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Thread: Fuel pressure question? AFPR, with Walbro 255 pump, TBI 60 pound injectors.

  1. #1
    EFI tuning addict 96lt4c4's Avatar
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    Fuel pressure question? AFPR, with Walbro 255 pump, TBI 60 pound injectors.

    I am working on my 94 Blazer and I am going to change things up a bit. The truck has a 383 in it with a very mild cam, World Product SR Tourqer heads, running the stock intake ported and 2" TBI bores. The TBI has 2" bores with all the spacers...etc running 454 injectors (80 pound per hour). The pump in there now is a GM later model truck pump for a Vortec. I have the tank out and I am going to swap in a Walbro 255 pump, pull the injector pod off and mod the FPR to make it adjustable, also going to stick the stock 350 (55 pound per hour) injectors back in. It seems like I have fought the tune on this truck since day one. Mainly cold idle, winter time, runs really rich. My question is what would be a good starting point to set my fuel pressure to with this setup. After its set I will leave it alone and work on the tune.
    Last edited by 96lt4c4; 07-06-2012 at 02:43 PM.

    -1999 Hugger Orange SS, LS2 402 T56, 9 inch Ford 3.90 gears, Tuned with HP Tuners
    -2002 Cavalier, Tuned with HP Tuners
    -1994 Full Size Blazer ,383 TBI 4L60E, 4.10's, Tuned with Tunerpro RT (Where it all began)

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    EFI tuning addict 96lt4c4's Avatar
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    Guess I should have looked at the FAQ at the top of the page. I am going to guess and say I have at least 300 hp, so it looks like I need about 16 pounds of fuel pressure. We shall see what happens.

    -1999 Hugger Orange SS, LS2 402 T56, 9 inch Ford 3.90 gears, Tuned with HP Tuners
    -2002 Cavalier, Tuned with HP Tuners
    -1994 Full Size Blazer ,383 TBI 4L60E, 4.10's, Tuned with Tunerpro RT (Where it all began)

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    Fuel Injected! jameslleary's Avatar
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    Ooofff....60 PSI on 80lb injectors. Yikes. The 94-95 TBI 454 was the only one to use a high pressure pump, regulated to 30psi, but it used 40pph(@13psi) injectors, which ended up being 75pph, with the higher pressure.
    What supply pressure are those 80pph injectors rated?

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    RIP EagleMark's Avatar
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    Quote Originally Posted by 96lt4c4 View Post
    Guess I should have looked at the FAQ at the top of the page. I am going to guess and say I have at least 300 hp, so it looks like I need about 16 pounds of fuel pressure. We shall see what happens.
    Did you find the Injector Sizing Spreadsheet? You can enter fuel pressure, injector size engine displacement and see if it will support estimated HP. One big thing to factor in and included in spreadsheet is BPW to all this or your screwed...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

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    EFI tuning addict 96lt4c4's Avatar
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    Quote Originally Posted by jameslleary View Post
    Ooofff....60 PSI on 80lb injectors. Yikes. The 94-95 TBI 454 was the only one to use a high pressure pump, regulated to 30psi, but it used 40pph(@13psi) injectors, which ended up being 75pph, with the higher pressure.
    What supply pressure are those 80pph injectors rated?
    Sorry, I meant 60 pound per hour injectors, not 60 pounds of fuel pressure. I am running stock 13 psi fuel pressure with 80 PPH injectors right now. I am going back to the 55's and raising the fuel pressure.

    -1999 Hugger Orange SS, LS2 402 T56, 9 inch Ford 3.90 gears, Tuned with HP Tuners
    -2002 Cavalier, Tuned with HP Tuners
    -1994 Full Size Blazer ,383 TBI 4L60E, 4.10's, Tuned with Tunerpro RT (Where it all began)

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    EFI tuning addict 96lt4c4's Avatar
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    Quote Originally Posted by EagleMark View Post
    Did you find the Injector Sizing Spreadsheet? You can enter fuel pressure, injector size engine displacement and see if it will support estimated HP. One big thing to factor in and included in spreadsheet is BPW to all this or your screwed...
    Yes I found the spread sheet, thanks. I will take a look at the Base Pulse Width.

    -1999 Hugger Orange SS, LS2 402 T56, 9 inch Ford 3.90 gears, Tuned with HP Tuners
    -2002 Cavalier, Tuned with HP Tuners
    -1994 Full Size Blazer ,383 TBI 4L60E, 4.10's, Tuned with Tunerpro RT (Where it all began)

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    EFI tuning addict 96lt4c4's Avatar
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    Quote Originally Posted by EagleMark View Post
    Did you find the Injector Sizing Spreadsheet? You can enter fuel pressure, injector size engine displacement and see if it will support estimated HP. One big thing to factor in and included in spreadsheet is BPW to all this or your screwed...
    Which spreadsheet calculates base pulse width? I must have downloaded the wrong one?

    Nevermind, downloaded them all and found it, man this site is sweet...like a kid in a candy store...LOL
    Last edited by 96lt4c4; 07-06-2012 at 03:25 PM.

    -1999 Hugger Orange SS, LS2 402 T56, 9 inch Ford 3.90 gears, Tuned with HP Tuners
    -2002 Cavalier, Tuned with HP Tuners
    -1994 Full Size Blazer ,383 TBI 4L60E, 4.10's, Tuned with Tunerpro RT (Where it all began)

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    EFI tuning addict 96lt4c4's Avatar
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    I do have another question though, why is it the stock tune shows the injectors as 60 PPH and they are known as 55 PPH? I always called them 60's because thats what the stock tune shows.

    I just recalculated using one of the other sheets and it shows I need to run the 60's at 25 psi.
    Last edited by 96lt4c4; 07-06-2012 at 03:35 PM.

    -1999 Hugger Orange SS, LS2 402 T56, 9 inch Ford 3.90 gears, Tuned with HP Tuners
    -2002 Cavalier, Tuned with HP Tuners
    -1994 Full Size Blazer ,383 TBI 4L60E, 4.10's, Tuned with Tunerpro RT (Where it all began)

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    RIP EagleMark's Avatar
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    Once an internet rumor is started it can never be taken back!

    Your 55PPH and 60 PPH are 61PPH...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

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    RIP EagleMark's Avatar
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    I just recalculated using one of the other sheets and it shows I need to run the 60's at 25 psi.
    I was waiting for that!

    This also brings on many more tuning issues as the pressure is way outside of what the injector was designed for, can be done but way to much work.

    But your 80PPH injectors, at 85% Duty Cycle and .5 BSFC and 17 PSI (more realistic) will support 311 HP, now the key to get a good tune with this spreadsheet is the BPW is 102. Or at 16 PSI = 302 HP and BPW 105.5. I er to a little bigger, easy to take away fuel in tune, hard to add if it was never there... VE numbers can come down but can only go to 100 and should really never pass 95, but having WOT only need 85 is sweet....

    This is really KEY to tuning a modified engine with old 160 Baud ECM.

    Now you probably have a newer 16197427 and it can be fudged a little after this calculation by changing injector size, smaller = more fuel and larger = less fuel, but you still need enough fuel to feed the beast at WOT or all your idle and drive ability tuning has been a waste of time. This fudging will only work so far and you'll be able to tune in low end or high end, usually you end up short at high end and injector duty cycle goes 100% or static... so only fudge a little after calibration.

    I like to calibrate a tune correctly to start. If it does not have enough fuel to support WOT High RPM, then why start?

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  11. #11
    EFI tuning addict 96lt4c4's Avatar
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    Quote Originally Posted by EagleMark View Post
    I was waiting for that!

    This also brings on many more tuning issues as the pressure is way outside of what the injector was designed for, can be done but way to much work.

    But your 80PPH injectors, at 85% Duty Cycle and .5 BSFC and 17 PSI (more realistic) will support 311 HP, now the key to get a good tune with this spreadsheet is the BPW is 102. Or at 16 PSI = 302 HP and BPW 105.5. I er to a little bigger, easy to take away fuel in tune, hard to add if it was never there... VE numbers can come down but can only go to 100 and should really never pass 95, but having WOT only need 85 is sweet....

    This is really KEY to tuning a modified engine with old 160 Baud ECM.

    Now you probably have a newer 16197427 and it can be fudged a little after this calculation by changing injector size, smaller = more fuel and larger = less fuel, but you still need enough fuel to feed the beast at WOT or all your idle and drive ability tuning has been a waste of time. This fudging will only work so far and you'll be able to tune in low end or high end, usually you end up short at high end and injector duty cycle goes 100% or static... so only fudge a little after calibration.

    I like to calibrate a tune correctly to start. If it does not have enough fuel to support WOT High RPM, then why start?
    Yes, its a 94 Truck so it has the 7427 in it. I have done what you are talking about, fudging the the injector constant while datalogging, and emulating. I watch the BLMs and fudge the consant to get it close in real time. Seems to work OK most of the time. So it looks like I may be keeping the 80;s in there and just doing some more tuning.

    -1999 Hugger Orange SS, LS2 402 T56, 9 inch Ford 3.90 gears, Tuned with HP Tuners
    -2002 Cavalier, Tuned with HP Tuners
    -1994 Full Size Blazer ,383 TBI 4L60E, 4.10's, Tuned with Tunerpro RT (Where it all began)

  12. #12
    RIP EagleMark's Avatar
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    If you get the injector size correct then no BPW in that PCM... so it's a matter of building a smooth VE table to work with. Like 85 at WOT stuff down to little lower then stock at idle area with cam.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

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    Fuel Injected! pmkls1's Avatar
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    You need to be careful with the 255lph walbro pump. I have been running a walbro high volume AND high pressure pump ( there are 2 255lph pumps available, a standard pressure and a high pressure) on my '89 Firebird Formula for ~3 years now and have had to deal with excessive fuel pressure ever since. The car was originally running the stock 5.0l L03 TBI and 1228746 ECM, but is now running an L31 5.7 and 16197427 PCM. All the while, I have been running the stock 305 injectors and an O.E. style billet aluminum adjustable FPR with an added vacuum reference port. With the original regulator modified to be adjustable and the spring tension backed off as far as possible, the fuel pressure was still running in the mid-20's due to the flow of the pump exceeding the demands of the injectors and the capacity of the return passages in the throttle body. I then installed the billet FPR and set a base pressure of 30psi and when referenced to intake vacuum it would drop to ~21psi at idle. Even with the 350, the fuel demands aren't enough to allow for a lower fuel pressure. I know that your engine will definitely have a higher fuel demand, but it probably won't be significant at idle. I don't have any known tuning issues with that fuel pressure, but it can cause problems and most guys on here don't recommend more than 21psi on TBI injectors.

    Now, you do have options that would allow for use of this pump with your current configuration and also have lots of room for any future upgrades. You can always use a block off plate in place of the stock regulator and use an external regulator that will allow for the use of just about any injection & fuel pump combo. I would have done this myself a long time ago, but there's always something more important I need to buy. I'm a little surprised that you haven't had any issues with a vortec application fuel pump, but I don't know the flow rating of them either. Anyhow, I just wanted to give you a heads up before you install the walbro. There's nothing wrong with them, they just put out a little more than a typical TBI system can handle without some accompanying mods/hardware.

  14. #14
    EFI tuning addict 96lt4c4's Avatar
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    Quote Originally Posted by pmkls1 View Post
    You need to be careful with the 255lph walbro pump. I have been running a walbro high volume AND high pressure pump ( there are 2 255lph pumps available, a standard pressure and a high pressure) on my '89 Firebird Formula for ~3 years now and have had to deal with excessive fuel pressure ever since. The car was originally running the stock 5.0l L03 TBI and 1228746 ECM, but is now running an L31 5.7 and 16197427 PCM. All the while, I have been running the stock 305 injectors and an O.E. style billet aluminum adjustable FPR with an added vacuum reference port. With the original regulator modified to be adjustable and the spring tension backed off as far as possible, the fuel pressure was still running in the mid-20's due to the flow of the pump exceeding the demands of the injectors and the capacity of the return passages in the throttle body. I then installed the billet FPR and set a base pressure of 30psi and when referenced to intake vacuum it would drop to ~21psi at idle. Even with the 350, the fuel demands aren't enough to allow for a lower fuel pressure. I know that your engine will definitely have a higher fuel demand, but it probably won't be significant at idle. I don't have any known tuning issues with that fuel pressure, but it can cause problems and most guys on here don't recommend more than 21psi on TBI injectors.

    Now, you do have options that would allow for use of this pump with your current configuration and also have lots of room for any future upgrades. You can always use a block off plate in place of the stock regulator and use an external regulator that will allow for the use of just about any injection & fuel pump combo. I would have done this myself a long time ago, but there's always something more important I need to buy. I'm a little surprised that you haven't had any issues with a vortec application fuel pump, but I don't know the flow rating of them either. Anyhow, I just wanted to give you a heads up before you install the walbro. There's nothing wrong with them, they just put out a little more than a typical TBI system can handle without some accompanying mods/hardware.
    Well that stinks, I just got the pump too. I guess I will stick it in and see why happens. I have AN style lines going from the filter under the truck to the TBI and back so if I have to add a regulator its no big deal.
    Last edited by 96lt4c4; 07-08-2012 at 12:51 AM.

    -1999 Hugger Orange SS, LS2 402 T56, 9 inch Ford 3.90 gears, Tuned with HP Tuners
    -2002 Cavalier, Tuned with HP Tuners
    -1994 Full Size Blazer ,383 TBI 4L60E, 4.10's, Tuned with Tunerpro RT (Where it all began)

  15. #15
    EFI tuning addict 96lt4c4's Avatar
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    I was just looking throught the stock tune and tell me if am wrong but is the stock BPW 397.6? So it needs to go down almost 200 usec?

    Last edited by 96lt4c4; 07-08-2012 at 03:44 PM.

    -1999 Hugger Orange SS, LS2 402 T56, 9 inch Ford 3.90 gears, Tuned with HP Tuners
    -2002 Cavalier, Tuned with HP Tuners
    -1994 Full Size Blazer ,383 TBI 4L60E, 4.10's, Tuned with Tunerpro RT (Where it all began)

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