1998 Ford F150 Roush V8 - Where is the Power Control Module and what does it do?

 

The PCM is basically the brain of the truck that tells everything what to do when to fire gas air ration etc. mine is under the passenger side under kick panel.

 

The PCM controls/ manages fuel, timing, and spark based on sensor inputs. It also establishes memory of the operation of the engine like Long Term Fuel Trims. It also trips 'check engine light' based on the sensor info it receives.