NEED HELP! I have a 2007 f150 5.4L 3V. 36,000 miles. About every 5-10 days the truck will suddenly have a misfire. For a while it was always a cylinder 3 misfire, now its moved to cylinder 4 the last two times. I have changed the plugs, swapped the COPs to other cylinders to see if the miss follows, it does not. I have changed my fuel filter, no help. When it happens the CEL flashes then goes solid. It also idles rough. If I shut the truck off and restart the miss is usually gone at speed, but it still idles rough until the truck has been off for the night. I noticed that when I parked on a steep incline one time it begane to idle rough until the truck was level again. I've also checked the oil level and that's good. I ran seafoam in the fuel and the crankcase, also throught the vacuum lines. I am leaning toward a PCM issue. Any suggestions? Would a PCM reflash be advisable? Thanks for your Help!

 

Are you buying your gas at the same station every week or so? If so try another gas station for awhile. I have seen drivability issues with bad gas (water). Water will settle to the bottom of the tank. Parked on an angle could move the water to the fuelpump pickup and after filling up (every 5-10 days) with contaminated gas could cause the same problem until all the water was pushed through the system. Just a thought.

 

Different gas stations. Also ran two cans of seafood which is supposed to dissipate water.

 

I meant seafoam.

 

What kind of plugs did you use? Some plug brands are known to cause issues. Seafoam is poo poo, next time try Techron or gumout with regane in the tank. I assume you are getting p030x for the misfire?

 

I used champion plugs. This issue started before I changed plugs. Was getting p0303 code. Changed plugs still p0303. Swapped COPs with cylinders 1 & 3. Still p0303. About two weeks later p0304 instead of p0303. Been p0304 for last 3 times. I swapped plugs and COPs on cylinders 2 & 4 still p0304 I'll try those other brands next time. Thanks!

 

Champions have been known to cause problems. I would suggest sticking with Motorcraft plugs, plus they are cheaper.

 

Iwouldn't put seafoam in my truck.Use techron or gumout with regane. There is a possibility of hydrolocking the engine pouring it in the vacuum lines.

 

Seafoam is snake oil. There are alcohol additives that make water burnable.. Champion plugs have been know to have crack in the porcelain if you examine them closely for crack and find none they have been working for some people. I would look closely for water leaks from the heater hose in that area..