Rick230

Help, I have a 2003 Ford F150 with a 4.2l engine, V6. Check engine light on steady and blinks at times. Missing and shaking badly when decelerating and accelerating, went to Advanced and got the code checked, it read Miss on cyl #3, they advised me to change plugs and wires.

July 5, 2010 -Replaced Wires/Plugs - No improvement. Same code, they advised me to change coil.

July 6, 2010 - Replaced Coil - No improvement. Same code. Read here about Sea Foam and tried that.

July 7, 2010 Tried SeaFoam liquid and spray - 1 can gas tank, 1/2 can - breather hose attached to brake booster thing, 1/2 can added to oil, sprayed into manifold. Smoked badly, ran on interstate to blow out. Still runs badly.

Now still shaking, check engine light on and blinks then goes off, low short popping noise when accelerating. Shakes when running at a steady speed.

C Denny Run*

Have you checked for vacuum leaks? Have you tested to make sure that cylinder is getting spark by arking the plug end of the wire on something? The popping sound makes me thing it's detonating at the wrong time, or something. Try switching out injectors from a good cylinder and see if it moves the problem to the other one.

Fords Only

I had what seems to be the same problem with my 2000 F150 in November 2007 (72,776 miles). Took it to Ford shop and they replaced the coil pack ($101.84), 8 spark plugs (66.16) and 7 spark plug boots (132.93). Been fine ever since. The only difference from my repairs and yours are the boots. Maybe have them checked again?

Rick230

Thanks for all the info. I went through everything. replaced the plug and found that the wire was not making good contact. bent/adjusted the metal part inside the plug wire and it snaps on and has good contact.

Its running great!

Thanks.