My 1998 gmc sierra will turn over but won't stay running.
It has a new starter, fuel pump, battery, and has good fuel pressure. Nothing came up on
the code scanner when plugged in either.
It may be the famous GM passlock security that is not allowing it to stay running: https://www.youtube.com/watch?v=yDRwkEFLq-U
If you find that this is your issue, refer to the following PDF and try the re-learning procedure. Your vehicle should have the Passlock (coded cylinder) type security. http://my.cardone.com/techdocs/pt%2077-0011.pdf
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