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Thread: 1 Bar MAP reading 100 kPa - Scaling Question

  1. #1

    Default 1 Bar MAP reading 100 kPa - Scaling Question

    I have the HP 550-606 Kit for a SB Ford N/A with a Holley 538-24 1 bar MAP sensor. I have the correct MAP sensor selected in the V5 EFI software and my kPA at idle is ranging from 99 to 101 on various days. I live on the east coast at sea level and my Base Fuel Table shows me idling in the upper left area of the table. The Learn Table is also reading in the top left and maxing and out at 105. When I set the Target AFR, I'm setting the top rows only as I'm unable to go higher. I tried to change the scaling range however, it will not let me go over 105. I'm trying to set the Base Fuel Table from lower left (idle) to upper right, however, my idle and RPM range is top left (101) to top right and maxing out at 105. Am I correct in thinking I should be scaling the MAP from estimated 60-210 kPa range if I'm idling at 100 kPa? If correct, how can this be accomplished? Custom MAP/custom scale? Thank you
    Last edited by splithigh; 02-02-2020 at 02:19 PM.

  2. #2

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    Sounds you have a bad MAP sensor. 1-bar MAP ends at about 103 kPa and 29" of vacuum is about 0 kPa. There is no rescaling. Easy to test, just draw a little vacuum on the MAP hose - the kPa should drop. This can be done with the engine off! Just connect and watch the football as you draw vacuum. Make sure you have a 1 bar MAP sensor is selected in the Sensors ICF.

  3. #3
    Join Date
    Dec 2009
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    Connecticut
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    24,204

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    Or your MAP sensor hose isn't connected to intake manifold vacuum.
    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, 232°-244° duration/.623" lift/114° LSA camshaft, 11.8:1 comp, TFS R-Series FTI ported intake, BBK 80mm TB, 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, 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 MT tires.

  4. #4

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    Yeah...that too, LOL!

  5. #5

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    Well...that was the problem. Vacuum line was not hooked up (I can't believe that I missed that). I've been fighting with tuning for a bit (lean spike, etc.). Reset everything and running good. Now I can focus on smoothing the Base Fuel Table and dialing it in. Thank you both for your help!

    I'm still having issues with the IAC slowly returning to 0%. I set it at 5% at hot idle and it slowly (60 sec +/-) moves to 0%. I'm always doing a TPS Autoset. I checked for vacuum leaks by capping off the throttle body and the engine died immediately. Only have a couple of vacuum hoses and they are new. Should I smoke test or spray water around the gaskets to test for leaks?

  6. #6
    Join Date
    Dec 2009
    Location
    Connecticut
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    24,204

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    Quote Originally Posted by splithigh View Post
    Well...that was the problem. Vacuum line was not hooked up (I can't believe that I missed that). I've been fighting with tuning for a bit (lean spike, etc.). Reset everything and running good. Now I can focus on smoothing the Base Fuel Table and dialing it in. Thank you both for your help!
    Thanks for the update.

    I'm still having issues with the IAC slowly returning to 0%. I set it at 5% at hot idle and it slowly (60 sec +/-) moves to 0%. I'm always doing a TPS Autoset. I checked for vacuum leaks by capping off the throttle body and the engine died immediately. Only have a couple of vacuum hoses and they are new. Should I smoke test or spray water around the gaskets to test for leaks?
    If the IAC Position decreases to 0%, then the engine is inhaling air from an additional source - vacuum leak.
    This is assuming you've adjusted the idle speed screw on throttle body to achieve an IAC Position of about 5% at hot idle.
    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, 232°-244° duration/.623" lift/114° LSA camshaft, 11.8:1 comp, TFS R-Series FTI ported intake, BBK 80mm TB, 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, 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 MT tires.

  7. #7

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    Do you have a PCV valve on the engine? If so, plug it and see if the IAC stays steady.

  8. #8

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    Thanks for helping. Yes, new Motorcraft PCV valve, PCV grommet and vacuum hose. The grommet was a little loose so I used a little RTV around the grommet to seal it. I'll try that and report.

  9. #9

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    You misunderstood my post. Unplug the PCV line from manifold vacuum and cap the manifold fitting so you don't have a leak. Then see if you can get a stable IAC reading. If you can, you have a clue. This is just a test so you can figure out what's going on. Once you know what's going on, you can make a decision about running a PCV with an IAC. That might be a whole different discussion.

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