1998 chevy k1500 5.7... long block swap, new water pump, new plugs wires distb. cap and rotor. upgraded the CFI injection to MFI. Everything is back in place, it turns over and fires a little, idles for about 3 seconds (very roughly) but wont stay running. Doesnt run long enough to set a code. Has fuel pressure, has spark, timing has been set with Rotor pointed at #1 cylinder on compression stroke. I've checked the wiring and sensor for and replaced the crank position sensor, it was good. Checked all the grounds, seem to be all hooked up. Still does the same thing. Cant get a code to even get a starting point...any ideas anyone????