I know I really shouldn't post this here since it pertains to my dad's '03 Marquis(4.6L), but it's the best place where I can get help. I pulled a 303 code off his car yesterday and it translates to #3 cylinder misfire. The car shakes when idling and when traveling. I couldn't find the cylinder layout under the hood, so I couldn't find the #3 plug. From what I've read, it could be a coil pack, plug boot or the plug itself. The car does not have a lot of miles on it. Are there any procedures on this site that pertain to how to identify the coil packs and how to change the plugs? I have experience with coil packs and plugs from working on my Maxima(my other vehicle is a 94 Bronco XLT). I just don't want to start taking stuff apart before I know what to look for. Thanks.

Joe

 

Number 3 will be the third one back on passenger side (right side) of engine. and yes it can be anyone of the problems you mentioned above. in the tech info is information on changing plugs on these engines. make sure and use a high temp antiseize made for aluminium heads and a torque wrench when you put the plug(s) back in. if you have to replace the plug(s) use the correct motorcraft plug or autolite equal.

 

Thanks for responding.

 

try swapping a coil and see if it helps

 

4 8
3 7
2 6
1 5

front

I agree, probably the coil, and swapping it to see if the code follows is the cheapest way to test it.