If the other Bank is working fine I would try to exchange parts between both banks. Starting with the Ignition system ( Distributor with arm, cables, Spark Plugs (even if there is a spark, it does not necessary mean that the spark is strong enough)), then the injectors. At some point the fault should travel to the other side.
My guess is the distributor arm or the distributor cap. I have seen the craziest faults happening with these parts. sometimes they just stop working properly when they are warm.
I would rule out the fuel system, because as far as I know there is no difference between the two banks. Same regulator and so on. And that the Ignition valves open up to short just on one side... I don´t think so. But, nothing is impossible.
