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  1. #1
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    Thumbs up HOT: N54 Fuel Limitation found in the DME operating system!...RESOLVED!

    First some background:
    As many of us know the N54 tuning has always mentioned fueling as a bottleneck and its been discussed many times on this and other boards. At first injectors were to blame, then HPFP, then recently the LPFP but some also alluded to fuel lines, etc. As piggyback tunes are/were more the more predominant choice of tune since the N54 came out we basically know today that there are definite limits as far as what you can do with fueling with a piggyback. This isn't much of a concern on stock turbo setups as those have proven to run reliably for many hundreds of thousands of miles on many N54s around the world. The issue starts to really become apparent as power is pushed past what the stock turbos can provide.

    Piggybacks use 2 things to control fuel:
    1) fuel pressure (aka open loop, where based on certain load params fuel pressure is raised to hit richer AFR target)
    2) front o2 wideband sensor voltage biasing (telling the engine its running leaner than it is so it injects more fuel through closed loop control).

    Piggybacks cannot change the following directly:
    1) Fuel injector timing/pulse width/duty cycle
    2) DME load based "logic" for fuel control -> STOCK N54 FUEL LIMIT IS BURIED IN HERE! Click here to enlarge

    The fuel limits we were seeing on piggybacks are neither fuel pumps, nor injectors, or fuel lines. The issue lies right in the DME's operating system logic. I'm just a messenger obviously but I'll try to explain what was just discovered by Rob and the boys at COBB in N54 DME fuel control logic.

    First a bit of background on RB Turbos and COBB:
    I've been running this flash for a while now with the JB4 stacked on top for additional boost when meth is flowing. The issue I encountered was that AFR would start to lean towards 13AFR towards redline on their most aggressive stage2+fmic map. Adding more boost on top with the JB4 would make this even more apparent. The way I dealt with it was to up fuel pressure using JB4's fuel pressure feature which would take care of it to a point but really it wasn't ideal as with considerably upped boost AFR really didn't look as great as when flash was working on its own. This puzzled Rob@cobb as the fuel handling is 100% closed loop on this car and the DME "should" be correcting for this, obviously provided that the fuel system wasn't hardware limited in some way.

    What they realized is that the DME has either a feature, a bug or a deliberate limitation imposed right in the operating system code to do with MAF calculations. Here's what Rob@Cobb had to say about this finding while testing with RB turbos:

    Click here to enlarge Originally Posted by Rob@Cobb
    I think I found a bug, feature, or very odd deliberate limit. I'm betting it's not the last one, but I digress. Fuel is staying where it should be when running the stage map I have been running.


    Several of the internal calculations use MAF, a calculated value. Two different calculated MAF values are compared together to create a calculated pressure that, way down the road, hits the fuel calculations. In short one of the values was being clipped above 290ish g/s. I fixed the clipping and all is well now.
    Basically the stock DME will not allow for more fuel past a certain point as it is not programmed to do EVEN when the tables are setup correctly, unless the logic for MAF calculation is fixed.

    With all that said, I got a new map from Rob to try on the car to see if the AFR stays on target without upping fuel pressure using the JB4..and it DID! Flat 12AFR across..

    This current race map runs higher boost than stage2+ (20psi down to 16-17psi at 6k rpm 15.5-ish at redline), stage 2 timing curve (6deg-10.5deg timing up top). On the Cobb Mustang dyno this was good for 440whp/465wtq on pump gas and 80/20 meth using the Aquamist HFS-3 kit and dual 1mm nozzles. If you take 8% (very conservative) correction to a typical Dynojet this is about 475whp/502wtq, at just 16-17psi at 6krpm where peak power is made so lots more room left. I was/am impressed at the numbers with such timing and boost curve.

    This is a huge win for N54 tuning in general and definitely a huge step in the right direction in terms of fueling the N54 for some BIG power numbers.

    Now that we know AFR is staying on target without drama its time to start cranking boost up and squeeze RBs by the ballzzz Click here to enlarge Cobb says that RB turbos provide for a cooler charge than stock turbos which makes sense given larger turbine and compressor and that more power is on tap...we're planning more boost, more timing will be added only for high octane as well...

    N54+Cobb 1, DME limitation 0

    Great job to Rob and all the guys at Cobb! Click here to enlarge

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    Great post. However, what does Rob estimate the fueling limit to be? And what kind of power do you think you can squeeze out on pump only reliably?

    I always said running methanol is a band aid for tune limitations so I am curious to see how far you can push the stock fuel system before you hit a physical limit.

    I remember having a conversation with laloosh last year on so-called load limits and news like this confirms those statements.

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    Hell yeah! Looks like HPF should be working with Cobb on their N54 project.

    I wonder if they could make an e85 map now....

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    Great write-up and that I'm glad to hear things are improving for the N54 platform.

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    Are there any ideas of what the true maximum fuel flow limitations are? After unlocking this capability?
    Some people live long, meaningful lives.

    Other people eat shit and die.

    I'm not racist, I hate everybody equally; especially fat people.


    Click here to enlarge

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    Wow great post! I'm wondering what the other tuners have to say about this...and if they have even come to the same conclusion?

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    awesome

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    Great post. It's going to be a fun year.
    Rob Beck Turbos, PROcede Rev. 3, Procede Fueling Flash (via OpenFlash Tablet), PPS Methanol System (DO12/Aquamist Flow Sensor), DCI, Quaife LSD, BMW Performance Suspension, Autobahn Exotics Exhaust, Helix FMIC, AR Design Downpipes, BSH Catch Can, Forge Diverter Valves, P3cars Vent Boost Gauge, Alufelgen CSL Reps, Lux 5.1 H8 Angel Eyes, HPB HID Fogs, LTBMW M3 Side Skirts, BMW M3 Rear Spoiler, BMW Front Aero Lip, BMW Pedal Kit, BMW M Shift Knob, Autotecknic Matte Black Grilles.

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    looks like we may see our first set of bent rods or something from legitimate point of just too much power now....but i guess thats a good thing cause now they can find out what the n54 can really do

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    Man what an epic few months its been. And more are in the future I'm certain. Big respect to Rob!

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    Called it a year ago.... Lol glad cobb is finally tuning the car and the n54 gets the tunning it deserves.
    wtf is hpf thinking going with a procede is beyond me.

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    Click here to enlarge Originally Posted by themyst Click here to enlarge
    Great post. However, what does Rob estimate the fueling limit to be? And what kind of power do you think you can squeeze out on pump only reliably?

    I always said running methanol is a band aid for tune limitations so I am curious to see how far you can push the stock fuel system before you hit a physical limit.

    I remember having a conversation with laloosh last year on so-called load limits and news like this confirms those statements.
    We'll see in terms of max power, those maps are under way...had to get this out of the way properly first as it was a limitation that would impact everything...as Rob said, this is the first fuel limitation hit and great its software and not hardware...hopefully next up is hardware and no more weird bmw back stabbing fuel limiter "features" in their operating system Click here to enlarge

    Click here to enlarge Originally Posted by SlicktopTTZ Click here to enlarge
    Hell yeah! Looks like HPF should be working with Cobb on their N54 project.

    I wonder if they could make an e85 map now....
    I can't agree more in terms of tune for a single turbo...flash is definitely starting to sound like a better choice with time especially in terms of proper fuel control

    Click here to enlarge Originally Posted by DBFIU Click here to enlarge
    Are there any ideas of what the true maximum fuel flow limitations are? After unlocking this capability?
    The only thing that we know is that with the MAF fix described above the initial fuel limitation has been removed...obviously we'll know more if/when another fuel limit is hit, only maybe this time a true hardware one but we'll see...

    Click here to enlarge Originally Posted by DarkPhantom Click here to enlarge
    Wow great post! I'm wondering what the other tuners have to say about this...and if they have even come to the same conclusion?
    Piggybacks have no way of changing/viewing this information so you wouldn't hear it from that camp. In terms of flash tuners no one has spoken about it before and as far as we know so far the others have just remapped some "popular" tables...in any case, who knows, doesn't matter really...what matters is that platform is moving forward in the right direction..

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    I also love how shiv pretty much banned for arguing load limits with him. He said they don't exist as they can be altered by the procede. $#@! you again scum bag. I feel better now

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    As for this limit I believe georgesmooth spoke about it months ago as his flash tuner ran into the same pproblems.

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    laloosh, please don't mention that douche in this thread...i'd really hate to see another useful thread go to junk with his useless/senseless marketing and have 100 pages of bs...let's just try to stay on topic so we don't take time away from his single turbo work as he's already fairly late on that

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    guys your doing alot of homework. hit up hpf on the phone and tell them what you'd like to see happen on the tuning end.
    im sure @dzenno could do some convincing.

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    You are right sticky can you delete my post as ten minutes passed.

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    stupid safari...double post sorry

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    All this hubbub is a little goofy in my opinion. Really just shows there could be a lot more to overcome in having full control. They haven’t even touched the BMW fuel tables yet, apart from altering AFR.

    Single turbo would take huge efforts in remapping, overcoming 2 fuel banks, WG control, etc. Not going to happen with a flash anytime soon.

    This post is pertaining to Cobb limits, NOT fuel limits. Which is overall very good for the community, but shouldn’t be misunderstood.

    Thanks for keeping us informed DZ!

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    http://www.e90post.com/forums/showthread.php?t=475789

    Figured this old thread I created deserves a blast from the past.

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    Click here to enlarge

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    Click here to enlarge Originally Posted by JoshBoody Click here to enlarge
    All this hubbub is a little goofy in my opinion. Really just shows there could be a lot more to overcome in having full control. They haven’t even touched the BMW fuel tables yet, apart from altering AFR.

    Single turbo would take huge efforts in remapping, overcoming 2 fuel banks, WG control, etc. Not going to happen with a flash anytime soon.

    This post is pertaining to Cobb limits, NOT fuel limits. Which is overall very good for the community, but shouldn’t be misunderstood.

    Thanks for keeping us informed DZ!
    What do you mean they haven't even touched the BMW fuel tables yet? They definitely have and do modify them...i'm not sure how you'd know the effort involved in tuning a single turbo when no one but cobb and possibly some flash tuners have yet seen what's available in the DME...let's not do this to this thread please unless you must...

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    Click here to enlarge Originally Posted by dzenno Click here to enlarge
    What do you mean they haven't even touched the BMW fuel tables yet? They definitely have and do modify them...i'm not sure how you'd know the effort involved in tuning a single turbo when no one but cobb and possibly some flash tuners have yet seen what's available in the DME...let's not do this to this thread please unless you must...
    Sorry no single talk, to expand on Cobb and fueling:
    All Cobb has done with fueling is revise the AFR table and the DME adjusts IPW mainly… based on stock BMW tables. You can see this when hitting higher boost, which I understand is rescaled so the load value shows lower than actual. This will result in STFT trims rising when these load limits are reached. In your case with RBs your load is already higher at each boost level, so across the board I would expect higher trims then others… CL making up the difference in mapping. I’m sure there’s no issue yet, but run a race gas map with no meth and you may start to see some limitations. Anyway mostly just speculation on my part. I’m sure with RBs, Cobb is probably beginning to experiment with more fueling alterations.

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    Excellent Dzenno, your work is a HUGE contribution to the community Click here to enlarge

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    Click here to enlarge Originally Posted by JoshBoody Click here to enlarge
    Sorry no single talk, to expand on Cobb and fueling:
    All Cobb has done with fueling is revise the AFR table and the DME adjusts IPW mainly… based on stock BMW tables. You can see this when hitting higher boost, which I understand is rescaled so the load value shows lower than actual. This will result in STFT trims rising when these load limits are reached. In your case with RBs your load is already higher at each boost level, so across the board I would expect higher trims then others… CL making up the difference in mapping. I’m sure there’s no issue yet, but run a race gas map with no meth and you may start to see some limitations. Anyway mostly just speculation on my part. I’m sure with RBs, Cobb is probably beginning to experiment with more fueling alterations.
    This map will run without issues on race gas and NO meth. I'm personally only using meth to raise octane and be safe. I'm not sure how you can say in one post that cobb doesn't touch bmw tables and then in this post contradict and say they do revise the AFR table. Is AFR table not a table? Click here to enlarge Alas...

    I think, and obviously this is a guess as only Cobb would know at this point, the way to adjust fueling on this DME is to program AFR targets for load and let the DME worry about fuel pressure and IPWs. Why would you need to touch anything IPW related if we can assume that the DME has full control over it and will do calculations based on load to hit the desired AFR target...if you were to go with aftermarket fuel injectors or any component of the fuel system then I do see that being a potential thing to work out but given the fuel system is 100% stock the DME should be able to calculate the appropriate parameters to meet various targets under load and properly fuel this engine without unnecessarily large fuel pressures, in other words, using the most optimum configuration for a given target/load...

    thanks for dropping the speculations on single turbo tuning as i have just as many even more legitimate ones when a piggyback is used...

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