My father-in-law has a '97 F-150 with 201,000 miles, 4x4 w/4.6L. He has been the only owner as he ordered the truck new. This truck has been to h*ll and back numerous times, I could spend all day telling you what this truck had done, it's impressive. He's a general contractor so you can imagine the amount of lumber etc. this truck has hauled or pulled...I think most 3/4 tons couldn't do what this truck has done.

Anyways, in recent months the truck has developed a miss that causes the truck to shutter and shake pretty good. We first started to address the situation by checking for lose wires, there were none. We then replaced the plugs and this corrected the problem for a few thousand miles. The truck then started missing again, a little here and there and then become very regular. We checked wires, made sure they weren't loose or arcing, which they weren't. He then took the truck to a mechanic. The mechanic put new wires and plugs in it, which I didn't think it needed, but it corrected the problem...for a few hundred miles and then it started missing again. He needed to take the truck to Branson for vacation, so we did a quick fix, put new plugs in it before he left. This worked for about the first few hundred miles, and again it started missing. He went all the way to Branson and back with it doing this, he had no choice. Of course, the fuel mileage was terrible he said, about 13 MPG.

Anyways, when I changed the plugs before he left I noticed that the second cylinder on the passenger side was much lighter than the other plugs, almost white, but still slighty brown, as the other cylinders were a dark chocolate brown. Could the irregular color off that spark plug be a sign that for some reason that cylinder is dieing? Looking for answers...he plans on putting a new motor in as the truck is mechanically solid and looks great for Northern Wisconsin winters, but doesn't want to do this any sooner than he has to. Any ideas

 

The first thing you should do is get the computer scanned for error codes. Some of the autoplaces do this for free. That misfire could be a symptom of any one of a multitude of problems and hopefully the error codes will clue you in to what has failed.

 

Yes, you need to run a compression test first. You could also have a failing coil pack.

 

My 99 4.6 did this. It was a fouled plug or plug wire. Bought a coil pack, and before I changed one of those to see why it was doing it, I got a wild hair and changed the plugs and plug wires. This was the problem! It fixed it. Code reader was saying Cylinder 3 and four misfire I think... If my memory serves me correctly. PS If you have the 4.6 the plugs are a bit of a bitch to change!

Dave