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Thread: fpcm tuning

  1. #1
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    fpcm tuning

    Anyone have and advice on how to tune a fpcm? I have a DSX aux pump and I'm told to take full advantage you need to tune the fpcm. Anyone have an example or the time to explain the basics?

  2. #2

  3. #3
    I looked into this awhile back. I had to use credits to get ability to look at it. it has pressure versus battery voltage. this is from a Silverado. not sure if this will help but at least you can take a look.
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  4. #4
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    if you want to understand why you change things rather than just copy, here a link from DSX :https://dsxtuning.com/blogs/dsx-tech...ntrol-strategy

  5. #5
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    Quote Originally Posted by JASON11WS6 View Post
    Anyone have and advice on how to tune a fpcm? I have a DSX aux pump and I'm told to take full advantage you need to tune the fpcm. Anyone have an example or the time to explain the basics?
    Don’t have an aux pump, never tuned for one, but what I get from the DSX article is maybe you set the High Flow at a lower pressure than at Normal flow, and put it to go into high flow at as close as possible to the activation point of the aux pump. This would cause the FSCM to start ramping down the stock pump as the aux pump kicks in. Then you can make adjustments to the transition rate in the High Flow area to make larger or smaller steps in pressure as needed to fine tune it. But take this with a pound of salt as I’m “NotSure”.

  6. #6
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    I just did this in my CTS V. All numbers are assumed to be for the CTS V, however it should correlate easily.

    First, you need to log fuel flow rate, fuel pump duty cycle (make sure it is through the FPCM, *not* the ECU), and fuel pressure in your logs. Fuel flow rate is honestly the most important, as it determines what mode you will be in.

    You'll find that there are likely several modes correlating to fuel pressure: Low Flow, Normal, High Flow, and default.
    You'll also be able to potentially increase fuel pump output by marginally increasing the Fuel Pump duty cycle tables, but this is a grey area and may not be necessary.

    However the most important part is to verify what mode your pumps are alternating in: What's happening is that for most of us on pump gas, our fuel flow rate is so low under normal driving, that we are typically in "Low Flow" mode in the tune (In my CTSV, this commands 50psi). Most bolt-on cars will use enough fuel that when you mash it, your flow rate jumps so much that you simultaneously clear the "low flow" mode threshold, bypassing the normal FP mode (60psi) altogether and going straight into high flow mode (70 psi); so it looks like in stock form our commanded fuel pressures jump from 50 to 70 psi.

    Only after altering my "high flow" upper range did this manifest into that "fuel pressure dip" I see when on Ethanol, is actually my being in the "Normal" mode due to the vastly altered fuel flow requirements - and Normal mode allows for fuel pump modulation(!). Ironically, that means in Normal mode, the FPCM is reducing pump duty cycle to match a lower commanded rail pressure and giving us "the dip" in our WOT pulls.

    High Flow mode commands 100% pump duty cycle regardless of commanded rail pressure, so you need to LOWER your "High Flow Upper" values enough to where you trigger it when mashing the pedal for WOT at a given RPM. Simply put, start in a low RPM that's realistic (ie 3k RPM), mash the pedal and data log. Find what your fuel flow is at the beginning of your run in lb-hr, then change the High Flow Upper table to be slightly less than that across the board. Make sure your High Flow Lower table is of course less than that value, as that will turn off High Flow mode when you get out of WOT.

    You may have to modulate WHEN you commend High Flow Mode if you are getting crazy high rail pressures - there is a balancing act between having enough rail pressure and blowing gaskets! This is where some common sense, small changes and a good data log can help you. For most GenIV cars, your pressure relief valve is anywhere from 68-72psi, so don't try to command 80psi. Find "The dip" in your log and command High Flow Mode beginning at the RPM it happens, and you should be GTG!


    high-flow-and-low-flow-settings-jpg.151016.jpg

    If you are running out of fuel pressure at the end of your run, then increasing fuel pump duty cycles at the appropriate voltage range (13.5-15 v) can further increase output slightly. I would make small % changes here and monitor for progress.

    I have aftermarket in-tank pumps along with my Dsteck Aux kit. I increased the fuel pump duty cycle in relevant areas (fuel flow vs voltage) by ~5% and slightly adjusted the Open Loop DC modifier to get closer to "1.000" at 15 volts, which is where my system voltage hangs out. This table may reflect limitations to the factory pump flow rates versus aftermarket pumps like the DW300, so I'd suggest small changes and monitor for progress. But I suspect aftermarket pumps could see some real benefit here.

    fuel-pump-dc-jpg.151052.jpg
    Last edited by Random84; 05-17-2021 at 11:27 AM.

  7. #7
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    Random84 Quick ? if you don't mind me jumping in on this thread. I have a 2012 Cts-V and installed DW300C pumps and FPR and now it keeps throwing code P0231 Fuel Pump Secondary circuit low is this something i can get tuned out or am i going to need an Aux Pump? Thank you in advance for any info.

  8. #8
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    Per my PM: Yes, go to the FPCM tab in "fuel" in HP Tuners. Go to the DTC tab on that page. Scroll down to P0231, and select "no error reported." You may have to pay extra to access the FPCM portion of the tune, but you have to disable the code on the FPCM specifically.

  9. #9
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    I am trying to understand what parameters need to be adjusted to gain control of the aux DW300 pump. I installed the dual DW300 kit with the updated higher pressure regulator. The fuel pressure spikes at 5100 rpm (see attached log file) and my AFR dips as a result. I was able to shift the point at which the pressure spikes by adjusting the high flow upper table, but I have hit a threshold where I cant seem to shift / smooth it at > 5100 rpm. I have attached a log and tune file for reference. Any help / pointers would be greatly appreciated.cruise5_Mods3.hplZW_2011_CTSV_Mods_5_Flex.hptZW_2011_CTSV_Mods_5_Flex.hptcruise5_Mods3.hplZW_2011_CTSV_Mods_5_Flex.hptcruise5_Mods3.hpl

  10. #10
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    CCTBSS, are you using the FSCM? I don't see fuel pump duty cycle or desired fuel pressure in the log. The Low/Normal/High mode condition settings seem odd, 3 different steps on the high flow upper. How are the pumps wired?

  11. #11
    Senior Tuner Lakegoat's Avatar
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    On my '14 Silverado, under fuel system--I don't have a tab for FSCM. It shows FSCM fitted and has all of the pressure settings, but not the open loop tabs. It has a ZL1 in tank pump and 30% fuel lobe. Is this just an earlier OS that doesn't have access? Nothing that I click on asks for credits to access the info. Thanks
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    2005 GTO, TrickFlow 225, Magnuson 2300, 4L80, 4 link 8.8
    2013 Silverado 5.3, 6L80

  12. #12
    FSCM Tab.pngOL Fuel Tab.png

    Lake, your OL fuel is under Engine > Fuel > Open Loop/Base

    Your FSCM is under "Fuel Sys" up top where you choose Engine, Trans, System, Speedo