My truck was running a little rough when I tried to speed up out of overdrive around the 45-50 mph range so I decided to change the wires. I changed the plugs at 100k and now have 125k miles. It did not solve the problem as a matter of fact I got a P0302 which is cylinder 2 misfire code. Re-attached wire and reset only this time I got a p0304 code. Now the problem is getting worse because it is sputtering and missing out at lower speeds. I changed the fuel filter out say 40k miles ago and will change out tonight after work. Could this problem be a bad fuel filter since more than one cylinder is coming up? The truck idles great it is only when you speed up and try to downshift to pass, that I am having the problem. Did not have any misfire codes showing up prior to changing wires. It had original wires on it. Now I am wondering if I got some bad wires but it is on two different cylinders. Is it possible that the connection between the plug and wire is not good? You know they give you some grease to put on connection but there is no way to get it on the plug or up in the boot. The problem was pretty bad before wire change but now is worse. Any suggestions would be appreciated

 

Recheck the wires to insure that they are seated. I use a touch of Vasoline inside the boot tip to reduce the effort. I have seen people chase the mis-fire codes from cylinder to cylinder and I recall the problem being the Coil Pack more times than not. You can check the Ohms across the coils with a multimeter. I believe the the resistance should never be higher than 12K and it is not uncommon for the coil to go bad as a result of bad wires. Improving the quality of the wires does not reverse the damage already done to the coil pack.

 

The problem is resolved for now. I replaced the #4 sparkplug and its running great. I did check the resistance on both coils and got readings in the 14 range. The specs at Autozone call for a range of 11.1 to 16.6. New coils were just over 11. Can anyone confirm that this is acceptable? Maybe my coils are bad and causing the sparkplugs to fail. The wires were OEM with 125K on them so they needed replacing. The plugs have only 25K on them.

 

I received a check engine light the other day and checked it with my OBD2 reader, it said I too had a (304) misfire at #4 cylinder. It did not seem possible since I just had the plugs changed by a dependable pepb...s mechanic (yea right).
I figured to fix this I would have to do it myself, even though I did not want to do it and I paid to have it done so I thought.
Anyway, I started to remove the plug at # 4 and could not seem to grab the plug, I even thought the hex was stripped, I just could not get it. Lucky me I had a magnet, so I struck it in the hole and realized that I did grab something.
Long story short, the idiot that installed the plugs HAND tightened the plugs such that #4 was just hanging on and all the rest of the plugs was the same way.
I reinstalled everything with new wires (that they were supposed to change) and removed the check engine light.
Everything fine now that I fixed it.
You can't frickin trust anybody.