Results 1 to 4 of 4

Thread: Pulse Width Calculations

  1. #1
    Member
    Join Date
    Jun 2009
    Posts
    50

    Default Pulse Width Calculations

    No answers in my search…

    Without a wide band O2 sensor, how do we have any assurance that our PW’s are close enough for good power without going overboard and wasting fuel?

    Garrett web site claims 22:1 AFR is good for power with little to no smoke. B.S. flags?

    Anyone calculating desired PW using injector flow rates combined with rail pressure to match air flow rates for a sanity check in their tunes/logs or am I way behind the learning curve?
    I know this is pretty well sorted out by the tuners but I’m curious how you build a PW table.

  2. #2
    Lifetime Member THEFERMANATOR's Avatar
    Join Date
    Mar 2009
    Posts
    800

    Default

    With a diesel your air fuel ratio isn't really that important IMHO. Watch your EGT's and make sure they are under about 1400 pre turbo. As far as how low you can go, some have checked and gone down to 11:1 on the ratio. I know I just built up a 20% over pulse table(ramps up from 10mm3 to 120mm3 to 20% over), and I set it up to reach close to 120MM3 of fuel on the top end whereas stock would only hit around 100 in those areas. And it didn't even hardly haze with only 25 pounds of boost.
    1995 GMC 2500 SUBURBAN powered by 01 DURAMAX/ALLISON, little of this, a little of that,
    DIAMONDEYE 4" exhaust, CORSA muffler, AFE stage 1 dry filter, custom tuning by me, KENNEDY single pump and pump rub kit.

  3. #3
    Member
    Join Date
    Jun 2009
    Posts
    50

    Default

    I was wondering if a spread sheet like Josh's timing table would be useful. The advantage is that there would be fewer variables... I think.
    In theory you know how much air (Lb/hr) it takes to support a given HP for a given displacement and at what RPM, etc.
    You also know the fuel required (Lb/hr), and injector flow rate for a given PSI per hr.
    Can you convert those figures to a fuel per revolution and divide by 8?
    Wait, do you divide by 8 to get PW?
    I’m struggling a bit with this as my answers aren’t passing the common sense test.

  4. #4
    Lifetime Member killerbee's Avatar
    Join Date
    Jan 2006
    Posts
    1,079

    Default

    I think your question is best answered with the "equivalence ratio" custom pid. You will probably find a calcpids file in this diesel forum if you search for that term. It is essentially a fuel/air ratio.
    Michael, Systems Engineer 04.5 D-max LLY, Phoenix, Arizona Email
    Custom Tuning Services
    DURAMAX/CUMMINS ECM's TCM's for sale, all years, 20% wholesale discount available
    EFILive's first VGT "Software Wastegate Tune"

Similar Threads

  1. Pulse width down-duty cyle up?
    By VHR in forum Petrol / Gas
    Replies: 3
    Last Post: September 22nd, 2011, 08:07 AM
  2. Small Pulse Adjust/Low Pulse Width Injector Offset
    By N0DIH in forum General (Petrol, Gas, Ethanol)
    Replies: 0
    Last Post: September 4th, 2007, 09:05 AM
  3. Injector pulse width
    By Bruce Melton in forum General (Petrol, Gas, Ethanol)
    Replies: 5
    Last Post: October 7th, 2006, 01:49 PM
  4. Minimum Injector Pulse Width
    By curtbriggs in forum General (Petrol, Gas, Ethanol)
    Replies: 11
    Last Post: May 11th, 2006, 11:28 AM
  5. Pulse width Modulation???
    By vetteboy2k in forum 4speed RWD/FWD Transmission Tuning (incl T42)
    Replies: 5
    Last Post: June 25th, 2005, 01:41 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •