How to Know if the Belt Tensioner Is Bad in a 2002 4.2 F-150

Ford offered the 2002 F-150 1/2-ton pickup with a 4.2-liter V-6, 4.6-liter V-8 or a 5.4-liter V-8. The 4.2-liter, like the larger V-8 engines, uses a serpentine drive belt system for conveying engine torque to the engine accessories to power them. The serpentine belt winds its way around the accessory pulleys, turning them as it turns across the crankshaft pulley. A spring-loaded automatic belt tensioner holds the serpentine belt taut on the pulleys. Once the spring in the tensioner begins to weaken, the tensioner goes bad before ultimately failing.

Instructions

1

Turn off the F-150's 4.2-liter engine. Open the truck's hood.

2

Examine the serpentine belt routing sticker, located on the fan shroud, to pinpoint the location of the automatic belt tensioner on your F-150. The tensioner is just right of center on the front engine cover, but its location in relation to the other components will vary based on engine accessory configuration.

3

Shine the flashlight on the automatic belt tensioner hub to illuminate the belt tension range markings. If the indicator mark is in between the maximum and minimum tension marks, the automatic belt tensioner is in good working order. If the indicator mark is on the side of the minimum mark furthest from the maximum tension mark you may have a bad tensioner.

4

Shine the flashlight on the serpentine belt. Examine the serpentine belt at several locations along its length for signs of age such as frayed edges, cracked ribs or rib loss. If the belt has none of these signs, the tensioner is bad.

5

Start the 4.2-liter engine. Watch the automatic belt tensioner arm as the serpentine belt travels along the tensioner pulley. A bad tensioner will have an arm that jitters and vibrates noticeably as the belt turns.