So just purchased this truck. Was told engine was rebuilt 2 years ago. (Don’t believe it). I knew there were some issues I would have to address. Basically truck idles very rough when bought it. Figured basic tune up would probable solve the problem. Hooked up my scan tool and found several misfire codes and o2 sensor codes. Removed the plugs and they were in very bad shape. Replaced all 8 plugs. Replaced with auto light plugs. Yes some people say these engines don’t like them. Only motor craft. However I have owned this exact truck in the past and always used auto light with no problems. Reset codes. Truck idles rough but accelaeration much better. About 40 miles later check engine light back on. Bank 1 lean. Bank 2 rich. Was thinking o2 sensors backwards. So started looking around. Found all o2 sensors not connected. Thought that was the problem. Connected all sensors. Drove great for a short time. Shut engine off and next turn of the key. Back to no acceleration and very rough through all ranges. Again connected scan tool and started looking at fuel trims. Same thing complete opposites at each bank. Figured it’s due so I’ll replace the o2 sensors. Both upstream and down stream. Got up stream sensors in gotta get removal socket for down streams. After front o2 changed both banks now a lean condition. One misfire of cylinder 1. This morning took fuel trim ratings again. Got the following. Bank 1 and bank 2 both switch rapidly between -3 and +3 at idle at same time. Running at normal operating temp. At 2000 rpms. Runs -8.7 on both banks. Voltage at b1s1 switch rapidly between .050 and .870. B2s1 and B2s1 s2 both stay at around .025 v. Through all rom ranges. I will be replacing the rear 02 sensors either today or tommorrow. Any other thoughts

May have found the root problem. Timing chain guides. Replaced all 4 o2 sensors. Problem still there. Took off valve cover to check for maybe a rocker that was bad or bad lifters. Found plastic pieces in the timing chain area. Only plastic that I know of that is in the timing chain housing is the guides. Which would explain all issues. Gotta order the parts and take timing chain cover off to confirm. But once confirmed and replaced I’ll post an update. Sometimes you gotta go old school and just take stuff apart until u find the problem.

I know if you had the 5.4 that you’d need to to hunting for plastic pieces in the oil pan when the tensioners break but, not familiar with the 4.6 enough to know if you need to do the same. So, just throwing it out there.

just to to be safe. I’ll take the oil pan off aswell. Gotta drain the oil and coolant anyway to get the timing cover off. Thanks for the thought. I’ll let you know what I find probable won’t even get to it til this weekend.