I just Replaced my Vavle covers and since I had my Plenum taken off I went ahead and put my Kinetix Intake Manifold on that Ive been sitting on for a year for. I get everything back together and crank the car and it is missing and back firing bad and eventually wouldn’t start. Turns out I crossed 4-6 spark plug wires. Fired up still missing and back firing. So I changed out the plugs. 5-6 had oil from the old leaky valve covers I had just changed. Cylinder 1 had fuel on the ignition side. Since then I changed out all 6 plugs. Fired it up and still missing and backfiring, also smells of fuel but no visible leaks of fuel or air leaks on the new manifold or anything. (Taken everything off and put back on exact to spec and proper sequences. Also reset throttle body after putting everything together.) I’m leading toward I have something wrong fuel related with Cylinder 1. But I’m not a mechanic. So I don’t know where to go from here. Please help.

 

You might have flooded the engine when the coil pack harness connections were crossed. If you push the gas pedal to the floor (holding it there) and then crank the engine, this activates clear flood mode (ECM deactivates fuel injectors when cranking). It also helps to remove the spark plugs completely. The engine will crank over easier helping to blow out the excessive fuel build up. The plugs also need to dry out if they're soaked in fuel.

If that doesn't help solve the issue, then you might have other coil harness connections crossed or you have a potential vacuum leak on the intake manifold. Double check you have your O2 sensors and MAF sensor properly connected.

Not sure what you mean by "reset throttle body", did you perform an idle air relearn? Clear learned data? Throttle position relearn? Also, did you use OEM recommended plugs (NGKs)?
Good Luck!
-Icer