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Thread: Upgraded the fuel system. Should I use the vacuum reference on fuel regulator?

  1. #1

    Default Upgraded the fuel system. Should I use the vacuum reference on fuel regulator?

    I have a Terminator TBI system on an LSx crate engine. I just replaced the 200 LPH in tank pump with a 340 LPH pump after discovering that the Terminator system requires 255 LPH @ 45 psi. (I was losing 10 psi of fuel pressure at WOT on the chassis dyno.) I also added the Holley transducer so I can read fuel pressure on the 3.5" handheld. I had the old pressure regulator set to 46 psi, instead of 43 psi. With the new pump installed, I set the new regulator to 43 psi (evidenced by both the mechanical gauge on the regulator and the handheld reading), and changed the actual pressure setting in the ECU from 46 psi to 43 psi. I have not yet run the engine since these changes (car is on jack stands waiting for new wheels to arrive). My question is, should I begin to use the vacuum reference hose on the regulator? I've read in this forum that it should be used from the beginning, but if the ECU has Learned without it, not to use vacuum referencing or it could cause a lean condition. With all the changes I've made, I assume the system will have to re-learn anyway, so now is a good time. However, I do not want to run too lean and risk detonation on an engine with 10.7:1 compression with no knock detectors on pump gas. Thanks in advance.

  2. #2
    Join Date
    Dec 2009
    Location
    Connecticut
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    17,710

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    I'd use the vacuum reference hose, since the injectors are subjected to manifold vacuum.
    The engine will not run lean; the ECU's Closed Loop Compensation functions very fast.
    https://www.vaporworx.com/documentat...re-regulators/ (Vacuum Referenced Fuel Pressure Regulators)
    http://forums.holley.com/showthread....ith-Terminator (Related Forum Thread)
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  3. #3
    Join Date
    Nov 2014
    Location
    Ont. Canada
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    656

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    The vacuum referenced regulator does not lower fuel pressure at WOT, because there is very little manifold vacuum. So you're at no more risk of detonation than you were before.

  4. #4
    Join Date
    Dec 2009
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    Connecticut
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    Correct, only at idle, deceleration, part throttle & cruise conditions. At high load/WOT (no vacuum), it should maintain the base/static fuel pressure.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  5. #5

    Default

    Quote Originally Posted by 81 TransAm View Post
    The vacuum referenced regulator does not lower fuel pressure at WOT, because there is very little manifold vacuum. So you're at no more risk of detonation than you were before.
    My concern was running lean under normal driving conditions while the ECU "re-learned", not while at WOT. Based on Danny's reply to my OP, I'll use the vacuum reference hose.

    Quote Originally Posted by Danny Cabral View Post
    I'd use the vacuum reference hose, since the injectors are subjected to manifold vacuum.
    The engine will not run lean; the ECU's Closed Loop Compensation functions very fast.
    https://www.vaporworx.com/documentat...re-regulators/ (Vacuum Referenced Fuel Pressure Regulators)
    http://forums.holley.com/showthread....ith-Terminator (Related Forum Thread)
    I'll go that route. Thanks.

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