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Thread: B4005 Small Pulse Adjust How does GM create this table?

  1. #1
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    Default B4005 Small Pulse Adjust How does GM create this table?

    I've looked at a lot of GM files...B4005 has many differnt "looks" depending on what car /injectors it's in. It's not a standard slope.

    I've had to change mine bigtime to get 86lb low imp injectors to work in COS5. I've watched some of the changes by using RR in realtime....

    I'm getting close but would like to understand the small pulse adjustments better. The nice thing about the table is that it will command an adder where you want it....plus it can be a negative adder which is nice with big injectors.

    It and the voltage oddsets are the keys to big injector tuning.

  2. #2
    Lifetime Member SSpdDmon's Avatar
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    Quote Originally Posted by onfire
    I've looked at a lot of GM files...B4005 has many differnt "looks" depending on what car /injectors it's in. It's not a standard slope.

    I've had to change mine bigtime to get 86lb low imp injectors to work in COS5. I've watched some of the changes by using RR in realtime....

    I'm getting close but would like to understand the small pulse adjustments better. The nice thing about the table is that it will command an adder where you want it....plus it can be a negative adder which is nice with big injectors.

    It and the voltage oddsets are the keys to big injector tuning.
    Please elaborate more on tuning for offsets and pulse adjusts....

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    Only time I needed to adjust the spa,vof,etc was for the 86lb injectors. The 42lb svo's and the 60lb Mototron worked well with a proper VE table and a proper IFR table. The 86lb low imp injectors require more tuning. Basically they are so large that if you only adjust the VE and the IFR the minimum pulse at idle is around 1.8ms.....this is too much for a 14.7:1 idle....I was getting 11.5:1 too rich.

    Did not matter if I set the Minimum pw to 0.6 and the Default pw to 0.6...I still could not get the ecm to go lower than 1.8pw at idle.

    So you are forced into altering the offsets. Basically they are adders. You start with a base pulse width and you add to that with the voltage offset and the spa offset....together it makes the minimum pw around 1.8 So you have to lower the offsets to get the minimum pw lower. By lowering both table I now can get a 1.38pw at idle and can go as lean as 16 :1 if I want it.

    I'm just curious if anyone knew how GM calculated their spa curve. I had to do mine with trial and error based on RR feedback in realtime and a wideband.

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    Lifetime Member SSpdDmon's Avatar
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    I asked because I noticed the same problem with my SVO's during decel prior to DFCO kicking in (and they're only 30's). No matter how much I lopped off the VE/IFR/MAF tables, I'd get a rich condition (13.5:1). Min. PW was in the 1.8ms range too. I think it may also be contributing to a rich condition below 1600rpms. I'd be very curious to know how as well how GM got their numbers...

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    hmmmm this is VERY interesting!!

    Listening in....

    From the sound of what has been stated it almost seems that the SPA is being used to patchwork anamolies in the injector.

    In onfire's case, it sounds like he is watching what frequencies are hitting the injector [miliseconds/pwm] and adjusting for how the frequencies [miliseconds/pwm] are affecting the injector. IS THAT WHAT THIS IS???

    Adjusting for the frequency of the signal?

    Thank you.
    Last edited by 2002_z28_six_speed; July 18th, 2007 at 04:40 AM.

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    Quote Originally Posted by 2002_z28_six_speed
    hmmmm this is VERY interesting!!

    Listening in....


    How tight is the variance on this aftermarket injectors? If you put in one set would the table numbers work for the next? I am sure they bench flowtest them. Just asking.

    Thank you.
    I had mine flowmatched at Racetronix so they would be within 1%.

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    Changed my post a little bit after I stared at the table for awhile. Sorry.

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    flow if the injector is not linear, it has at least 4 distinct stages with 4 different fueling rates. first is the offset stage, when the injector is building up working against the spring, so there's no flow yet. second is the opening stage, at which the injector is changing the flowrate. third is the 'proper' fueling at a rate dictated by the rated flow, operating fuel pressure and manifold vacuum (if not referenced). fourth is the closing stage, when the injector goes from full flow rate to zero.



    the actual fuel mass injected is the 'area under the curve' of the various fuel rates in time of injection (integrate from 0 to IPW across the four different functions for IFR).

    if you look at ford tuning, they treat it as two stages, they actually have two flow rate numbers, and a 'breakpoint' which is the time the first fuel rate is used for, and everything after that is calculated with the second fuel rate. of course ford tuning people with their natural tendency of 'screw the numbers, right is whatever works' attitude tweak the numbers randomly until they get it to the point where the fueling is acceptable.

    GM did it differently. Once the airmass is obtained (SD calcs or MAF lookup) the fuel mass needed is airmass*AFR. the PCM knows the IFR value at the current MANVAC so it uses that to get the pulsewidth it thinks it should use (IPW=fuelmass/IFR). however, this is wrong, because that's assuming the IFR at the various stages of the time of injection is the same, and it isn't (paragraph #1). the design people knew that, thus created a 'lets make up for the discrepancy with another table' table this is the short pulse adder table.

    short pulse adder is the time required (at the official IFR) to make up for the difference in the expected fuel mass, and the fuel mass that actually goes in. at long pulse widths, the areas with the non-official IFR account for a small portion of the total fuel mass, thus are just ignored. however at short pulse width they make up a significantly larger portion of the fuel mass, thus cannot be ignored. That's why we have the short pulse adder.

    there's also the offset table, that seems to be mostly dependent on the physical characteristics of the injector (resistance?), operating MANVAC and voltage. offset seems to always get added to the pulsewidth, long or short.

    i'm working on a spreadsheet that will convert injector data into short pulse adder table. this is the best explanation i've been able to come up with. of course it might be all horsepoo, so please let me know if i'm full of it. if you got better explanations/data please let me know so we can get this short pulse adder spreadsheet done quicker, we need the fueling to be more precise and this should help a lot.

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    Lifetime Member SSpdDmon's Avatar
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    What I think I know -

    When it comes to injectors, there's 3 main factors to pay attention too:

    1) When the injector opens (which I thought was offset)
    2) How long it stays open (IPW)
    3) How much fuel is dumped (IFR)

    From what I've read, the software allows us to alter flow rate based on injector performance and 'offset vs. ECT' in the timing tables. Then there's the SPA and the IPW voltage adjustments are simply adder tables to the base IPW, which is calculated using other sensors/tables.

    I haven't read anything about adjusting the timing of the injector vs. the ECT. All I've seen is people posting some offset vs. voltage tables for various injectors, which typically commands a bigger pulse width. My problem is, I can't shake the rich decel condition I have from my SVO 30's even with the stock voltage correction table.

    I'm losing train of thought....I'll be back later. We definitely need to crack this puzzle though. :lol:

  10. #10
    Joe (Moderator) joecar's Avatar
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    So is B4005 the area under the sloped parts of that curve...?

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