The 4.6L DOHC engine uses hydraulic valve lash adjusters that do not require any adjustment.
The 3.8L and 5.0L engines are equipped with hydraulic lifters. The lifters are located in bores in the cylinder block. As the camshaft turns, a camshaft lobe forces the lifter upward in its bore. The lifter drives a pushrod upwards and acts on a pivoting rocker arm, which in turn opens the valve. When the valve opening event is over and the base circle of the camshaft lobe contacts the hydraulic lifter, the valve spring pulls the valve closed. The function of the hydraulic valve lifter is to maintain zero valve lash during the entire valve opening and closing process; any lash is instantaneously taken up by hydraulic action.
The hydraulic lash adjuster/lifter consists of 3 main parts: the body, the plunger and the valve. Oil under pressure from the engine lubricating system passes through the check valve and forces the plunger upward in the body of the lash adjuster/lifter. The plunger contacts the roller follower in the case of the lash adjuster or the pushrod in the case of the lifter. The oil pressure removes all clearance between the 2 parts. The valve spring prevents the valve from being lifted of its seat.
During the valve opening event, the pressure from the valve spring forces the ball check valve onto its seat, preventing most of the oil from escaping from the lash adjuster/lifter. The lash adjuster/lifter now acts as a solid link. Some oil is designed to escape from the lash adjuster/lifter to prevent the possibility of negative clearance, which would keep the valve open slightly.
When the valve is closing, any oil lost from the lash adjuster/lifter is replaced by the engine lubricating system. Again, the oil pressure forces the plunger upward to contact the follower or pushrod. The plunger constantly moves up and down a small amount within the bore of the lash adjuster/lifter, in this manner. On impact with the rocker arm or pushrod, it moves downwards and, when relieved of the valve spring pressure, oil pressure forces it upwards.
The components of the hydraulic valve lash adjusters and valve lifters are manufactured to very close tolerances, so regular engine oil and filter changes are necessary. Any dirt that gets into the lash adjuster/lifter can cause the check valve to malfunction and the plunger to wear, causing poor engine performance and noisy valve train operation.
The lifters used in the available family of engines are hydraulic and do not require any adjustment as part of a maintenance program. However, if a mechanical condition occurs where the valve train was disturbed, then use the following procedures to maintain proper valve lash.
Adjustment of the hydraulic lash adjusters or hydraulic lifters is neither possible nor necessary.