Wife's '99 F150 Lariet with 75k miles stumbles and seems to misfire between 30-45 mph. The vehicle is equiped with a 4.6L engine. I have no experience with this engine. I did own a '87 5.0L Mustang GT however that vehicle never exhibited those type of symptoms. Can anyone provide assistance with diagnostics?

 

Im having a very similar problem with my ranger. for a vehicle with only 75k miles on it, i would bet that it is bad spark plugs or wires (if you change one you might as well change both)... however it could be something more serious like a holed piston or a bad valve. if changing the plugs and wires doesnt work do a compression test and see which cylinder is giving you problems. good luck, i feel your pain!

 

RangerGuy25 - Thanks, I replaced both the fuel filter and sparkplugs this weekend. The stumble and misfire on grades has, thus far, been resolved. The plugs look original, as did the filter. I'll update after she's driven the vehicle for a week or more.

 

MY F150 FADES AND SEEMS TO LOSE FIRE WHEN I REALLY GET MY FOOT INTO THE ACCELERATOR. I HAVE REPLACED PLUGS, PLUG WIRES, FUEL FILTER, HAD THE TIMING CHECKED AND THE CATALYTIC CONVERTOR CHANGED. IT WILL RUN FINE, THEN JUST DIE. HAD IT TO EVERY MECHANIC IN TOWN, ANY SUGGESTIONS ANYONE???