Thread: 2001-F150 5.4 Eng. bucking/stumble help!!!
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Old 03-20-2008, 04:47 PM
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KingRanchMan02
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As spark plugs wear, the spark plug gap increases which makes the voltage required to fire them to go up. The gap eventually gets wide enough to cause the coil to be stressed when engine loads are very high. The stressed coil will get overheated and turns of the coil will short out, which limits the voltage output of the coil.

With the voltage output of the coil down and the engine load high, the bucking comes in. The misfire is not repetative enough to set a code in the computer. The only way to identify the problem is for the dealer to do a COP stress test to find the one that is bad.

My truck by the way has started this same thing. I am on my original plugs with 78k miles. Good luck!
 
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