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Thread: Question regarding vacuum for MAP sensor.

  1. #1

    Default Question regarding vacuum for MAP sensor.

    I'm running a Holley 112-588 throttle body (4150 style) on a Holley manifold with a Gen3 GM ECU. Can anyone verify whether I should pull vacuum for my MAP sensor from one of the "full manifold" vacuum ports, or from the "timed spark" vacuum port on the front of the throttle body? I'm currently pulling it from a port in the manifold just below the throttle body, but it doesn't want to start properly (it sounds like a cough when it starts and sometimes cranks too long). Just trying to troubleshoot the problem. I have replaced the cam sensor with no improvement. Thank you!

  2. #2
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    The MAP sensor must measure full manifold vacuum only (not the timed spark port).
    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. #3

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    Thank you Danny, much appreciated!!

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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 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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    Quote Originally Posted by cwmusser View Post
    I'm running a Holley 112-588 throttle body (4150 style) on a Holley manifold with a Gen3 GM ECU. Can anyone verify whether I should pull vacuum for my MAP sensor from one of the "full manifold" vacuum ports, or from the "timed spark" vacuum port on the front of the throttle body? I'm currently pulling it from a port in the manifold just below the throttle body, but it doesn't want to start properly (it sounds like a cough when it starts and sometimes cranks too long). Just trying to troubleshoot the problem. I have replaced the cam sensor with no improvement. Thank you!
    Your MAP sensor will still read the same, since both your current location below the throttle body, and a manifold vacuum port on the throttle body are the same vacuum. Your vacuum hose should run UPHILL from the vacuum source to the MAP sensor. In other words, the MAP sensor needs to be mounted HIGHER than the vacuum source. Gary
    Last edited by Gaz64; 01-07-2019 at 06:21 PM.
    Regards, Gary

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    Gaz64, he was referring to the "timed spark port" on the throttle body, which has no vacuum at idle and can not be used for a MAP sensor.
    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.

  7. #7
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    Yes, I know how it works Danny. The OP was also asking about moving from his current location, which is manifold vacuum, and moving to "full manifold vacuum" on the throttle body. Hardly worth the effort.
    He has a starting issue, so unlikely to be MAP sensor hose routing issue. Hopefully he is reading all of our replies. Gary
    Last edited by Gaz64; 01-08-2019 at 04:11 PM.
    Regards, Gary

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    Gaz64, I never said he needs to move anything. I simply answered his question, "The MAP sensor must measure full manifold vacuum only (not the timed spark port)." Whether it be from the throttle body or intake manifold.
    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.

  9. #9
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    Quote Originally Posted by Danny Cabral View Post
    Whether it be from the throttle body or intake manifold.
    Glad we agree on that Danny. Gary
    Regards, Gary

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