LS3 Crate Motor Won't Start

[66ChevyMax]

Let me clarify it has started many times but now it won't.

This is a new crate engine purchased from Scoggin Dickey Chevrolet. It's in my 1966 C-10 and has been started many times. I have taken I on a dozen test drives and would say then engine has probably 2 to 3 hours worth of run time.

The last test drive the only thing that was changed is I hooked the alternator to the battery, gauge showed about 15 volts, drove the truck for a bout 3-4 miles and parked it in the driveway. About 15 min later I started it up again to move it into the shop, it ran for about 10 sec then sputtered and died.

When I tried to restart it didn't sound right, some knocking sounds, would sputter but not run. Pushed into the shop and called it a night.

Next day, remove power from ECM, turn motor over no noises and had oil pressure, hooked ECM back up, turns over great no noises and has fuel and oil pressure but doesn't even attempt to fire.

Any ideas or direction would be greatly appreciated.

See build thread below.