GM Full Size Vans 1987-1997 Repair Guide

PCV Valve

Print

See Figures 1 and 2

Diesel engines do not utilize a PCV system.

The PCV valve, which is the heart of the positive crankcase ventilation system, should be changed as noted in the Maintenance Intervals chart at the end of this section. The main thing to keep in mind is that the valve should be free of dirt and residue and should be in working order. As long as the valve is not showing signs of becoming damaged or gummed up, it should perform its function properly. When the valve becomes sticky and will not operate freely, it should be replaced.



Click image to see an enlarged view

Fig. Fig. 1: PCV valve location - 4.3L, 5.0L and 5.7L engines



Click image to see an enlarged view

Fig. Fig. 2: PCV valve location - 7.4L engine

The PCV valve is used to control the rate at which crankcase vapors are returned to the intake manifold. The action of the valve plunger is controlled by intake manifold vacuum and the spring. During deceleration and idle, when manifold vacuum is high, it overcomes the tension of the valve spring and the plunger bottoms in the manifold end of the valve housing. Because of the valve construction, it reduces, but does not stop, the passage of vapors to the intake manifold. When the engine is lightly accelerated or operated at constant speed, spring tension matches intake manifold vacuum pull and the plunger takes a mid-position in the valve body, allowing more vapors to flow into the manifold.

The valve is either mounted on the valve cover or in the line