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  1. #1
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    Post Piggybacks and lean AFR at onset - lean spool fuel mode

    Just wanted to share a VERY interesting find that I came across while learning about the flash fuel control and fuel tables as it relates to the ever so interesting and many times discussed lean AFR at onset of WOT (as you get on it) and post shift. I've harped about this countless times before my ban on e90post indicating this as an issue/limitation with the piggyback fuel control which resulted in an eventual ban.

    This has always baffled me and always weirded me out on both the popular piggyback tunes (procede and the jb). I've talked many times about it with Shiv back in the day, not sure if I mentioned it to Terry, but basically my questions arose post-install of RBs while trying to dial in low RPM high load AFRs. No matter what you'd do on the procede OR on the JB the initial low RPM AFR with the RBs would almost always be higher than 13.5, 14 or even leaner. This is also the case on stock turbos (not as noticeable) and also noticeable on Shiv's latest Procede AFR logs (see FBIS' procede logs).

    Basically the reason the N54 is so hard to richen up below a certain RPM down low is due to a special fuel mode it runs there. It is called lean spool mode, very common thing on many platforms. Therefore, going WOT while actual boost is significantly lower than target will make the DME switch from normal fuel mode to lean spool fuel mode. DME purposely, because of its stock programming, will make AFR run in accordance to a special fuel table while turbos are spooling to speed the spool up, up to a certain RPM where lean spool mode won't be allowed.

    If any of you have ever wondered why we see lean spikes at the onset of WOT with the piggies, or post shift for that matter, its the DME intervening and going into LEAN SPOOL fuel mode prior to the boost reaching target Click here to enlarge

    Is this lean spool mode a problem with the piggies? I think DI is the saviour there and its obviously working out fine. Is it better to have direct control over it? Definitely a cleaner approach BUT if you can get around it with a piggy then as far as the motor is concerned it doesn't care how you provide it with the fuel as long as fuel is there. All in all, no drama, just really glad to have come to the root cause of this N54 behaviour.

    Cheers

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    Good lord the things I could say. The ability to set max rpm for lean spool mode is a beautiful thing Click here to enlarge

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    Here's the Former_boosted_is datalog from the 654whp single turbo run. Notice the AFR funkiness at WOT onset?

    Click here to enlarge

    Click here to enlarge

    Here's a log from my car with RBs when I ran the procede, older procede version but same issue back then, this time only 13psi:

    Click here to enlarge

    Another one off my car back in the day:
    Click here to enlarge
    Last edited by dzenno@PTF; 06-16-2012 at 06:15 PM.

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    Mind if I share this over on the other forum? I don't think it'll last long, but we'll see
    Click here to enlarge
    MOTIV750, MOTIV P-1000 PI, MOTIV/FUEL-IT! low pressure fuel system, AEM EMS/COBB AP, Aquamist HFS-3, ETS FMIC, SPEC stage 3+ clutch/SS flywheel, BC Racing coilovers and VMR wheels wrapped in Hankook RS3s.

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    Most tuning systems have "tip in" fuel enrichment and I'm sure the MSD8X is no exception. But the issue with post shift and spool up fuel trims (if you consider it an issue) is a little more fundamental. The starting point for fueling is the open loop tables. Those are extended up to 34% via learned fuel trims. Then the piggyback further extends it with a fuel pressure bias. But the starting point for these additives is always the open loop tables. During spool up and post manual shift load reported back to the DME is very low, so the open loop tables call for a relatively small amount of fuel. A low starting point means even with the additives for fuel trims and bias we just can't get as much fuel out of the DME as we might like in those instances. When the DME thinks its making 1psi and its actually making 7psi there is only so much you can do.

    But generally speaking I don't see fueling as much of an issue for 480-500rw with meth, even with the leaner tip in. Beyond that I think having a flash loading that corrects the open loop tables the right way is the way to go.
    Burger Motorsports
    Home of the Worlds fastest N20s, N54s, N55s, N63s, S55s, and S63s!

    It is the sole responsibility of the purchaser and installer of any BMS part to employ the correct installation techniques required to ensure the proper operation of BMS parts, and BMS disclaims any and all liability for any part failure due to improper installation or use. It is the sole responsibility of the customer to verify that the use of their vehicle and items purchased comply with federal, state and local regulations. BMS claims no legal federal, state or local certification concerning pollution controlled motor vehicles or mandated emissions requirements. BMS products labeled for use only in competition racing vehicles may only be used on competition racing vehicles operated exclusively on a closed course in conjunction with a sanctioned racing event, in accordance with all federal and state laws, and may never be operated on public roads/highways. Please see http://www.burgertuning.com/emissions_info.html for more information on legal requirements related to use of BMS parts.

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    Click here to enlarge Originally Posted by rader1 Click here to enlarge
    Mind if I share this over on the other forum? I don't think it'll last long, but we'll see
    Sure, no copyright

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    Well, it works...
    Why make a mountain out of a molehill?

    I think we all need to stay focused on what's important...
    GT-R R35 ​coming up...

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    Click here to enlarge Originally Posted by Terry@BMS Click here to enlarge
    Most tuning systems have "tip in" fuel enrichment and I'm sure the MSD8X is no exception. But the issue with post shift and spool up fuel trims (if you consider it an issue) is a little more fundamental. The starting point for fueling is the open loop tables. Those are extended up to 34% via learned fuel trims. Then the piggyback further extends it with a fuel pressure bias. But the starting point is the open loop tables. During spool up and post manual shift load reported back to the DME is very low. So the open loop tables call a relatively small amount of fuel. Low starting point means even with the additive for fuel trims and bias we just can't get as much fuel as we might like in those instances. When the DME thinks its making 1psi and its actually making 7psi there is only so much you can do.

    But generally speaking I don't see fueling as much of an issue for 480-500rw with meth, even with the leaner tip in. Beyond that I think having a flash loading that corrects the open loop tables the right way is the way to go.
    To call something truly an "issue", at least in my books, it'd HAVE to cause engine problems which obviously given countless miles on the N54s this doesn't, at least at these boost/power levels. The point of starting this thread, at least for me, was to put an end to something I've discussed and asked about many times and never really got a clear answer on as to why.

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    I'm a little surprised FB has the "issue" though. Aren't they reflashing the DME anyway?
    Burger Motorsports
    Home of the Worlds fastest N20s, N54s, N55s, N63s, S55s, and S63s!

    It is the sole responsibility of the purchaser and installer of any BMS part to employ the correct installation techniques required to ensure the proper operation of BMS parts, and BMS disclaims any and all liability for any part failure due to improper installation or use. It is the sole responsibility of the customer to verify that the use of their vehicle and items purchased comply with federal, state and local regulations. BMS claims no legal federal, state or local certification concerning pollution controlled motor vehicles or mandated emissions requirements. BMS products labeled for use only in competition racing vehicles may only be used on competition racing vehicles operated exclusively on a closed course in conjunction with a sanctioned racing event, in accordance with all federal and state laws, and may never be operated on public roads/highways. Please see http://www.burgertuning.com/emissions_info.html for more information on legal requirements related to use of BMS parts.

  10. #10
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    Click here to enlarge Originally Posted by Big Tom Click here to enlarge
    Well, it works...
    Why make a mountain out of a molehill?

    I think we all need to stay focused on what's important...
    I'd rather know WHY and HOW something works. But the fact that it doesn't break anything, at least as of yet that I know of, is definitely comforting Click here to enlarge

  11. #11
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    Click here to enlarge Originally Posted by Terry@BMS Click here to enlarge
    I'm a little surprised FB has the "issue" though. Aren't they reflashing the DME anyway?
    I wouldn't classify it as an "issue" at all, just AFR behaviour outside of the tune's control. To me, what he's GOT right now is a BEAST, which he'll need to learn how to drive Click here to enlarge and i hope he does so soon at a track

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    Click here to enlarge Originally Posted by Terry@BMS Click here to enlarge
    I'm a little surprised FB has the "issue" though. Aren't they reflashing the DME anyway?
    I was thinking the same thing, but didn't want to bring it up over there and get an infraction/ban. Seems strange even with his fuel pump upgrade and single turbo base flash he still can't get cobb like afr's.

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    So the AFR spike from 12 to 13AFR at 4k rpm is from this latest Vishnu Single Turbo dyno:

    Click here to enlarge

    At 4k rpm he's already at 15psi it seems from the 1st two Procede logs above which, looking at the dyno, is already peak torque (i.e. 490-500wtq) with pump+meth, and around 440wtq on just pump.

    Again, not saying this will blow the engine or anything even remotely like that. Just pointing out AFR behaviour that the DME imposes on the piggy which a piggy based tune such as Procede just simply cannot control as they're not reflashing the DME.

    I'm not flaming anything here, once again. I'm merely pointing out a limitation which I always have pointed out and I'm just glad I now finally know the exact reason as to WHY.

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    Click here to enlarge Originally Posted by shiv@vishnu Click here to enlarge
    AFAIK, there is no "lean spool" feature active in the MSD80/81. At least not in the traditional sense. I believe what most people are seeing is the partial load/low RPM AFR targets (which are considerably leaner than high load/high RPM AFR target) and the time it takes for the closed loop fuel control system to reach them during a dynamic load swing.

    FWIW, here is the AFR table in a stock DME:
    Click here to enlarge
    Shiv, the software you have sees only a limited number of tables in the DME. There are 2 AFR target tables, 1 fuel pressure table, and a lean spool table, along with a number of compensation and limits tables.

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    Click here to enlarge Originally Posted by dzenno Click here to enlarge
    Shiv, the software you have sees only a limited number of tables in the DME. There are 2 AFR target tables, 1 fuel pressure table, and a lean spool table, along with a number of compensation and limits tables.
    Actually, there is 1 lambda table, 2 lambda limiter tables, and several other fuel related compensation/FP tables. I don't believe what you refer to as the "lean spool" table works the way you are suggesting it does. But this is just based upon my experience tuning these engines at various power levels with all available tuning options.

    Shiv

    PS. The screen shot you are seeing is from an open source ROM editing software. It's age/version has nothing to do with the available maps/definitions since I created the XML file based upon info that I received. Probably from the same sources as your friends at Cobb Click here to enlarge
    Last edited by shiv@vishnu; 06-16-2012 at 08:13 PM.

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    Click here to enlarge Originally Posted by shiv@vishnu Click here to enlarge
    Actually, there is 1 lambda table, 2 lambda limiter tables, and several other fuel related compensation/FP tables. I don't believe what you refer to as the "lean spool" table works the way you are suggesting it does. But this is just based upon my experience tuning these engines at various power levels with all available tuning options.

    Shiv
    I can't discuss what u believe or not but i can tell u there are many tables you simply dont have access to with that seemingly ancient flash software you're using

    EDIT: then all u need to do is figure out what this table is and how to get to it...easy right?
    Last edited by dzenno@PTF; 06-16-2012 at 08:15 PM.

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    I agree with dzenno about the DME having multiple fuel tables. This is something more so available to flash tuners

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    dzenno,

    Nice find! Yet another proof that flash tunes can have much better control over fueling and ignition over the piggies.
    From all the things I've lost,
    I miss my mind the most!
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    shiv is too much, first he claims lean spool mode doesn't exist, someone shows a screen shot that it does, then shiv says "oh we call it something else." Click here to enlarge

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    Click here to enlarge Originally Posted by bmw335iguy Click here to enlarge
    shiv is too much, first he claims lean spool mode doesn't exist, someone shows a screen shot that it does, then shiv says "oh we call it something else." Click here to enlarge
    Semantics at it's best.....Click here to enlarge

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    I believe the proper term is "spin control". Lord Voldemort is a master of it, much like certain Apple execs.
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    Click here to enlarge Originally Posted by shiv@vishnu Click here to enlarge
    I think you are making some unfair assumptions. My only point that I have been trying to make from the start is that it is not a conventional "lean spool" table as it has been described (and apparently named in your Cobb software). But the name of the table is irrelevant if you know how it works. Here's the table I believe you are referring to in my rom editing software. The values in the table will be different from what you have in yours I'm guessing:

    Click here to enlarge
    Lol..no Shiv that is also not the lean spool table..it doesnt really matter if you have access to it or not and some open source software capabilities of reading a lambda table were ALSO not the point of this thread but i do see the reason why you're continuing down this discussion path..

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    ecu over piggyback

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    Dzenno - Did you figure out what tables to tune in the Cobb AP to correct the lean condition during spool up?

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    Click here to enlarge Originally Posted by boosted-M Click here to enlarge
    Dzenno - Did you figure out what tables to tune in the Cobb AP to correct the lean condition during spool up?
    AFR, and disable lean spool toggle. Done. Keep in mind the DME is going to achieve whatever the target AFR is for LOAD ACTUAL.

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