2002, mercury, grand marquis, car shakes going upgrade

153346 miles. Has been running fine until last night driving at about 35 degrees F in rain going upgrade in overdrive the car starts to shake between 45 and 65 mph. Fuel tank reads 1/4 remaining. Let off foot feed and the car stops shaking. Does not stop shaking for miles on flat or upgrade terrain when foot feed is depressed. Lock out of overdrive and the shaking stops regardless of terrain. Re-fuelled within 20 miles of start of the shaking. After re-fuelling car runs well in overdrive with no shaking for the 20-mile remainder of our journey. Spark plugs have never been replaced. Would poor fuel cause this problem? Should I use a fuel additive?


1 thought on “2002, mercury, grand marquis, car shakes going upgrade”

  1. Poor fuel and poor spark together would cause an issue for sure. With the mileage you have and not ever having the plugs replaced it might be time.

    I recommend having the spark plugs and fuel filter replaced a a minimum. Oil change too if its been a while. This is just for regular maintenance purposes. Not to sure what was going on there with the shaking but I can tell you it has to do with your transmission. Hopefully it was just a hick-up. Let us know.

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