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

  1. #46
    EFI tuning addict 96lt4c4's Avatar
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    For some reason my cell phone camera makes the car look red,
    http://www.youtube.com/watch?v=YZ6Mo...7&feature=plcp

    http://www.youtube.com/watch?v=Utb6w...5&feature=plcp

    cant find your thread

    -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)

  2. #47
    RIP EagleMark's Avatar
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    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
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  3. #48
    Fuel Injected! pmkls1's Avatar
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    I love the pics of the Blazer and the bedliner paint job. I've always wanted one of those, but they're hard to come by. I don't have the want or need for 4 doors so a Tahoe has never interested me. Glad to see that you found the issue in the diaphragm, but I don't think that my car has ever held residual pressure after being shut-off. I don't pay much attention either because I don't have any starting issues. I'm curious about the taller spring just because elevated pressure replacement springs are usually shorter, but have a much higher rate. As long as you've got a good running vehicle, I wouldn't concern myself with something that trivial. 14psi is excellent pressure for TBI injectors and as long as you have a good and consistent idle quality with the larger injectors at that pressure I'd say you've got no need to mess with anything. I figured that at least the higher pressure gauge was off a little as those gauges aren't going to be very accurate compared to a test gauge usually. The camaro is pretty sweet too I might add and I'd take one of those over a 5th gen any day of the week. It looks like you've got staggered wheels on it, though. Are those original or did you install those ? There were too many setups the last couple years of the 4th gen cars for me to remember all the specifics. I've got a similar set of wheels (17x9.5 front 17x11 rear) sitting in the shed because the chrome is bubbling and peeling badly and I haven't found an affordable DIY method to remove the chrome yet. I took them off of my 3rd gen firebird over a year ago and I'm dying to get them back on there. But now I've gone completely away from the topic though.

    Mark, I'll post a few things I've found to be common issues on them in your thread.

  4. #49
    EFI tuning addict 96lt4c4's Avatar
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    I was thinking the same thing about the spring, I wish I would have taken pics now but it was late last night. The longer spring was made of heavier gauge wire and was obviously stiffer. I thought about cutting it down to the length of the other one to make it stiffer like you said. Just like a car spring when you cut a coil off the spring gets stiffer. I left it alone. If I do mod the regulator I will snap a picture of both springs and regulator housings. As far as the fuel bleeding off, when my truck sits for a while which it has been doing a lot of here lately, it has to crank longer to start. The regulator spring keeps fuel pressure in the TB so that it starts quicker. The old one with the groove in it was letting it bleed off. Plus the pump has a check valve it so I know thats good now too.

    Yeah, we all got a little of topic but hey...it happens with true gear heads. The front wheels on the Camaro are the stock 17x8.5. After I lowered it the rear wheels looked bad tucked up under the quater panels so I bought the 2 rear 17x11's. They are aftermarket. I love thidgens too, my best friend growing up had a 89 Formula 350 WS6. I almost had the car a couple years ago but the engine was locked up. It was his first car, lots of memories in that car. Wish I would have went ahead and bought it.

    -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)

  5. #50
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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?
    So instead of starting a new thread I'm digging this one up because this is an issue I'm faced with at the moment. I have two sets of injectors (61&80pph) and need to decide which to use. Either set I'll need to run at higher than stock pressure and I will be sending the injectors off to be cleaned and flow rated as well as having witch hunter measure latency.
    My engine setup should hopefully be close to 400 hp and assuming 0.45 BSFC and at 85% DC I'd need to run the 61pph and 80pph injectors at 35 psi and 21 psi respectively to give the engine the required fuel. So larger injectors/lower pressure or smaller injectors/higher pressure? What are the pros and cons of each?

    I'm running a vortec EP281 pump so higher fuel pressure is not an issue with respect to fuel supply.

    Whatcha guys think?
    95 ecsb vortec 357 10.44:1 scr LT4 hot cam single plane TBI 7427 $0D

  6. #51
    RIP EagleMark's Avatar
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    Bigger injectors at lower pressure! Pro is they work fine at that pressure, Con at higher pressure is they open slow and casue issues, no need for latency on TBI injectors, just a service.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  7. #52
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    Quote Originally Posted by EagleMark View Post
    Bigger injectors at lower pressure! Pro is they work fine at that pressure, Con at higher pressure is they open slow and casue issues, no need for latency on TBI injectors, just a service.
    Sounds good, thanks for your input. You don't think it would be beneficial to have latency checked at the pressure the injectors would be operating at though?
    95 ecsb vortec 357 10.44:1 scr LT4 hot cam single plane TBI 7427 $0D

  8. #53
    Fuel Injected! gregs78cam's Avatar
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    The only drawback that I can think of with running so much fuel through only two injectors is the pulsewidth at idle, it may be difficult for the PCM to get it to idle as lean as it should. I have found that the smallest pulsewidth I can run is around 0.488msec, which barely gets it down to stoich at a warm idle.
    1978 Camaro Type LT, 383, Dual TBI, '7427, 4L80E
    1981 Camaro Z-28 Clone, T-Tops, 350/TH350
    1981 Camaro Berlinetta, V-6, 3spd
    1974 Chevy/GMC Truck, '90 TBI 350, '7427, TH350, NP203, 6" lift, 35s

  9. #54
    Fuel Injected! gregs78cam's Avatar
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    Quote Originally Posted by 907 Chevy View Post
    Sounds good, thanks for your input. You don't think it would be beneficial to have latency checked at the pressure the injectors would be operating at though?
    If it doesn't cost any more it wouldn't hurt to check the numbers against what is in the PCM.
    1978 Camaro Type LT, 383, Dual TBI, '7427, 4L80E
    1981 Camaro Z-28 Clone, T-Tops, 350/TH350
    1981 Camaro Berlinetta, V-6, 3spd
    1974 Chevy/GMC Truck, '90 TBI 350, '7427, TH350, NP203, 6" lift, 35s

  10. #55
    RIP EagleMark's Avatar
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    It's be cool to see how they stack up to factory specs too!

    But I don't think it's called latency is it? Voltage offset?
    In $42 it's "INJ - Injector Correction Multiplier"
    In $0D it's "Injector Offset vs. Battery Voltage"

    Or did I miss the boat?

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  11. #56
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    Quote Originally Posted by EagleMark View Post
    It's be cool to see how they stack up to factory specs too!

    But I don't think it's called latency is it? Voltage offset?
    In $42 it's "INJ - Injector Correction Multiplier"
    In $0D it's "Injector Offset vs. Battery Voltage"

    Or did I miss the boat?
    No, you got it right. I'd really like to have some solid offset numbers at say 22psi on 80pph injectors. It'd def take the guess work out of adjusting injector offset for increased fuel pressure. Witch hunter charges $25 per injector to measure latency or lag time, whatever you want to call it.
    95 ecsb vortec 357 10.44:1 scr LT4 hot cam single plane TBI 7427 $0D

  12. #57
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    Quote Originally Posted by gregs78cam View Post
    The only drawback that I can think of with running so much fuel through only two injectors is the pulsewidth at idle, it may be difficult for the PCM to get it to idle as lean as it should. I have found that the smallest pulsewidth I can run is around 0.488msec, which barely gets it down to stoich at a warm idle.
    You make a good point. Unfortunately, I've been dogged by mechanical issues ever since installing the engine in my truck last summer so haven't had many opportunities to tune anything, including idle.
    It seems like running a vacuum referenced FPR would help with resolution at idle? Although it seems like that may create issues elsewhere. I dunno, I'll cross that bridge when I come to it I guess.
    95 ecsb vortec 357 10.44:1 scr LT4 hot cam single plane TBI 7427 $0D

  13. #58
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    Quote Originally Posted by gregs78cam View Post
    The only drawback that I can think of with running so much fuel through only two injectors is the pulsewidth at idle, it may be difficult for the PCM to get it to idle as lean as it should. I have found that the smallest pulsewidth I can run is around 0.488msec, which barely gets it down to stoich at a warm idle.
    What PSI do you run?

    There's also an issue that comes in around 20 - 22 PSI and up which slows the injector opening. In $42 the adjsutment is "INJ - Injector Bias " "Added to the total BPW. used to compensate for injectors that open slowly." More pressure makes them open slower.

    I'd rather poop shards of glass then try to tune TBI at 35 PSI.

    Quote Originally Posted by 907 Chevy View Post
    No, you got it right. I'd really like to have some solid offset numbers at say 22psi on 80pph injectors. It'd def take the guess work out of adjusting injector offset for increased fuel pressure. Witch hunter charges $25 per injector to measure latency or lag time, whatever you want to call it.
    There is no guess, the data is there for voltage and there's no other paremeter? At 22 and 80Lb TBI injectors it's never been changed before? It's not like your putting in an injector with unknown settings where this comes into play.

    Quote Originally Posted by 907 Chevy View Post
    You make a good point. Unfortunately, I've been dogged by mechanical issues ever since installing the engine in my truck last summer so haven't had many opportunities to tune anything, including idle.
    It seems like running a vacuum referenced FPR would help with resolution at idle? Although it seems like that may create issues elsewhere. I dunno, I'll cross that bridge when I come to it I guess.
    A vacuum referenced regulator has it's place. Like if you needed 35 PSI on max size injector but could not get to idle because of what Greg said the pulswidth at idle. These are usually monster motors and works well. But a real PIA when not needed.

    If you have calculated that 22 PSI on 80lb injectors will fuel the engine then you don't need one.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  14. #59
    EFI tuning addict 96lt4c4's Avatar
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    I settled for my BB 80 pound injectors at 15 PSI and I have all kinds of fuel.

    -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. #60
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    There is no guess, the data is there for voltage and there's no other paremeter? At 22 and 80Lb TBI injectors it's never been changed before? It's not like your putting in an injector with unknown settings where this comes into play.
    As I understand it, injector offset times increase at lower voltages and vice versa, but offset times are also affected by fuel pressure... yes?
    So if an injector takes say ~700 usec to open at 14V and 12psi fuel pressure...how much longer does that same injector take to open if you increase fuel pressure 50% or 100% or 150%? It seems that this value is very important to have correct as the PCM adds it to injector pulse width, even more so at idle.

    Or am I completely over thinking this? Lol

    I'm just trying to mitigate Murphy's law for when it comes time to tune this thing...
    Last edited by 907 Chevy; 11-24-2012 at 11:36 PM.
    95 ecsb vortec 357 10.44:1 scr LT4 hot cam single plane TBI 7427 $0D

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