Dragstr05 said:Misfires can be intermittent, and it COULD be coincidence that when you removed the tune, the issue stopped. Just take 10 mins or so, and get a 7mm (I'm pretter sure its a 7), an extension and ratchet, and pull each coil and check for cracks, unless the predator tells you which cylinder is misfiring. It only takes about 10 mins, and you can take the extra time to check the plugs too if you want. If the plugs and coils check out OK, then I would say you have a problem with the tune, or something related to the tune.
At my shop, I have never seen any 4.6/5.4 with a misfire that wasnt caused by a coil or a plug. Given, these are stock cars, but 99% of the time, its just a bad coil.

Dragstr05 said:The plugs I cant really tell you if they are bad, only that in a tuning sense or in a modified car, if you pull a plug out and its white, then you are running lean.
The coils are on top of the engine just under and to the side of the fuel rail. There are 4 on each side, 1 for each cylinder. If you took the plugs out, then you took the coils out, because the coil is what sits on top of the plug. Hence the coil-on-plug ignition...there is no distributor. And how do you know you are misfiring? Did you have it scanned for codes? If it is misfiring, it will turn the check engine light on. If that is the case, have it scanned for codes. The scanner may or may not say which cylinder is misfiring...the ford scanner does. If it is infact misfiring, the cheapest route if you arent sure is to just replace the plug. Its just a few bucks. If a plug doesnt fix it, check the coil for cracks (if you didnt already). If it has cracks, replace it. It will probably run you $70 bucks or so. I have seen them as high as $140 on a navigator. Try the plug first.
The thing with coils is that any one can go bad at any time. Thats why misfires are common on the coil-on-plug design. You just replace them as they go bad.

Seraphitia102 said:Are you using 91 octane premium gas?
