Not too long ago i posted about a fuel concern. I stated that at about 3500 - 4000 rpms, my car would start puttering. I had a full tank of gas and i just replaced the fuel filter. If this happens to you... try not to drive your car. It is a sign of catalytic converter. The 2.5l high output engines have 3 catalytic converters, and all of them have to be replaced. If you are not a do it yourself person and have ford mechanics do this job for you, you are looking at $2500, i know from experience.
