help with running issue

Discussion in 'Fox 5.0 Mustang Tech' started by wewfords, May 5, 2011.


  1. wewfords

    wewfords Member

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    just build a 306 with e303 cam and expleor intake didnt have a problem tell i put the engine in it idles great but when u revvie it up the check engine light comes on and off code is code 22 for the map sesnor and after i revvie it and let it idle it stall but i can work the gas for a min it will idle again when it stall i have to hold the gas to restart it and it has 10lbs of vaccom @idle
     
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  2. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    On a Mass Air car, the MAP sensor vents to open air and actually acts to sense the barometric pressure. It becomes a Barometric Air pressure sensor. It's purpose is to set a baseline for the computer to know the height above sea level. The fuel requirements decrease as altitude increases, since the atmospheric pressure decreases. As altitude increases, it leans out the fuel flow to compensate for less oxygen in the air.

    Disconnecting the MAP or BARO sensor will set code 22.

    Misconnecting the BARO sensor to vacuum on a Mass Air car will cause the computer to lean out the fuel mixture.

    Code 22 or 126 MAP (vacuum) or BARO signal out of range. The MAP or BARO sensor is pretty much the same sensor for both Mass Air & Speed Density cars. The main difference is where it is connected. Mass Air cars vent it to the atmosphere, while Speed Density cars connect it to the intake manifold vacuum. Its purpose is to help set a baseline for the air/fuel mixture by sensing changes in barometric pressure. The MAP or BAP sensor puts out a 5 volt square wave that changes frequency with variations in atmospheric pressure. The base is 154 HZ at 29.92" of mercury - dry sunny day at sea level, about 68-72 degrees. You need an oscilloscope or frequency meter to measure it. There a very few DVM with a price tag under $40 that will measure frequency, but there are some out there.

    The MAP/BARO sensor is mounted on the firewall behind the upper manifold on 86-93 Mustangs.

    Baro or MAP test using frequency meter - run the test key on engine off. The noise from the ignition system will likely upset the frequency meter. I used a 10 x oscilloscope probe connected from the frequency meter to the MAP/BAP to reduce the jitter in the meter's readout.

    If it is defective, your air/fuel ratio will be off and the car’s performance & emissions will suffer

    Some basic checks you can make to be sure that the sensor is getting power & ground:
    Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.
    Check the resistance between the black/white wire on the MAP/BARO sensor and then the black/white wire on the EGR and the same wire on the TPS. It should be less than 1 ohm. Next check the resistance between the black/white wire and the negative battery cable. It should be less than 1.5 ohm.

    The following power on check requires you to turn the ignition switch to the Run position.
    Use a DVM to check for 5 volts on the orange/white wire. If it is missing, look for +5 volts at the orange/white wire on the TPS or EGR sensors. Use the black/white wire for the ground for the DVM.
     
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