This is a used block. I am using the heads I had cleaned and vacuum tested when I did head gasket on original engine. Did head gasket before installing. New plugs and wires and injectors. Also used intake manifold, injector rail, lower intake and oil pan from my original engine. Also new oil pump, timing chain.

I keep getting misfires in 1 and 8 after driving a few miles. If I take a short trip, no misfires.

What I've checked
Dry compression
new injectors (again) in those cylinders (Bosch)
Swapped plug wires (swapped #7 with #1 for example)
Completely stripped injector harness to look for cracked wires
Moved spark plugs around
New coils
Smoke tested lines and intake for vacuum leaks
Crank sensor


Have not done leak down
Not losing oil
Not losing coolant

The codes are p1300, p0301 and p0308

It's always cylinders 1 and 8 and it's not a dead miss. Those two don't share a coil or a bank.

Not sure where to go from here, and ideas?

 

To diag further, use a scanner to check upstream O2 voltages, long and short term fuel trims, both banks. Those values should indicate whether there is a fueling problem or not. Monitor for a complete drive cycle from cold to hot. Maybe do the leak down for those cylinders, at least, engine warmed up.

 

Swap plug wires 1 and 2, 7 and 8. Maybe start with spark plugs and then if that does not change things do plug wires.. Next after that woudl be swapping coils left to right. Doing that would put #1 in to #2 position and #8 in to #7 position, making it a valid test. Next woudl be injectors. 99% chance doing this will identify your issue.