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95 5.7 engine light, not idling down during shift, slamming thrugh the gears.

Discussion in 'Chevy Trucks' started by bgingras, Jul 12, 2010.

  1. bgingras

    bgingras Senior Member
    Messages: 282

    1995 K2500 with 5.7 4L80E transmission

    My engine light just came on and now it's slamming into gears, as in the engine doesn't idle down at each time the transmission shifts. It's fine if I let off the gas right when it shifts, otherwise it feels like I'm being hit from behind. This happened when the engine light came on couple hours ago. I cannot find a scan tool anywhere for this vehicle to get the code...anybody got any ideas? I'm heading out to the truck to start looking for loose/broken wires or sensor. Maybe?

    ugghh
     
  2. bgingras

    bgingras Senior Member
    Messages: 282

    now I have a code #43 flashing, but cannot find a list of codes.
     
  3. bgingras

    bgingras Senior Member
    Messages: 282

    disregard. Knock sensor wire was broken. All fixed...who knew a knock sensor would also cause such shifting issues.
     
  4. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    It most certainly will. When the ECM doesn't get a report back from the knock sensor it defaults to a fixed timing curve, thus affecting driveability and/or idle speed but on a 4L80E equipped truck especially what it (the ECM) also does is command full line pressure to the trans as a safety default hence you can have harsh shifting. It does so to protect the trans as it knows there's a problem somewhere in the system that could affect the holding ability of the trans at normal commanded pressures.
     
  5. bgingras

    bgingras Senior Member
    Messages: 282

    good to know.