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Thread: Question on Actual System Pressure setting.

  1. Default Question on Actual System Pressure setting.

    Have my Actual System Pressure set to 43.0 psi, using Holley 48 lb/hr 522-488 injectors. Also have vacuum reference Kirban *adjustable* Fuel Pressure Regulator (FPR) on the return line fuel rail, this is a Stealth Ram configuration. With the engine running, I've removed & plugged the vacuum line to the FPR and adjusted my FP to be 43.0 psi. Verified with underhood gauge, and in Holley software Online Fuel Pressure sensor value. Connect vacuum line back up to FPR, it lowers the FP to about 34-36 psi at idle. Driving the car around under various load conditions, FP rises as vacuum drop as you would expect.

    Now, what I've observed (reviewing datalog) is when I WOT the car (with my foot mashed to the floorboard), the highest TPS % I can get is 92% & MAP to 100 kPa, BUT my Fuel Pressure does NOT actually get to the 43.0 psi, the highest it goes is 40 psi. Do I need to be concerned with the fact that my WOT real driving Fuel Pressure is not matching the 43.0 psi setting for Actual Fuel Pressure (3 psi less) in system settings? Here is the datalog (screen shot) showing the 92% TPS, 100 kPa MAP and 40 PSI Fuel Pressure. I do have my REV limiter set to Fuel and Spark 5500L to 5800H, so I was coming up on it.

    Note, 92% is all I can get the TPS up to with the Key-On/Engine-Off to moving the throttle manually under the hood (58MM TPI style), and I've done countless TPS Autosets. In fact, I used a trick from Danny C to help with TPS sometimes jumping between 0%-1% at idle by doing an TPS Autoset, then backing off the stop screw just a tiny bit to make sure it's always 0% or approximately -0.1% or less. I don't think there's any causal relationship here however.

    Any thoughts or suggestions, or should I just leave it be? Would 3 psi be enough in the fuel flow calculations to warrant to change my System Actual Fuel Pressure down from 43.0 to 40.0; or should I turn up the FPR to read 46 psi with vacuum reference removed, and leave the System Actual Fuel Pressure setting at 43.0? Thanks in advance. Frank



    HP EFI V4, 388cid Stealth Ram, 1000 CFM 58mm throttle body, Holley Dual Sync Distributor. LS Coil Near Plug, 1 bar MAP, 48 lb/hr Holley EFI injectors, 43 psi

  2. #2
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    Quote Originally Posted by 383_StealthRam View Post
    Do I need to be concerned with the fact that my WOT real driving Fuel Pressure is not matching the 43.0 psi setting for Actual Fuel Pressure (3 psi less) in system settings?
    No. I'd be more concerned with the TPS sensor issue.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 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, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 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 tires.

  3. Default

    Thanks Danny, I've already replaced the original (stock) TPI TPS with a Standard Parts TPS, and again more recently with a genuine GM (ACDelco) one, and still haven't been able to ever get it to reach 100%. Never really worried too much about it til I review a WOT datalog. I don't "race" the car, so WOT is not a usual operating condition for me.

    I may just bite the bullet one of these days and order the Holley EFI 58mm Throttle Body to replace the one I have. I'm using a (bought new in circa 1993) ACCEL/LINGENFELTER 58MM unit. Don't feel any wear/tear on it, but maybe just something else is wrong with it who knows.

    I forgot to note in my OP my other question was if the 3 psi less of FP could be why the CL COMP% was adding 6% fuel up there to maintain AFR? Thanks as always, and appreciate all the help you provide in these forums. -Frank

    HP EFI V4, 388cid Stealth Ram, 1000 CFM 58mm throttle body, Holley Dual Sync Distributor. LS Coil Near Plug, 1 bar MAP, 48 lb/hr Holley EFI injectors, 43 psi

  4. #4
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    Quote Originally Posted by 383_StealthRam View Post
    I forgot to note in my OP my other question was if the 3 psi less of FP could be why the CL COMP% was adding 6% fuel up there to maintain AFR?
    No, it's just your Base Fuel Table was a little lean in that particular area (for 40 psi fuel pressure). Since 40 psi is your WOT fuel pressure, that's what you'll tune it with.

    Thanks as always, and appreciate all the help you provide in these forums.
    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 TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 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, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 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 tires.

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