2008 ford expedition knock sensor replacement time?

2008 ford expedition has a bad knock sensor about how long should it take to replace it. I know what it all entails I just don't know how much time to set aside.

Book time is around 4 hours… Have to remove the intake manifold to get at the sensors…2 of them… Might be best to replace both since they are so hard to get at and 1 might fail later if only 1 is bad now. Make sure to mark all wiring connections carefully and torque all the bolts properly.

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http://www.f150online.com/forums/2004-2008-f-150/476635-850-knock-sensor-replacement.html