Q: I have a 2005 Lincoln navigator that the number 6 spark plug is misfiring on.

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My car sp[uters when accelerating over 40 mph, after a min or so it feels like it clears out and you regain your power. I took it in to firestone and they told me my number 6 spark plug was misfiring causing it to sputter. They then told me it would cost 675 to correct?

My car has 119000 miles.
My car has an automatic transmission.

Hello. A misfire can be caused by a number of things. Depending on what they found to be the problem it is quite possible that this is an accurate estimate. Most of the time this is caused by a failure in the ignition coil, but it may need spark plugs also. In a lot of cases this can also be caused by a valve seat failure in the engine but that will typically cost much more to fix. From my experience with this vehicle I would suspect an ignition coil which should not cost this much. I would get a second opinion, like from YourMechanic, where a certified mechanic can come to you do [diagnose why the engine is misfiring] https://www.yourmechanic.com/services/engine-is-misfiring-inspection

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