Hi all,
I have an 89 Wagoneer with the 4.0 and it recently started misfiring. It happened after my fuel injectors started leaking and I replaced the O-rings. Then the actual injectors started leaking and I got a new set. After I stuck these in, it started misfiring harder. Since then I've replaced the fuel filter, fuel pressure regulator, o2 sensor, and spark plugs. I know it's getting enough fuel because all 6 of the spark plugs are wet with gas so I'm thinking the fuel/air ratio is off and am not sure what could be causing that. I'm fairly certain it has to do with fuel and air and is not ignition related because it started after I did the injectors. If anyone has any thoughts that would be great.

Are you absolutely positive you have the injectors wired correctly? ..... since it started after you replaced the o-rings

What replacement injectors did you put back in?

I am positive. Before I started taking them out I got a paint pen and marked the wires to the right plug in. Since the wires sat in the same position for 34 years that also made it easy.

Some injectors flow a radically different rate depending on who sells them...check your injector flow on 2 or 3 different sites to make sure they flow similar to what you expected. 1/2 to 1 lb difference is not extreme... 2 or 3 pounds is

I used OEM remanufactured Siemens off of ebay. Before I stuck them in I cycled a cleaner through them to make absolutely sure they were clean and to make sure they worked so I know they are shooting.

It was just about 1/2 pound so good I'm thinking. One thing I forgot to mention was black smoke is coming from the exhaust so that's another sign of it running rich.

If it were me, I would be suspicious of those new fuel injectors, but the prudent thing to do would be to perform a fuel pressure test. 31 PSI while running, 39 PSI while running with the vacuum line disconnected.

This^^^ and this: