1997 Chevrolet Express starts hard - fuel problem-help

1997 Chevrolet Express Van 5.7 V8 160,000 miles

Eng replaced - fuel pump replaced - ran well about 4,000 miles - now starts hard- initally suspected the fuel pressure regulator, switched to suspect the backflow valve in the fuel pump. Starts with starting fluid sprayed in air cleaner - occassionally starts by turning key on and off three or five times before cranking engine - then engine stumbles a second when starting - if engine should stall upon starting then key switching off and on will not work again, must use starting fluid to start. Starting without starting fluid is becoming rare. OBDII scanner shows the code P1406. Currently trying to find meaning for P1406 code.
 

The P1406 should not cause a no-start unless it is shorted out and taking the reference voltage to ground, thereby causing the ECM circuit to be dead. Here is a link to Chevrolet trouble codes and links to generic testing pages. Clicky---clicky. If the EGR is hiung open, it may also cause a hard start. Good luck and let us know. I usually do the Ford thing, but trying to expand my horizons along with my waist. Hopefully one of the others that has more experience on GM will drop by.