Rebuilt 454 running bad

Discussion in 'GM Powertrain' started by Crawdaddy, Aug 13, 2007.

  1. Crawdaddy

    Crawdaddy All hail the Mad King!! Staff Member 5+ Years 1000 Posts Platinum Contributor

    Hey guys!

    My uncle and I finally got the 454 back in the dually. He went to crank it up to warm the engine, and it would die after 5ish minutes of idling. He thought it was the alternator was not working, but when I put my meter on the battery, voltage when the motor was running was 13.5 volts, so it isn't the alternator. When I was testing his theory about the bad alternator, I revved it up to about 1500 rpm, and it ran nice, but when I let off the accelerator, it tried to idle, but couldn't keep a steady idle speed and died. Now it won't idle for anything :| . Anyone have any ideas as to what's going on? I'm thinking it may be the IAC (idle air controller, or something like that), but he keeps asking me if that was the problem, why isn't it throwing a code. As far as I know, the IAC isn't electronic, is it? Also, the motor is throwing a P1345 code, which is CKP and CMP sensor correlation code. From what my grandfather is saying, there is a learn process for that that has to be performed while driving. Both of the offending sensors were changed before putting the motor back in the truck. Any merit to what my grandfather said? We would drive it and attempt the relarn procedure, except that my uncle didn't put the torque converter back in in preparation to drop the tranny to get it rebuilt. Any fresh ideas are always appreciated. Thanks guys!
    Last edited: Aug 13, 2007
  2. TrailLeadr

    TrailLeadr Epic Member 5+ Years 1000 Posts

    I don't think the learning portion would have anything to do with the idle. The learning is usually just for the trans.
    IAC runs about $49.99 over at

    check out this guy's suggestion on how to test the IAC
  3. GaryL

    GaryL Epic Member 5+ Years ROTM Winner 1000 Posts Platinum Contributor

    If you are getting the code about cam/crank correlation, your distributor is off a tooth or so. Correcting this may get your idle back.
  4. Dj Friction

    Dj Friction Rockstar 100 Posts

    Actually...I was thinking the same thing....However I was not sure if you rebuilt the engine....I was thinking the timing chain maybe off a few teeth....The distributer is much easier to check....But you should check TDC in #1 just to make sure you have Cam timing.

    My Thoughts.....
  5. CaJuN625

    CaJuN625 New Member

    Dumb mode

    Unplug the computer and put the engine in "dumb" / "open loop" / "limp" mode. If it idles nice, it's a sensor giving a reading outside what the computer knows what to do with or is telling the computer to do something it shouldn't be. If it doesn't change the way the engine runs, it's something off in the timing - maybe the bolt's loose that holds the distributor from rotating?

    If it idled ok for 5 minutes ... you may have had oil supply or coolant supply issues and could have done some damage.

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