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IZUSU NPR / GMC 4500 Problem and Repair

Discussion in 'Mechanic and Repair' started by spray_man, Jan 21, 2008.

  1. spray_man

    spray_man LawnSite Member
    Messages: 176

    I thought I would post my problems and repairs with this vehicle to help others. If you know a problem and repair on this truck please add to this post. If you know another site where I can get this type of information, please tell me.

    95.5 year turbo diesel automatic.

    Problem: Loss of vacuum
    Repair: Replaced the alternator. Comes together with the vacuum pump.

    Problem: When transmission is cold it downshifts at different speeds.
    Repair: Tighten alternator belt, or check alternator operation.

    Problem: Transmission does not shift up properly. Sometimes you can get it to shift up by letting up on the accelerator and pressing down on it again. In general, the truck is not very drivable.
    Repair: The wide open throttle switch is out of adjustment (not making contact or bad). The instructions for starting the truck tell you to depress the pedal all the way down while turning the key. Part of this procedure tells the computer that the wide open throttle switch is present. If the computer does not sense this connection you will get the symptoms described. Fix the switch, reset the computer, and start the truck as instructed on the visor. You should hear a "click" when throttle is fully depressed.
  2. spray_man

    spray_man LawnSite Member
    Messages: 176

    1994 IZUSU NPR Manual:

    Problem: All the dash light light up like it will start but nothing when the key is turned completely

    Repair: Changed the starter relay directly above the starter on the inside of the frame. There are two relays there. It is the bigger of the two.

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