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Thread: Injector pulse width & duty cycle

  1. #1
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    Default Injector pulse width & duty cycle

    Stupid question is there a limit on the GEN III that limit the injector duty cycle to 80% or pulse width?
    David McLain
    www.etdrag.com

  2. #2
    Lifetime Member swingtan's Avatar
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    No "hard limit" in the tune as such. It's a limit imposed by the actual flow rate of the injector and the engine RPM. If the engine is turning fast enough that the injector cannot supply enough fuel, then you have hit the 100% IDC limit and the mixtures will lean out past that point. The 80% figure is considered the "safe maximum" to allow for things like transients and a safety margin.

    Simon

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    Lifetime Member 5.7ute's Avatar
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    Quote Originally Posted by swingtan View Post
    No "hard limit" in the tune as such. It's a limit imposed by the actual flow rate of the injector and the engine RPM. If the engine is turning fast enough that the injector cannot supply enough fuel, then you have hit the 100% IDC limit and the mixtures will lean out past that point. The 80% figure is considered the "safe maximum" to allow for things like transients and a safety margin.

    Simon
    X2.
    FWIW, if there was a hard limit for IBPW it would be 996ms. I would not like to think what the IDC would be up there lol.
    The Tremor at AIR

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    I am seeing 81% duty cycle and i cannot get any more fuel it seems a/f goes lean at the end of the run but duty cycle doesn't go up, i am using the stock operating system keep adding fuel via the MAF but no significant increases, does the VE table still control the fuel even if the you are up in the RPM range and above the throtle position for the MAF to take over?
    David McLain
    www.etdrag.com

  5. #5
    Lifetime Member mr.prick's Avatar
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    This depends on how the tune is set up.
    {B0120} determines when the MAF table is in control.
    SD will have the MAF removed, provided the MAF was failed properly.

    Make sure your WBO2 is functioning properly.
    I've had bad sensors show no change in WOT AFR even after adding fuel.
    If adding fuel shows no change to WBO2 readings this maybe the case.
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  6. #6
    Joe (Moderator) joecar's Avatar
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    Post log files.

  7. #7
    Lifetime Member swingtan's Avatar
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    X2 on the logs, also a copy of the tune would be good....

    You can think of IDC as the percentage of time the injector is open, compared to the time it takes for 2 engine revolutions ( or the time from when the inlet valve starts to open, until the next time it starts to open). This second "time" is the maximum amount of time the injector has to supply fuel for a single induction cycle. If the injector is on for the whole of this time, then IDC=100% and you have lost control of fueling.

    If you are having issues with IDC, then the exhaust AFR would follow the gm/Cyl trace on a chart. As total airflow increased, AFR's would lean out and then should richen up as the airflow drops after peak torque.

    Simon

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    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.
    David McLain
    www.etdrag.com

  9. #9
    Joe (Moderator) joecar'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.
    The pressure drop is causing reduced flowrate, and that is the reason why it goes lean.

  10. #10
    Lifetime Member swingtan's Avatar
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    Yep, that will be it. Time to check filter, regulator and pump......

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