Have a 96 c1500, 4.3, auto. Just rebuilt the engine at 178,000 because of coolant leak in intake manifold gasket. Contaminated oil was everywhere and a sweet chocolate brown at that! Had crank ground 10/10. Cylinders good at 3.997 to 4.00 and new standard size rings installed. Heads came back from machine shop with a valve job and a freshly milled surface.

Assembly was straightforward except for cam bearings - used two boxes to fit the journals and the cam bearing faces.

Engine turned over and fired up right away and ran roughly for about 3 minutes before I realized that I had reversed #3 and #5 wires! I started it again and it ran much smoother - but only for a minute before it died. Now it is down to about 5 - 6 seconds.

Here's the situation:

Engine starts and runs sweet for up to 5 seconds then dies.
Fuel pressure is 60 psi at start then drops to 50 psi and holds.
Disconnected Y pipe to eliminate potential catalytic converter pluggage.
Replaced fuel filter and fuel pressure regulator.
Distributor, cap, rotor, wires and pliugs all new.
Timing spot on.
Oil pressure shows 50 psi and is a new sensor
All controls connected and re-checked twice.

I guess it must be something in the engine control system or the emission control system. I am at a loss since these are part of what was a running engine. No harsh cleaners were used on sensors.

Anybody got a good idea or two?

Thanks in advance

 

1st, is check engine light on? 2nd, are ALL sensors, connections, wires and such hooked up right and solid? 3rd, if memory serves, fuel pressure shouldn't go below 55psi, so possibly fuel pump going out. also, could be fuel pump relay, ignition coil, ignition module.

 

I am with maxx. it's got to be gas or spark. a good to start is to find out what one is giving out to help point you in the right direction.