you to inflate the airmass tables too high causing the limit to be hit.
    The Tremor at AIR

  6. #16
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    Yes that could have been it, raising the maf too much. When you say scale the maf i don't see any tables to rescale or i am missing them?
    David McLain
    www.etdrag.com

  7. #17
    Lifetime Member 5.7ute's Avatar
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    There is no actual scaling tables. What you would do is drop B0101,B5001 & B4001 by the same percentage. Basically telling the pcm that there is less air & the fuel injector flows less so that the injector is still opened for the right amount of time. Timing needs to be modified as the pcm will show less air & you would now have too much timing from the discrepency.
    I have to go quickly but will be back in 1/2 hr if you have any more questions.
    Last edited by 5.7ute; October 21st, 2010 at 04:26 PM.
    The Tremor at AIR

  8. #18
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    Just to add to the last post. If this is an auto there are some trans tables that will need modifying as well since airflow is used in the torque calculations. Hopefully someone familiar with auto tuning could add to this.
    The Tremor at AIR

  9. #19
    Senior Member Sid447's Avatar
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    Quote Originally Posted by etmotorsports View Post
    Checked the fuel pressure its dropping from 62 to 42 at the end of the run...but the pulse width and duty cycle are not climbing.
    Had the same thing here recently and it turned out to be a dying pump.
    Though even serviceable stock pumps can't maintain nominal pressure at constant high load/rpm (one guy here was running a modified LS7 in a VE SS and ran it at 260+ kph for a stretch and in spite of it being SD & OL it broke through lack of fuel.

  10. #20
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    Installed 255 pump and wiring kit, fuel pressure is good now, pulse width is still only going to 15.5-16 and running lean at 5800 and up too 6200, have raised the maf to its limit, raised the map ve to 139 or so which should be more than enough, and raised PE to 11:1 or so, since the maf is hitting 13411 hz which is just below failing, it will not increase the pulse width, there must be a table i am missing that is responsible for fueling? On a good side the car made 627 RWHP with better air today that last week, what a difference 20 air temp makes and holding the fuel pressure too, up until the limit was hit it made more power above 5500 the more fuel was added. I even tried another 02 sensor on the dyno to make sure it wasn't that they are within .1 of each other.
    David McLain
    www.etdrag.com

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