If its an obd 2 car,the absence of a cat may have an effect due to the secondary o2.
Usually a clogged filter will LOWER fuel pressure causing a lean condition considering the fact that it is it is in line before the injectors.
It may be a clogged fuel pressure regulator return line causing a deadhead of the fuel system after the injectors?
If the timing was set incorrectly on all three motors that may also be your problem.
Cheap or ebay chipped ecus can also cause problems.
hope this helps...