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Thread: How to tune for return fuel system.

  1. #1
    Advanced Tuner SJSchafer's Avatar
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    Thumbs up How to tune for return fuel system.

    Okay, now for part 2 of our injector tuning how-to. This one involves tuning for a return style conversion. I am not going to go into detail about the install itself, as that is already covered in other threads. This is strictly meant to address the changes that need to be made to tune for them.

    By far, the easiest way to go about this is to first make sure you have good injector tables to start with. It is much easier to make the proper changes to tables that are correct to begin with. If you need help with that part of it, there is a how-to here: http://www.hptuners.com/forum/showthread.php?t=17962

    So the first step is to decide what you want your base pressure to be. That is the rail pressure with the car running and the vacuum line to the regulator disconnected. By messing with the LSJ injector spreadsheet, I found that my injectors have a static flow of 63.5lbs.hr at a rail pressure of 42psi. I decided to go with that (since that is the highest our ECM supports without using a modifier) and set my regulator at 42psi base pressure. Since I now have a return system with a regulator that references manifold vacuum, the effective pressure will be the same across the board. That means my IFR table will be set at 63.5 across the table like this:



    Now set your modifier vs volts to 1 across the board.



    Next I need to do some math. My offset table is correct for a fuel pressure of 58psi, with an effective pressure that goes up when the car is in vac and goes down when it is in boost like our cars do stock. Since our cars don’t do that anymore, we need to change this table. Since I set my regulator at 42psi and my offset table is for 58 psi, I subtract and come up with 16. I next go to the converter in HPTuners and convert that to kPa.



    So I am running a base pressure that is about 110kPa less than stock. Remember that vacuum raises effective pressure and boost lowers it. I go to my offset vs volts vs vac table. I need to effectively lower my pressure by 110kPa. I choose the -108kPa vac column and I copy



    And paste to all of the columns, so that they are the same all the way across.



    Keep in mind that I decided to go with a fairly low base pressure, so that I could stay within the limits of my IFR table and to give myself a higher pulsewidth at idle, making it much much easier to tune these things. If you decide to run a higher pressure that puts you above 63.5lbs/hr you will need to use a modifier above "1" to get the correct IFR.

    That’s it! Now go tune your MAF and adders…
    '07 Cobalt SS/SC
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  2. #2
    Advanced Tuner black06g85's Avatar
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    good info man, I'll be using this same general setup when I finally do my fuel system over, seems to be holding up ok right now with just the bigger pump. It's going to be fun trying to tune in the 79lb'ers like this though lol.
    2006 cobalt (no more turbo)
    m62 2.7 pulley, E85, 79lb/hr injectors, 4-2-1 longtube header, airbox mod, stock catback

    1998 Trans am 5.3 iron block 317 heads 88mm turbo e85 105lb/hr injectors, twin 255's.... build in progress

    2014 wrx mild tune 18psi pump gas

  3. #3
    Advanced Tuner black06g85's Avatar
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    btw ltft are almost at 0 give or take +/-.5 can't believe that.
    2006 cobalt (no more turbo)
    m62 2.7 pulley, E85, 79lb/hr injectors, 4-2-1 longtube header, airbox mod, stock catback

    1998 Trans am 5.3 iron block 317 heads 88mm turbo e85 105lb/hr injectors, twin 255's.... build in progress

    2014 wrx mild tune 18psi pump gas

  4. #4
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    Quote Originally Posted by SJSchafer
    Okay, now for part 2 of our injector tuning how-to. This one involves tuning for a return style conversion. I am not going to go into detail about the install itself, as that is already covered in other threads. This is strictly meant to address the changes that need to be made to tune for them.

    By far, the easiest way to go about this is to first make sure you have good injector tables to start with. It is much easier to make the proper changes to tables that are correct to begin with. If you need help with that part of it, there is a how-to here: http://www.hptuners.com/forum/showthread.php?t=17962

    So the first step is to decide what you want your base pressure to be. That is the rail pressure with the car running and the vacuum line to the regulator disconnected. By messing with the LSJ injector spreadsheet, I found that my injectors have a static flow of 63.5lbs.hr at a rail pressure of 42psi. I decided to go with that (since that is the highest our ECM supports without using a modifier) and set my regulator at 42psi base pressure. Since I now have a return system with a regulator that references manifold vacuum, the effective pressure will be the same across the board. That means my IFR table will be set at 63.5 across the table like this:



    Now set your modifier vs volts to 1 across the board.



    Next I need to do some math. My offset table is correct for a fuel pressure of 58psi, with an effective pressure that goes up when the car is in vac and goes down when it is in boost like our cars do stock. Since our cars don’t do that anymore, we need to change this table. Since I set my regulator at 42psi and my offset table is for 58 psi, I subtract and come up with 16. I next go to the converter in HPTuners and convert that to kPa.



    So I am running a base pressure that is about 110kPa less than stock. Remember that vacuum raises effective pressure and boost lowers it. I go to my offset vs volts vs vac table. I need to effectively lower my pressure by 110kPa. I choose the -108kPa vac column and I copy



    And paste to all of the columns, so that they are the same all the way across.



    Keep in mind that I decided to go with a fairly low base pressure, so that I could stay within the limits of my IFR table and to give myself a higher pulsewidth at idle, making it much much easier to tune these things. If you decide to run a higher pressure that puts you above 63.5lbs/hr you will need to use a modifier above "1" to get the correct IFR.

    That’s it! Now go tune your MAF and adders…
    That is good info, I just have a problem with setting your Injector flow rate modifier VS Batt voltage to 1 across the board.

    This is a pulse width adder for Bat Volts only, and should not affect your tune as long as the battery voltage remains at 14.5 volts, but if it drops you could go lean due to load from fans, AC lights etc.

    Ted.

  5. #5
    Setting it to 1 is neccessary because this map was to based on the effects of B+ (and resulting injector current slope) against the injector delivery slope FOR THE STOCK INJECTORS. (the 60# will be dramatically different) But by eliminating this variable you will be able to create more fuel delivery stability elsewhere.

    This is especially important if you are using a BOOST-A-PUMP amplifier as the pump is essentially unaffected by sag-out in B+
    HTH
    WopOnTour
    Last edited by WopOnTour; 05-19-2008 at 02:10 PM.

  6. #6
    Advanced Tuner SJSchafer's Avatar
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    Quote Originally Posted by JANNETTYRACING
    That is good info, I just have a problem with setting your Injector flow rate modifier VS Batt voltage to 1 across the board.

    This is a pulse width adder for Bat Volts only, and should not affect your tune as long as the battery voltage remains at 14.5 volts, but if it drops you could go lean due to load from fans, AC lights etc.

    Ted.
    Actually, setting the modifier vs volts back to 1 would be putting it back to its stock configuration. You are correct that the injectors do fire differently in lower voltage situations as they do in higher voltage situations. That is why the offset table varies by voltage. The modifier table actually multiplies the values of the IFR tables and lets you set different values for drops in voltage. The 13v table affects 13v and up. These are not needed as long as you're not exceeding your IFR table limit and your offsets are correct.
    '07 Cobalt SS/SC
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    Questions about 60s? <-- click!
    How to tune for return fuel system <--click

  7. #7
    Quote Originally Posted by SJSchafer
    Actually, setting the modifier vs volts back to 1 would be putting it back to its stock configuration. You are correct that the injectors do fire differently in lower voltage situations as they do in higher voltage situations. That is why the offset table varies by voltage. The modifier table actually multiplies the values of the IFR tables and lets you set different values for drops in voltage. The 13v table affects 13v and up. These are not needed as long as you're not exceeding your IFR table limit and your offsets are correct.
    That's exactly why we completely rewire the pump (eliminating the fuse block and stock relay) with 12AWG minimum (dependin on BAP model used) and add a voltage amplifier (KenneBell Boost-A-Pump) in all the LSJ cars I work with.
    Nice write-ups BTW!
    WOT

  8. #8
    Advanced Tuner SJSchafer's Avatar
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    Quote Originally Posted by WopOnTour
    That's exactly why we completely rewire the pump (eliminating the fuse block and stock relay) with 12AWG minimum (dependin on BAP model used) and add a voltage amplifier (KenneBell Boost-A-Pump) in all the LSJ cars I work with.
    Nice write-ups BTW!
    WOT
    Thanks WOP.
    '07 Cobalt SS/SC
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    Questions about 60s? <-- click!
    How to tune for return fuel system <--click

  9. #9
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    I agree with that especially since I didn't see it was a multiplier and not the actual Batt comp table.

    Ted.

  10. #10
    Senior Tuner Ben Charles's Avatar
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    Im new at this and sent a PM to the original poster, but why was the -108 column used?? Also why was it copied and pasted in all other columns??

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  11. #11
    Advanced Tuner SJSchafer's Avatar
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    Quote Originally Posted by Ben Charles View Post
    Im new at this and sent a PM to the original poster, but why was the -108 column used?? Also why was it copied and pasted in all other columns??
    Answer to the first question, "So I am running a base pressure that is about 110kPa less than stock. Remember that vacuum raises effective pressure and boost lowers it. I go to my offset vs volts vs vac table. I need to effectively lower my pressure by 110kPa."

    In answer to your second question, with a return style system the fuel pressure changes with vac/boost. In other words, "Since I now have a return system with a regulator that references manifold vacuum, the effective pressure will be the same across the board." Since the effective pressure is the same across the board, the offsets do not change with boost/vac, only with voltage.
    '07 Cobalt SS/SC
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    Questions about 60s? <-- click!
    How to tune for return fuel system <--click

  12. #12
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    How wil that translate to a 05 gto e40 ecm were you don't have the boosted areas in youe tables and do u still scale the injectors and other areas

  13. #13
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    So I'm in the process of installing a return style system on my cobalt all for all the obvious reasons but mostly to get a better idle and get rid of a strange P0172 I get when decelerating. But there is still some things that I don't understand.

    1) I see you modify the Offsets vs Volts vs VAC table but you don't change anything from the vs MAP table. Why ? Shouldn't the offsets be the same also in the MAP table ?

    2) There is an option to select MAP or VAC tables. Will the ECU use only VAC if I select VAC or is it going to go to MAP automatically when in boost ? Because the maximum value from the VAC table is 11 PSI. This would mean that you can't boost over 11 PSI without the risk of going lean (that is if you are using the stock returnless fuel rail). On the other hand if you remove atmospheric pressure from MAP values you get a maximum pressure of 14.3 PSI. So I guess choosing MAP table would give 3.3 PSI more boost pressure before the car starts going lean ? (Of course using a boost referenced regulator would make it possible to go way over that limitation)

    So if I understand well, after 11 PSI from the VAC table, the ECU will command the Offsets from the last column ? Since the values are the same across the board now, this would have no effect on a boost referenced regulator. That would make modifying and using the MAP table useless. Would it ?

  14. #14
    Senior Tuner cobaltssoverbooster's Avatar
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    It's kpa vacuum boost refrence is like 27 psi on that axis. Whatever you set the map vac selector to that's the table it runs. That's why we only change 1 table of offsets.

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    Good.

  16. #16
    Senior Tuner cobaltssoverbooster's Avatar
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    i miss spoke in my last post.
    -120 kpa vac is roughly 17.4 psi boost and 80 kpa vac is roughly 11.6 psi vacuum. 11.6 psi vacuum is about -23.6 inHg.

    conversion formula is from fluid dynamics and differential pressure studies.

    anyways unless you can get the SD flow values in the factory layout for GM which some members here can, i would recommend researching other injectors. between the spray pattern and low pulse characteristics alone there are a few better options that flow the 60-70 lbhr that your looking for. if you already purchased these SD 60's listen to DSteck wisdom, research his injector posts, and then come here to see what we do differently. the lsj has internal table multipliers which is why your voltage offset data will not work correctly if you just convert it and enter it into the ecu. not to mention converting ford data into gm data is not a recommended way of accumulating data. yes, if you have the formula for conversion which is floating around here somewhere, it would be a good starting point. Nothing compares to having them flow benched to your specific parameters. a good flow testing facility will recognize your table axis requirements and acquire better test data by providing results that match your axis. (voltage, and rail pressures)
    good luck
    Last edited by cobaltssoverbooster; 02-08-2014 at 05:22 PM.
    2000 Ford Mustang - Top Sportsman

  17. #17
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    does this info apply to 80's as well?
    I have been trying to learn this stuff, and I've had some great help, but something in my tune's still not right. I suspect it's the injector tables, and that this thread may be some, or all, of the answer.

    is anybody willing to coach a noob through the process ? I'm afraid if I just follow this thread without the basic setup correct that it will cause even more issues, and quite frankly, I'm a little overwhelmed by the companion "how to set up 60's" thread

    my car -- 2007 LSJ, stock long block / stock M62 with 2.7 pulley / RAW 3" cai / LS4 tb / ported and single pass intake / ZZP lt header, catless dp, 3" tube / ZZP brfps / 80's & E85

    EDIT: so I went off after I posted and did some reading. I used the Omega spreadsheet for my injector tables, but I opened it tonight and noticed that it is set for 80lb @ 43.5----- ZZP advertises 89lb at 43.5 psi -----AND, neither the 80lb value or the 58psi value can be edited in the spreadsheet, SO--- right off the bat my values CAN'T be right !!!

    in addition, I have an Autometer fuel pressure gauge with the sending unit right in the end of the rail (OTTP adapter) and it reads 38psi at idle (BRFPS) 89lb @ 43.5psi = 83.18lb @ 38psi

    would it be correct then, to go -- 83.18 divided by 63.5 = 1.3099 --- enter the IFR vs. KPA value as 63.5 across the table, and the flow rate modifier as 1.3 or 1.31 across the table ?

    then I run into an issue at the next step -- my pressure difference -- 20 psi = 137.895kpa , is off the table -- so how do I calculate that data ? Or, am I forced then, to raise fuel pressure and change my modifier ?
    Last edited by wayfarer; 03-08-2014 at 12:12 AM.

  18. #18
    Senior Tuner cobaltssoverbooster's Avatar
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    this thread is for a return fuel system so the first question is did you install a fuel pressure regulator that has a return and boost port? if no then this thread will not help you any.

    the reason this thread is here is because in boosted applications with return systems, the fuel pressure regulator has a boost reference port that increases the rail pressure with boost(normally a 1:1 ratio) 1 psi boost will lift fuel pressure 1 psi keeping the pressure differential the same. this requires a complete overhaul of the fuel injector calibration. the max flow rate will become a constant rate since it is fixed to a specific fuel pressure 43.5 is normally the chosen route but not limited to other pressures of course.
    since boost reference keeps the pressure differential constant at all times, the offset multiplier will become fixed on the vac or map axis and the only factor effecting flow will become voltage as it changes the strength of the coil. low voltage makes it harder to open and high opens it easier so as you would guess less fuel at 10v than 14v with the same duty cycle rate.

    if you have a factory setup then you get to keep the changing pressure differential which causes a change in maximum flow rate per kpa, and of course a change in flow modifiers by voltage and vac or map whichever is selected. setting up for factory is 100% different than boost referenced returns.

    NOTE: Pressure regulators that have a return port are also available without boost reference ports. A non-boost referenced regulator will hold the rail pressure at a fixed psi like the stock system so in that case of a return system only will you need to keep the same style injector calibration as factory.

    please fill us in some more on your setup and we can help you get to where you need to be.
    which injectors? Simens Deka 80's, EV series in 80's calibration??
    what fuel pressure? stock, fixed non referenced, boost referenced??
    2000 Ford Mustang - Top Sportsman

  19. #19
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    yes, I have a boost referenced / return style system. Mine is a ZZP "BRFPS" (boost referenced fuel pressure system) with the regulator mounted underneath the car near the fuel tank. currently my Autometer fuel pressure gauge tells me that my idle fuel pressure is 38 psi.


    http://shop.zzperformance.com/store/...re-System.aspx

    the factory pressure regulator in the tank has had the ball and spring removed, so I am strictly boost referenced at this time.


    I have the Seimens /Mototron 80's from ZZP http://shop.zzperformance.com/store/...jectors-4.aspx

  20. #20
    Senior Tuner cobaltssoverbooster's Avatar
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    Cool then you got to the right spot.

    flow rate adjustment for rail pressure shift will make you 52 lb/hr with a 1.6 modifier. this would be a great value set to use since the flow rate is a whole number and the multiplier is an even 1.6.
    as for the voltage offsets you are best sending the injectors out to be batch tested to find their exact multiplier for the pressure you wish to run.

    but as posted you can get a very close batch of numbers by doing some simple math. Old Rail Pressure - New Rail Pressure = Conversion Value. 43.5 - 38 = 5.5 psi convert to kpa 37.92 kpa. because you lowered the pressure this will become a negative drop so -37.92 kpa (efficiency goes down with drop in rail pressure vs a vacuum). next find the closest cell on your offset/volts/vac table and copy all the cells straight down. (your column will be the -39 column) now that its on your clipboard select the top cell in the first column and select paste. do that until it looks exactly the same in each column.

    now your injectors are voltage offset matched to the new constant rail pressure requirement pretty closely. your max flow rate is set into constant mode as well. you will need to monitor the offset table to make sure you don't have any anomalies that need to be fixed.
    best way to do that is disable the maf completely and tune your base ve table. once its locked down multiply your ve by 10% and save it as a separate file. flash it in and watch the trims. if the trims respond as -10 then the ecu is removing 10% fuel you just forcefully added and the offset in that range is good. if the trims come back different then the voltage offsets need to be adjusted in that section. apply new changes to the offset until the trims achieve the -10 value and then upload them into the original tuned ve file. your offsets and ve should be set now. tuning maf afterwards is simple and matching it to the pe table is a breeze now that all your base data is set up.
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