engine misfiring, driving me crazy - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars

collazoscesar · 08-26-2008, 07:42

Hi, my 97 expedition 5.4l was running rough, the engine light came on so i took it to meineke and they told me that the #2 coil is misfiring. i then changed all the plugs and changed only the # 2 coil. the trruck ran better but, i noticed that at about 35 to 40 mph it misfires, but the check engine light has not come on. i can't tell if it's another coil thats gone bad or there is another problem. i installed a new few filter, fuel cleaners, used better gas etc, but cant get the misfiring to stop. im hoping the check engine light will come on an identify a bad coil, but it's not. any suggestions on what else to look for. all help is gratefully appreciated.

**360ci** · 09-07-2008, 09:46

Drive the vehicle in 3rd gear (don't use over drive). Take it on the interstate up to 65mph and see if you notice any change. If the sound that you've been hearing is gone then chances are everything's fine. Why 3rd gear? ...because it's a true 1:1 ratio and allows you to get the engine rpm up higher giving the engine what it wants - to run! Running at 3000rpm on the interstate won't hurt the engine any. If the noise is worse, then take it in for a diagnostic even if no codes show as there may be a code stored away that Meineke missed during the original scan. An engine code can be stored for as many as 50 restarts of the vehicle and the light may shut off after as few as two starts. if they reset the PCM you shouldn't get any codes. If you don't notice a misfire on the interstate in 3rd gear then just leave the vehicle alone, no sense in putting more money into it unless it's necessary. There's only so much a person can do as far as regular maintenance goes as gremlins can be hard to find, let alone diagnose.