Misfire Issues

Hello all, I am truly lost here if someone could help. A year ago I kept having misfire issues, eventually just replaced all spark plugs and all ignition coils, everything was running great, about 6 months ago I started receiving a po430 code and another talking about the o2 sensor, I don't remember what the specific code was, but I had just spent a ton of money replacing the alternator, starter, and timing belt, so I just cleared the code and moved on, it didn't come back for several months. About 2 weeks ago it came back for a day or two and went away, now 2 days ago I got a misfire in cylinder 8. I had read that a downstream o2 sensor that was bad could cause misfires and I saw another forum that talked about switching the o2 sensors across and if the code switched from 430 to 420 you know it's a bad sensor but that code hasn't come back but I'm still getting the misfire code. I went back to the basics and switched ignition coil 8 with 7 to see if the code switched and it did but it also didn't. Now I have a misfire code in cylinder 7 and 8. I switched it 7 and 8 back and switched the sensors back and just bought a new bank 2 downstream o2 sensor still thinking that was my problem. Even after switching the coil back, it still is misfiring in 7 and 8... anyone know what is going on here? I also put in cataclean to clear the catalytic converter and have been trying to drive it around but the misfires make it a bit sketchy to do so. Could it be a bad fuel injector or 2? I'm really so lost and don't want to pay a mechanic if I can help it.

 

Similar situation with my ‘12 4.6. Any feedback would be greatly appreciated

 

Downstream o2 sensor cannot cause a misfire. #8 coil is the prime suspect and should be replaced. Misfires can also come from other issues like low compression and failing injectors that deliver too much or too little fuel. Bad head gaskets that allow coolant in can also cause them, as can too much air due to a leaking intake gasket, at least at throttle less than ~50%

 

I have replaced a number of coils and plugs all on the odd bank. Keep getting misfire codes.

 

Has to be either injectors or something internal. You can swap the injectors, pretty straightforward just a couple bolts and unplug and move the injector.

I would probably start with doing a compression test and see how the misfiring cylinders compare to other cylinders. If the compression is ballpark the same then you know it's not a compression/valve issue and then I'd go ahead with moving injectors.

 

Long shot, but check your grounds. Check the battery's ground wire, mine snapped and I was chasing a misfire that would jump. Mine started in Cyl 5, jumped to 7, then would hope all around. The wire that went to the fender wall was just hanging out. When I noticed this all misfires went away. I would follow what @snivilous stated though.

 

Thanks guys. Really appreciate the input.