'98 Suburban Lacks Power

Discussion in 'GM Powertrain' started by SuburbanSS, Sep 10, 2009.

  1. SuburbanSS

    SuburbanSS Member

    Hey all,

    I have a problem where it seems like the truck is pulling a 20,000lb trailer and it has absolutely no power.

    Basically an almost full overhaul:

    Recently rebuilt Motor & tranny. Idles great about 1,000rpm soon as you put it in gear it bogs right down to about 500rpm and barely can move out of its own way.

    New Ignition Coil, Module, Plugs, Distributor, Rotor, Cap,
    VSS, Crank Position Sensor, IAC, TPS, MAP, MAF, PCM

    And the only code it is throwing is the

    P0108 - Manifold Absolute Pressure (MAP) Sensor Circuit High Voltage

    I'm not really sure how to read this, is this an overlimit on the value it is expecting because of the sensor working as intended or is this an electrical issue where it is receiving to much voltage? And would it explain the engine lacking power?

    Just at a loss as the codes dont seem to be telling me much, and just can't seem to get power out of this motor.
  2. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    The high voltage basically means the computer is seeing an open circuit on the MAP sensor. This is your lack of power problem. Make sure the connector is good to the sensor and then check the vacuum diaphragm. It must hold vacuum. If it doesn't it will set this code. You can check it with a Mighty Vac and watch the feedback with a DVOM or if you have access to a scanner thats the best way to watch the feedback because you know the signal is reaching the computer.
  3. 2COR517

    2COR517 Epic Member 5+ Years 1000 Posts

    The MAP likely explains the fast idle problem too.
  4. SuburbanSS

    SuburbanSS Member

    I tested power supply to the connector and verified the 5v supply it should be getting was right at 5.01, and in terms of testing vacuum what would be the best method of testing it, hooking up a mighty vac to what exactly?

    This is going above my head in terms of troubleshooting vehicles.

    Thanks for all the help in advance...

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