Check Engine Light on and car shakes when in 5th gear, over 50

[vikingdiesel]

Ok, so a few days ago, everything was rough and car would shake really bad above 40mph and check engine light came on. Dealer said code was P0303(cyl3 misfire) plugs were all filled with oil so I changed the Valve cover Gasket on the passanger side since thats where Cyl 3 is, from the front bumper, the 3rd plug closer to the firewall. I changed all (4) plugs and valve cover gasket, dried the coils and still the check engine ligt however, it drove better and less of a shake. So the dealer says its the CYL 3 coil, I just changed the coil as well and same problem, still check engine light on and still small vibration feeling above 40mpg, what else could it be???

 

[steagle]

it's probably another COP shorting out. this is why you should do the entire job when the problem first arises, rather than deal with it coil by coil. swap all 8 coils. replace both VCG's. if you want to be a completist, swap all 8 spark plugs. that's the only way you will get peace of mind and not have to worry about a recurring issue (well, i've heard of the problem coming back again... but for the most part, a complete repair will keep your LS healthy for years)

 

[gcwimmer]

Did the dealer clear the code, if not disconnect the negative battery terminal for about 1/2 hour and see if you get a new CEL and get it read again.

 

[vikingdiesel]

why would it be other coils when it says cyl 3 misfire

 

[vikingdiesel]

no, dealer didnt disconnect code after the coil replacement, however, i still feel that vibraton over 50

 

[gcwimmer]

Clear the old code and if you get a new CEL get it read you could have another one failing or something unrelated.

 

[vikingdiesel]

took the dealer and the cyl 3 misfire doesnt show up, just some P316 code which i guess is a RANDOM code, whats that mean? He also said it could be something to do with the Advancetrac light thats on, The car however, does have a burning smell, or could that just be the oil that got in to spark plugs wells when I changed the Valve Cover Gasket

 

[joegr]

The misfire code does not always give the right cylinder number. It's really just the computer's best guess at it. If you have a Ford specific scan tool, then you can read the misfire counts on all cylinders, and replace those coils with noticeable counts.
I would change all sparkplugs, if you haven't already. If you don't want to change out all of the coils, then buy one more. Exchange it for one of the other coils and retest. Keep swapping coils till you find the bad one.

 

[vikingdiesel]

or just pull them out a little and listen to the electrical poping sound "TICK TICK TICK" which means coils are working