Deedee

I have a 98 k3500 5.7 V8 chevy pickupThe truck was running perfect and then we went to are storage unit to drop some stuff off and when I came out and the truck wouldn't start it will start up then die. Start up and die I have now replaced fuel pump, fuel pump relay,fuel filter,plugs, wires,idle air control valve,cleaned the fuel pressure regulator. And still the same issue.. I had a friend stop by who brought over a pcm from a 96 and we put it in my truck and it started right up except now straight fuel was coming out my exhaust and the check engine light is blinking. Issues I've never had before with the truck I just read about security lockout and wonder if that is what the original issue with my truck was but the only thing is my security light was on for days before this all happened but it went off and has been off ever since

Gumby22

If you’re still needing an answer here…

The issue you describe is definitely the Passlock (security) system disabling the fuel. It’s designed to allow the fuel pump to prime at key on but prevents the pump from running if the system “thinks” there’s a theft attempt.

Given that the passlock light was on for several days, you need to check for codes - the PCM should have something stored in it to give you a place to start looking.

The most common problems with the Passlock systems of this era are the sensor and wiring in the column. Removing the trim shrouds from the column and inspecting the wiring is a start.

Also note that the PCM’s are not a “plug and play” application after the 1996 model year. Despite being of the same era, there were several changes in programming between 96 and 98 - I’m surprised the truck started at all with the 96 PCM.