1997 Blazer, 4.3 no cold start

I have a problem with cold starts, there are no engine codes, have replaced the ETC sensor, cleaned the throttle body, and intake. replace the fuel filter. The only way to get it started is prime the throttle body with a small amount of fuel. it starts immediately, and then after when warm. When warm it will start without any problems. Only overnight or extended periods to cool down. then must prime again to start? Fuel pump or cold start injector?