put timing chain and waterpump on 2 months ago,ran excellent.now it will start for 20 seconds and shut off,42 psi on fuel and fire great.scan tool says security problems, what could this be?

 

(I know this is an old thread and I figured its already solved)

But if its security then it would be the Vats system either the ignition cylinder or the vats module (or fuse for vats) could also be a worn key aswell.

Easy fix after checking would most likely be just bypassing the VATS system with a resistor, you need to measure the resistance value from the resistor pellet in your key, then get a resisitor to match and put it across the two VATS wires under the steering column which are two thin wires usually in a orange wire loom. (not to be confused with the yellow SRS wires).