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Thread: Holley 12-300 In-Tank Pump Question (PSI)

  1. #1

    Default Holley 12-300 In-Tank Pump Question (PSI)

    My new Holley In-Tank pump is showing up on the datalog and on the handheld running at 63 psi. I have it wired correctly and I have a Holley Transducer in the fuel line right after a Summit 10 Micron Fuel Filter (SUM-230123B) and right before the TB. This is the sensor that is putting out the 63 psi. It is P/N 554-102. Does the ECU regulate this pressure? Or will I need to get PWM?

    I guess what I could do, since there are two ports on the TB, is to install a Fuel Pressure Regulator on the rear port and adjust it down to 43 PSI, with the return line connected to my original return line since my '69 Camaro is an original SS396 car with a return line already in place. The transducer would still show 63 psi unless I moved it to after the regulator. I was not expecting to do this because I thought the pump would not actually be running at 63 psi. The description on the Holley website states the pump is internally regulated to 58 psi, but if I need to lower it I have to figure out a way to do that. Another regulator at the TB would do this. The Injectors are rated to 43 psi and I don't want to damage the injectors.

    Crap! I just realized that will not change the psi INSIDE the TB, where the injectors are, LOL. I'll have to put it in-line before the TB. The light bulb came on finally, ha ha.

    System:
    HP ECU P/N 554-113 V5 Build 171 Firmware
    Terminator Throttle Body P/N 534-216
    Holley 12-300 Retrofit In-Tank Fuel Pump
    Last edited by brettallen59; 05-15-2020 at 04:13 AM. Reason: Typo

  2. #2
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    http://forums.holley.com/showthread....ents-Read-This (Initial Checks & Adjustments - Read Step #2)
    Fuel pressure is internally regulated to 58 psi, so you'd have to bypass the internal fuel pressure regulator to install an adjustable FPR (& return line) elsewhere. The fuel pump is not compatible for use with PWM (Pulse Width Modulation).
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, B&M Hammer shifter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

  3. #3

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    Danny, I don't get it. Why does Holley sell a 58 psi in-tank fuel pump and then the EFI systems are 43 psi? The 12-300 does not offer a return line, so I'll have to modify my system to run a return line into my unmodified tank. I purchased the 12-300 thinking that I could just plug it in, wire it up and it would be compatible with my HP ECU/Terminator TB. Am I correct in the fact that the two are not compatible as plug & play without the addition of a adjustable regulator? I actually thought that the ECU could control the pressure by pulsing the pump to a chosen psi. But this was my confirmation that I don't know a whole lot about this EFI stuff. Can I use a regulator and plug the return line? Will it still adjust the pressure down to 43 psi? Thanks, Brett.
    Last edited by brettallen59; 05-17-2020 at 04:05 AM.

  4. #4
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    Quote Originally Posted by brettallen59 View Post
    Danny, I don't get it. Why does Holley sell a 58 psi in-tank fuel pump and then the EFI systems are 43 psi?
    That's because you claim your fuel injectors can only operate at 43 psi. Most modern MPFI fuel injectors safely operate at 58 psi. 58.5 psi is the modern-day fuel pressure spec. Think of 43.5 psi as old school.

    The 12-300 does not offer a return line, so I'll have to modify my system to run a return line into my unmodified tank.
    Again, because you claim your fuel injectors can only operate at 43 psi.
    However, Holley EFI states the Terminator/Stealth fuel pressure can be safely increased to 58 psi (from 43 psi).

    I purchased the 12-300 thinking that I could just plug it in, wire it up and it would be compatible with my HP ECU/Terminator TB.
    You can, the Terminator/Stealth fuel pressure can be safely increased to 58 psi (from 43 psi).

    Am I correct in the fact that the two are not compatible as plug & play without the addition of a adjustable regulator?
    Again, because you claim your fuel injectors can only operate at 43 psi.
    Holley EFI states the Terminator/Stealth fuel pressure can be safely increased to 58 psi (from 43 psi). Only use one fuel pressure regulator.

    I actually thought that the ECU could control the pressure by pulsing the pump to a chosen psi.
    That fuel pump is not compatible for use with PWM (Pulse Width Modulation).

    Can I use a regulator and plug the return line? Will it still adjust the pressure down to 43 psi?
    The Holley EFI 12-875/12-876 Filter/Regulator is an option for either EFI system.
    It's been discussed on this forum before. It's not a good idea for every application:
    https://forums.holley.com/showthread...5989#post95989 (Related Forum Post)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, B&M Hammer shifter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

  5. #5

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    Thank you Sir. I apologize. I did not know this and all I have to go by is the screen in my Global File that says: "Rated Injector Pressure". Did I misunderstand this description? I wasn't "Claiming", I thought that this is what the manufacturer claimed. Only because I don't know. I was looking to gain some correct knowledge, that's all. I thought that this was a manufacturer specification. So you're saying that the injectors that come with the Terminator do not have a rated injector pressure of 43 psi? My whole frustration is based on this call out. Is this wrong? I'm sorry. I guess I'm learning that someone with moire knowledge than myself should be doing this. Brett


    Then there's the spec sheet for the throttle body & injectors. I just assume that the statement here meant that the injector can safely run only at this number, but this is only because there is no information saying it could go higher.
    Last edited by brettallen59; 05-17-2020 at 08:44 AM.

  6. #6
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    The Terminator EFI doesn't have to run at 43 psi fuel pressure. 43 & 58 psi are both acceptable. 43 psi is just it's "Rated Injector Pressure". Since you have a 58 psi fuel system, change the "Actual System Pressure" to 58 psi. Leave the "Fuel Injector Information" section as is.
    http://forums.holley.com/showthread....ents-Read-This (Initial Checks & Adjustments - Read Step #2)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, B&M Hammer shifter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

  7. #7

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    Okay! I will do that. Thanks for the help, really. Brett

  8. #8
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    You're welcome.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, B&M Hammer shifter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

  9. #9

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    Holley marketing just hasn't gotten around to updating all of their product literature. They could do everyone a big favor if they added a short note to the instructions that 58 psi is fine for all Holley injectors. They should also show a screen shot of how to change the "Actual System Pressure" setting in the program.

    Holley marketing wants more and more people to buy their EFI systems, which means that inexperienced people will be buying these products, which means that Holley needs to take some extra time in the instructions to fully explain things.

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