My '97 F150 XL w/ 4.6L was/is running rough. I had it checked and the codes it showed were p0304 (cyl#4 misfiring) and p0401
(egr flow insufficient). I replaced the plugs and wires. The truck is STILL running rough, just the same as before. I will replace the egr stuff today, but need to know the next thing to look at for the misfiring problem. I have two modules (one on each side) attached to the plugs ... could the problem be one of those ? or should I look at something else ??

 

Is it remotely possible that you have a fuel related misfire? Maybe a few minutes with a noid light on your harness will indicate that your injector is at least receiving the signal to trigger. Just a thought.

 

I finally got it figured out ... one of the coil packs were bad.
The easy part was replacing it, but there's not a good test to check it ...
Thanks for the responses !!

 

Coil packs are easily checked with a $10 spark tester.

 

I have a code P0401 (EGR flow insuf) I have changed the EGR valve and it didnt help, I dont have a miss engine runs good. Not sure how the coil would affect the 401 code but I would sure like to get rid of the engine light.

 

Try unplugging the negative terminal on your battery. This sometimes resets the computor.