New engine not running right

Discussion in '96+ Vortec Performance + Computer Swaps' started by Saab84mw, May 22, 2020 at 11:08 PM.

  1. Saab84mw

    Saab84mw Newbie

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    As some of you may know by my recent post I’ve been working on replacing the engine in big green.

    99 K2500 Suburban 7.4

    It was rebuilt at an engine shop they punched it out 40 over and put a comp cam shaft in it I will post the card on it so I got it installed and started it up today and it’s not running very well almost like the timings off a tooth. I set up a distributor to top dead center. It rev,s up to about 1500 drops down to 500 and Keeps going up-and-down up-and-down until it shuts off. I will post a video of it.

    Could it be too much cam for the ECU or could it be the timing off just a tooth or two?

    15A7D2CF-156D-4EC1-83AB-9F062594413A.jpeg


     
  2. Awest623

    Awest623 Lifted Rides Better

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    I'll preface this by saying that I've never messed with a 454 vortec. But it sounds like it needs a tune. The stock computer ain't set up to compensate for changes that big. Do you have any way of logging data from the computer? I.e., codes, ltft, stft, spark advance, 02 voltage, etc.
     
  3. Awest623

    Awest623 Lifted Rides Better

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    Does holding down on the pedal to keep it out of idle make it run smoother?
     
  4. Saab84mw

    Saab84mw Newbie

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    Not at this time and it will not accelerate at all soon as you try to give it any throttle it shuts off

    The only sensors I did not replace was the two sensors on the Throttlebody and the crankshaft sensor.

    was not having an issue with any of those sensors before the engine went south

    when I get back home I’m going to double check the distributor to make sure that it is placed correctly and not one tooth off.

    several people I talk to about the camshaft upgrades said that I should not have to do a tune on the computer they said it would function better with a tune but was not really required to make it run.

    The tune was part of the future thing to have done.
     
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  5. Awest623

    Awest623 Lifted Rides Better

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    That is odd. Good luck. If it doesn't help see if you can pull some data from the computer. Can get most everything you need to know from the phone scanners they have now.

    Sent from my Samsung S20 using Tapatalk
     

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