2003 Accord 3.0L no start after engine swap

Hi, we put in a used engine (2003 Accord 3.0L V6) from a Junkyard over the weekend, and now it won't start. It'll turn over and fire on a couple cylinders, but not enough to start. Doesn't seem to matter if spray a little starting fluid in the Throttle body while trying to start it. Anyone have any ideas? Or seen this before? It sounds normal while turning over, put in a new timing belt while it was out, and turned it over by hand 6 times to verify correct install before reassembling. I appreciate everyone's time, thanks for reading.

Figured it out. The new engine must of have been sitting awhile, one of the injectors was clogged, so it was only firing on 5. Switched in the injector rail from the old engine and it fired right up.

So, now it starts right up, runs, but misfires on all cylinders. New engine sounds good, besides the constant stumble. If I clear the codes, it runs a little better for a few minutes, but then the service light comes back on anytime you're in the throttle, eventually stays lit. I drained out a few cups of fuel, and the first couple didn't smell like gas, and were pretty dark in color, so I drained out 2 gallons (it was nearly empty at this point), and put in 5 fresh. Didn't run any different. Next day I took it to work, filled up on the way, and a hundred miles later I was down a half a tank. If you're all the way in the throttle, it'll come out of it, but that's the only time. I've checked fuel pressure, 60 running, and re-verified the timing belt we put on before installing the new engine. Everything seems fine. I'm going to try running it without the cat tomorrow, but I'm out of ideas otherwise. All codes come back within minutes of clearing, and these are the only codes that come up. P0301, P0302, P0303, P0304, P0305, P0306 and P0300

As an additional note, before we swapped out the original engine (had a little noise and one blown out spark plug) all the same codes were present (plus a couple more that haven't came back), so I'm confident the daughter bought a tank of bad gas, and that led us to finding out about the plug.